Teacher guide grade 8

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SScciieennccee
Teacher’s Guide
Department of Education
Republic of the Philippines
8
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Science – Grade 8
Teacher’s Guide
First Edition, 2013
ISBN:
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Published by the Department of Education
Secretary: Br. Armin A. Luistro FSC
Undersecretary: Yolanda S. Quijano, Ph.D.
Department of Education-Instructional Materials Council Secretariat (DepEd-IMCS)
Office Address: 2nd Floor Dorm G, Philsports Complex
Meralco Avenue, Pasig City
Philippines 1600
Telefax: (02) 634-1054 or 634-1072
E-mail Address: imcsetd@yahoo.com
Development Team of the Teacher’s Guide
Authors: Pia C. Campo, May R. Chavez, Maria Helen D.H. Catalan, Ph.D.,
Leticia V. Catris, Ph.D., Marlene B. Ferido, Ph.D., Ian Kendrich C. Fontanilla,
Ph.D., Jacqueline Rose M. Gutierrez, Shirley R. Jusayan, Michael Anthony B.
Mantala, Cerilina M. Maramag, Marie Paz E. Morales, Ph.D., Eligio C. Obille,
Jr., Digna Paningbatan, Genevieve Faye Pasamonte, Ma. Dulcelina O.
Sebastian, Rolando M. Tan, and Rodolfo S. Treyes, Ph.D.
Reviewers: Ernelea P. Cao, Ph.D., Josefina Ll. Pabellon, Ph.D., Ma. Cristina
D. Padolina, Ph.D., Risa L. Reyes, Ph.D., and Merle C. Tan, Ph.D.
Illustrators: Alvin J. Encarnacion, Ma. Laura V. Ginoy, Rizaldo Ramoncito S.
Saliva, and Andrew F. Torres
Layout Artist: Cecile N. Sales

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Page
Module 1. Forces and Motion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Balanced and Unbalanced Forces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Activity 1: Forces on objects at rest . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Activity 2: Balance of forces. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Newton’s Three Laws of Motion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Newton’s First of Motion: Law of Inertia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Activity 3: Investigating inertia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Newton’s Second Law of Motion: Law of Acceleration . . . . . . . . . . . . . . . . . . 12
Activity 4: Force and acceleration . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Newton’s Third Law of Motion: Law of Action-Reaction . . . . . . . . . . . . . . . . . 15
Activity 5: Action-reaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Module 2. Work and Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
What is Work?. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Activity 1: Is there work done? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Calculating Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Work is a Method of Transferring Energy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Kinetic Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Potential Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Activity 2: Rolling toy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Work, Energy, and Power. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Activity 3: How POWER-ful am I? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Module 3. Heat and Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Activity 1: Explaining hotness or coldness . . . . . . . . . . . . . . . . . . . . . 29
Activity 2: Dye in water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Thermal Expansion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Phase Change . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Activity 3.1: What happens when ice melts? . . . . . . . . . . . . . . . . . . . . 33
Activity 3.2: What happens to the temperature of water as it boils?. 35
Activity 4: What is the relationship between the mass of a material
and the amount of heat it can transfer?. . . . . . . . . . . . . . . 35
Activity 5: Comparing heat capacities . . . . . . . . . . . . . . . . . . . . . . . . . 36
Module 4. Electricity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Current and Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Activity 1: Current and voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Current and Resistance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Activity 2: Current and resistance . . . . . . . . . . .. . . . . . . . . . . . . . . . . . 42
Electrical Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

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Activity 3: What’s the connection? . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
Safety in Using Electricity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
Activity 4: Stay safe! . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
Module 5. Sounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
Activity 1: The dancing salt and the moving beads!. . . . . . . . . . . . . . . 52
Activity 2: Characteristics of waves: Comparing longitudinal and
and transverse waves . . . . . . . . .. . . . . . . . . . . . . . . . . . 53
Activity 3: Sound race… Where does sound travel fastest? . . . . . . . . 53
Activity 4: Chimes… Chimes… Chimes… . . . . . . . . . . . . . . . . . . . . . . . . 54
Activity 5: Faster sound… In hotter or cooler? . . . . . . . . . . . . . . . . . . . 55
Activity 6: Reflecting and refracting sound. . . . . . . . . . . . . . . . . . . . . . 55
Module 6. Colors of Light . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
Activity 1: The colors of the rainbow… The colors of light. . . . . . . . . . 60
Activity 2: Red versus violet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
Activity 3: Which color has the MOST energy? . . . . . . . . . . . . . . . . . . 61
Activity 4: The color spectrum wheel revisited . . . . . . . . . . . . . . . . . . 62

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UNIT 1
Force, Motion, and Energy

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UNIT 1: Force, Motion, and Energy
In Grade 7, students learned about the various forms of energy, namely
motion energy, light, sound, heat, and electrical energy. They learned about the
different energy forms in terms of their sources, their nature or characteristics, and
the ways by which they can be transferred from one object or place to another. In
Grade 8, students deepen their understanding of energy by describing how energy
transfer affects, and is affected by, matter. They explore some changes when there
is energy transfer such as changes in temperature, changes in the current in a
circuit, or changes in the speed of sound travelling through a medium. They relate
these changes to the energy of the particles that make up matter.
This unit has six modules. The first two modules deal with the transfer of
energy by applying force to large objects; Modules 3 and 4 discuss changes in
energy of the particles of matter which accompany energy transfer; and Modules 5
and 6 describe the interaction between waves and matter. Most of the lessons found
in each module take off from the lessons covered in Grade 7.
The table below shows the general and specific topics covered in Grade 8:
Module Title Specific Topics Focus Questions
Forces and
Motion
Balanced and Unbalanced Forces
Laws of Motion
How do forces affect the motion of an
object?
Work and
Energy
Work
Kinetic and potential energy
How are work and energy related?
Heat
Effects of heat on matter
Factors affecting the amount of heat
transferred
How does heat affect matter?
Electricity
Voltage-current- resistance
relationship
Series and parallel circuits
What are the factors that affect the
current in a circuit?
Sound
Speed of sound
Reflection and refraction of sound
What are the factors that affect the
speed of sound?
Light
Color, wavelength, frequency, and
energy of light
What properties of light explain the
separation of colors in white light?

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Most of the topics in this module are dealt with qualitatively in order for
students to have a basic understanding of the concepts. Some tasks include
measurements and computations to illustrate the relationship among quantities. The
activities included in each module aim to make students interested in these topics
and motivate them to learn more in the succeeding grade levels.

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FORCES AND MOTION
In Grade 7, students learned the different ways of describing the motion of an
object in one dimension. This time, they will learn to explain the motion of an object
using Newton’s laws of motion. They will describe the relationship between the
forces acting on an object and its motion due to these forces.
Key questions for this module
Do forces always result in motion?
What are the conditions for an object to stay at rest, to keep moving at
constant velocity, or to move with increasing velocity?
How is force related to acceleration?
Unit 1
MODULE
1
1. If an object stays at rest, there is no force acting upon it.
2. An object continues to move at constant velocity because a
constant force acts on it.
3. If the speed of an object increases, its acceleration also increases.
4. Objects move because they have a force; they stop when their
force is already used up.
Related Misconceptions

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Balanced and Unbalanced Forces
To introduce the concept of FORCE, place an object on top of a table and
ask:
Is this object at rest or in motion? What evidence can you give to support
your answer?
Then continue the discussion by asking the following questions:
Will this object move by itself? When will it move? Or how can we make it
move?
(While the object is moving) How can we make it move faster? Move slower?
Change its direction? Stop?
Some students can be asked to demonstrate some ways to make the object
move or change its state of motion. Then ask:
What ‘common thing’ did you do on the object to make it move, stop, or
change its speed?”
This will lead them to realize that the object can be made to move, stop, or
change its speed or direction by pushing or pulling. The motion of the object can be
changed if FORCE is applied on it. Then place again the object on top of the table
and ask:
Since this object is now at rest, can we then say that there is/are no force/s
acting on it?
Then let them do Activity 1.

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In this activity, students are asked to identify the forces acting on objects at
rest.
Teaching Tips
1. Students may be asked to work on the activity in pairs or in smaller groups to
ensure that they will all be actively involved while doing the activity.
2. During the post activity discussion, students can be asked to recall what they
learned in the previous grades about the force (pull) of gravity. They may be
asked to show or cite examples that demonstrate the presence of gravitational
pull on Earth. If there is enough time, discuss more about gravitational force.
Emphasis should be given on the following ideas:
 Gravitational force is the attraction between any two objects or bodies with
mass. If the mass of either object increases, the gravitational force between
them also increases.
 As the Earth attracts objects around it, these objects also attract the Earth.
But the Earth is much more massive than them that is why their attraction is
not as great as the gravitational pull of the Earth.
 All things on Earth fall (or are attracted) towards the center of the Earth.
3. During the discussion, emphasize that when objects are at rest, it does not mean
that there are no forces acting on them (Misconception #1). Then ask the
students this question:
Then what makes them stay at rest (even if there are forces acting on them)?
Then let them perform Activity 2.
Forces on objects at rest
Activity
1

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Answers to Questions
Situation 1: Hanging pen
Q1. The pen is at rest.
Q2. Yes. The forces acting on the pen are the
force exerted by the string on the pen and the
force of gravity.
Q3. When we cut the string, the pen fell to the
ground because gravity pulled on it downward.
Situation 2: Book on a table
Q4. The book is at rest.
Q5. Yes. The forces acting on the book are
the force exerted by the table on the
book and the force of gravity.
Q6. No, the book stays at rest. The book can
be moved by pushing it on one side
only.
The aim of this activity is to help the students understand and explain how the
forces acting on the objects in Activity 1 help in keeping them at rest.
Teaching Tips
1. Each group can work first on the activity using a pair of spring balances. Then
they can join another group to complete the 4 spring balances needed for the
challenge part (Step 7).
2. During the post activity discussion, emphasis must be given on the following
ideas:
Balance of forces
Activity
2
Hanging pen
Tension
force
Force of
gravity
Book on a table
Normal force / Force
exerted by the table
on the book
Force of
gravity

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 If two forces acting on an object are equal in magnitude but opposite in
direction, they are considered as balanced forces. These forces must lie
along the same line.
 If the forces acting on an object are balanced, the object either stays at rest
or continues to move at constant velocity.
 If the forces acting on an object are unbalanced, the state of motion of the
object will change. (This concept was discussed in the module using the
rolling ball as an example). Emphasize that the ball slowed down and
eventually stopped not because its force is already used up (misconception).
The ball slowed down and stopped because an unbalanced force (friction)
caused it to change its motion.
Q7. The forces are equal in magnitude but opposite in direction.
Q8. If the lines of action of the forces are extended, they meet at a single point.
Note: At this point, the term “concurrent forces” may be introduced. When the lines
of action of the forces acting on an object meet at a single point, they are
considered as concurrent forces. When the forces acting on an object are
concurrent, the object does not move nor rotate.
Concept check:
1. A boy and a girl pull a heavy crate at the same time with 10 units of force each as
shown in the diagram. What is the net force acting on the object?
2. What if the boy and the girl pull the heavy crate at the same time in opposite
directions with 10 units and 5 units of force respectively, what will be the net
force acting on the object? Will the object move? To what direction will it move?
10 units5 units
10 units
10 units

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3. Suppose another girl pulls the heavy crate with 5 units of force in the same
direction as the girl, what will be the net force acting on the object? Will the object
move?
Answers:
1. Fnet = 20 units
2. Fnet = 5 units. The object will move in the direction of the 10-unit force.
3. Fnet = 0. The object will not move.
Newton’s Three Laws of Motion
1. Start the session by introducing first Isaac Newton to the students. Provide
some pictures if possible. Discuss some of his significant contributions
especially in the field of physics, e.g., Newton combined his ideas and the
ideas of the other scientists like Galileo to give us a more unified picture of
how our universe works. He formulated the laws of motion and gravitation.
Through his three laws of motion, we can describe and predict the movement
of everything around us.
Newton’s First Law of Motion: Law of Inertia
This activity demonstrates how the inertia of an object affects its motion.
Inertia is the tendency of the body to resist changes in its state of motion. This is
described through Newton’s First Law of Motion, also referred to as Law of Inertia.
Investigating inertia
Activity
3
10 units5 units
5 units

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Teaching Tips
1. After discussing the result of the activity, relate the Law of Inertia to the previous
discussion on balanced and unbalanced forces. Emphasize that if an object is
acted upon by balanced forces, its motion or its velocity will not change. Since
acceleration is defined as the change in velocity over time, then we can say that
the object will not accelerate. It will only accelerate if the forces acting on it are
unbalanced. This is what the Law of Inertia is all about. It states that, “An object
will stay at rest or move at constant velocity unless an unbalanced external force
acts on it.”
2. If time permits, discuss also the effect of mass on inertia.
3. For the application part, relate the concept of inertia to the students’ experience
while riding a vehicle. Then discuss the importance of using a seatbelt.
Coin Drop
Q9. When we slowly pulled the cardboard, the coin on top moved with the
cardboard.
The frictional force between the coin and the cardboard had caused the coin
to stay on top of the cardboard and move with it.
Q10. When we flicked the cardboard with our finger, the cardboard moved forward
but this time, the coin did not move with it. So when the cardboard was
removed from underneath the coin, the coin dropped into the glass.
The coin did not move forward with the coin because of its inertia.
Stack of Coins
Q11. When we hit the bottom coin with the edge of the ruler, the coin moved out
from the pile but the other coins stayed in place. The inertia of the other coins
has caused them to stay in place or not to move out with the coin that was hit
by the ruler.

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Newton’s Second Law of Motion: Law of Acceleration
 To introduce the second law of motion, refer the students back to the
discussion on the effects of unbalanced forces on the motion of objects by
saying:
If the forces acting on an object are unbalanced (Fnet˃0), the object
accelerates. But how is the acceleration of the object related to the amount
of the net force acting on it?
In this activity, students will analyze and describe the relationship between
the unbalanced external force acting on an object and its acceleration using tape
charts.
Note that the students will not actually perform the activity using the ticker
tape timer. It will be assumed that some other students have done it already. What
they will just do is to analyze the tape charts that are supposedly obtained by the
students who performed the activity.
Teaching Tips
1. Reproduce the tape charts found in the teacher’s guide (Figure 3) to be
distributed among the students.
2. If the materials are available, try to demonstrate how the data or tape charts were
obtained. To do this, hang four identical rubber bands from one end of a wooden
bar as shown in Figure 1. Then mark on the wooden bar the position where the
rubber bands should be stretched (Figure 2). When the rubber band is stretched,
it pulls with it the cart. Make sure that the person holding the wooden bar with
rubber bands is free to move and ready to run with the dynamics cart, if needed,
to maintain the length by which the rubber band is stretched while pulling the
cart. This is to ensure that the force acting on the cart is constant. The number of
rubber bands used to pull the cart is related to the amount of force acting on the
cart. If the number of rubber bands is changed, say doubled, the force acting on
the cart is considered also to be doubled.
Force and acceleration
Activity
4

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3. In the absence of a ticker tape timer, students can be allowed to watch a video
showing what a ticker tape timer is and how it works to produce tapes with dots.
4. Note that the ticker timer in the activity produces 60 dots on the tape per second.
This is why the time interval (equivalent to 6 dots) = 0.10 seconds. (Just like 30
dots = 0.5 seconds; 15 dots = 0.25 seconds, and so on.)
5. Students may work on the activity as a group. But if there are enough copies for
everyone, they can be asked to work on Part A first individually. Then, assign
each group with a specific tape chart to work on.
6. Note that their measurements may differ even if they are provided with the same
copies of the tape charts. Make sure to discuss the reasons for the differences in
their measurements.
7. Ask the students to compute for the acceleration three times using different
values of ∆v (from Step 6). Then ask them to get the average value.
8. Ask the students to obtain the other values of acceleration (average only) from
the other students who worked on the other tape charts to complete the data for
F = 1 unit to F = 4 units. Then ask them to use the data to come up with a
relationship between the net force acting on the body and its acceleration.
9. Use the result of the activity to discuss about Newton’s second law of motion, or
Law of Acceleration. If there is still enough time, students can also be asked to
plot the graph of force against acceleration (Figure 4 below). This is also another
way of showing the relationship between the two variables.
10. Since the law of acceleration quantifies the relationship among mass, force,
and acceleration, it is better if the relationship between the mass of the object
and its acceleration will also be discussed.
Figure 1
Figure 2

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As the mass of the object increases, with the same amount of force applied, its
acceleration also increases. To state in another way, if the same force acts on
two bodies of different masses, the acceleration of the body with lesser mass is
greater than the acceleration of the body with greater mass.
Tape chart analysis
Q12. (Similarities) The lengths of the strips are increasing.
(Differences) The change in length differs among the tape charts.
Q13. The change (increase) in the length of the strips means that the average
velocity of the cart increases at equal time interval.
The cart is accelerating.
This is also true to all other tape charts.
Q14. The increase in length of the strips in F = 1 unit is almost the same or
constant.
This indicates that the velocity of the cart increases uniformly at equal
intervals of time when the force acting on it is constant.
Q15. The amount of change in the length of the strips varies among the tape
charts. It is greatest in F = 4 units and least in F = 1 unit.
Q16. When the dots on top of the strips are connected, a straight line was formed.
Yes, the same pattern exists for the other tape charts.
Quantitative analysis
Q17. The computed values of vave are increasing. This indicates that the cart is
accelerating.
Q18. The computed values of ∆v are equal (or almost equal).
This means that the cart is accelerating uniformly or its acceleration is
constant.
Q19. The computed values of acceleration are equal (or almost equal).

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Q20. The acceleration of the cart increases with the net or unbalanced force
applied on it. Or as the amount of force applied on the cart increases, the
acceleration of the cart also increases.
Newton’s Third Law of Motion: Law of Action - Reaction
The Newton's third law of motion, or sometimes called as Law of Action-
Reaction, describes the relationship between the forces that two bodies exert on
each other. In this activity, students should realize that these forces are equal in
magnitude but opposite in direction.
Q21. (Answer may differ, but the values should be equal)
These values represent the amount of pulling force that we exerted on each
other.
Q22. The forces that we exerted are in opposite directions.
Q23. (The readings this time should be greater than the previous ones)
Q24. We increased the force that we exerted on each other.
Q25. (readings may vary)
Q26. The forces are of opposite directions.
Action-reaction
Activity
5

16
Figure 3: Tape charts
F= 2 unitsF=1 unit F= 3 units F= 4 units

17
Sample computation for F= 2 units
Strip
Number
Length of
strip
(cm)
Average velocity, vave
(cm/s)
Change in
velocity, v
Acceleration
(cm/s2
)
1 1.1 11 11 110
2 2.2 22
10 100
3 3.2 32
11 110
4 4.3 43
12 120
5 5.5 55
aave = 110 cm/s2
Sample data for Table 1
Force # of rubber bands Acceleration
F = 1 unit 1 55 cm/s2
F = 2 units 2 110 cm/s2
F = 3 units 3 165 cm/s2
F = 4 units 4 221 cm/s2

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References and Links
Herr, N. (2008). The sourcebook for teaching science: Strategies, activities, and
instructional resources, grades 6-12. San Francisco, CA: Jossey-Bass.
Department of Education, Culture and Sports. (DECS). (n.d.). Physics teachers
resource manual. Pasig City. Author.
Department of Education. (DepEd). (2002). Lesson Plans for the 2002 Basic
Education Curriculum: Science IV. Pasig City. Author.
The Physics Classroom (1996-2013). Newton’s laws. Retrieved from
www.physicsclassroom.com
University of the Philippines National Institute for Science and Mathematics
Education Development. (2002). Practical work on high school physics:
Sourcebook for teachers. Quezon City: Author.
Figure 4: Graph of force vs acceleration
Acceleration
(cm/s2
)
1 2 3 4
50
100
0
150
0
200
0
Force (unit)
250
0

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WORK AND ENERGY
In this module, students will learn about motion from the perspective of work
and energy. The concept of energy is one of the most important concepts in physics.
The students have been studying about it since Grade 3 up to Grade 7. They have
learned that energy takes many forms; there are different sources and uses of
energy; and energy can be transferred.
The module starts with a discussion about work. In the first activity, they will
explain whether a situation represents an example of work. It is followed by a
discussion about work and energy, and then about kinetic and potential energy. In
the second activity, students will construct a toy that demonstrates how a rubber
band ‘stores’ energy. The last activity puts together the concepts of work, energy and
power.
What is Work?
Figures 1 to 3 in the student’s module shows different situations. Ask the
students to identify the one doing the work and on which object the work is done.
The students should be able to arrive at the concept that work is done on an
object when the force applied to it covers a distance in the direction of the applied
force.
What is work?
What is energy?
How are work, energy and power related?
Unit 1
MODULE
2

20
In this activity, students will analyze the situations shown in the illustrations.
For them to explain if the situations represent examples of work they should be able
to identify the one doing the work and on which object the work is done. They should
also look into the direction of force exerted relative to the direction of the movement
of the object or the distance covered by the applied force.
Teaching Tips
1. Ask the students what’s the first thing that comes to their mind when they hear
the word work.
2. Let them look for the meaning of work in a dictionary.
3. Recall the lesson about force in Module 1.
 A girl is pulling her toy car.
Yes, the situation is an example of work. The work is done by the girl on the
cart. The force exerted by the girl in pulling the toy car is in the same direction
as the distance covered when the force is applied.
 A man is lifting a box to be placed on a table.
Yes, the situation is an example of work. The work is done by the man on the
box. The force exerted by the man is upward and the box is displaced
upward.
 A girl carrying a bag walks down the street.
No, the situation is not an example of work. There is force (the shoulder
pushes up the bag) and there is displacement (the bag is moved
horizontally). However, the line of action of the force and the displacement
are not parallel but perpendicular. The distance covered is not along the
direction of the applied force.
Is there work done?
Activity
1

21
 A mango fruit falling from the branch
Yes, the situation is an example of work. The work is done by the force of
gravity on the mango. In this case, the mango loses energy as you will find
out in the discussion of potential energy.
Calculating work
The students are given the equation of work in their module. However, the
equation can only be used if the force is applied horizontally (pushed across the floor
or ground) or vertically (lifted above).
Figure 1. Equation for solving work
The equation of work for forces at an angle is not introduced to the students
because they have not yet taken up trigonometric functions in their mathematics
class. However, if the students ask how to solve for work if the force is at an angle,
you may also show the equation.
Figure 2. Equation for solving work if the force is at an angle
d
force
d
force
force

22
Answer to the problem
A book which has a mass of 1 kg is on the floor. If the book is lifted from the
floor to the top shelf which is 2 meters from the floor, how much work is done?
Work is a Method of Transferring Energy
 In Grade 7, students learned that there are different ways by which energy can
be transferred from one place to another. This time, they will learn that work is a
means of transferring energy from one object to another.
 Is there work done on the ball? In the bowling game described in the student’s
material, the work is done by the person on the ball to just start it moving.
Because of the work done to the ball, it gained ‘something’ that enables it to
move. That ‘something’ that was transferred to the ball is called energy. The
energy became energy of motion of the ball.
 What can a moving ball do? A moving ball has energy. When it strikes the empty
plastic bottle, it can push it through a distance. Thus, work is done by the ball on
the empty plastic bottle. Since work is done on the bottle, energy is transferred to
it.
 If energy can be transferred, what happens to the energy of the one doing the
work and to the object on which work is done? The one doing the work loses
energy and the object on which work is done gains energy. When work is done
by an object, the object loses energy; when work is done on an object, the object
gains energy. In the bowling game the students played, the one rolling the ball
loses energy while the ball gains energy. When the moving ball strikes the empty
plastic bottle it loses energy while the plastic bottle gains energy.

23
 Clarify to the students that it is energy and not force that is transferred when work
is done.
 You may also show or demonstrate a billiard game wherein one ball hits another
ball.
Kinetic Energy
 The energy of a moving object is called energy of motion or kinetic energy (KE).
How the equation of KE is derived is shown in the student’s module.
 The KE of an object depends on its mass and velocity. What will happen to the
KE of an object if its mass is doubled but the velocity remains the same? The KE
will be doubled. How about if the velocity is doubled but the mass remains the
same? The KE is proportional to the square of the speed, thus if the speed is
doubled, the KE will be quadrupled.
Answer to the problem:
A 1000 kg car has a velocity of 17 m/s. What is the car’s kinetic energy?
Potential Energy
Work is done in lifting an object. When work is done on an object, energy is
transferred to it. Thus, an object lifted from the ground gains energy. Since the work
is done against the force of gravity, it is called gravitational potential energy or simply
potential energy (PE).
The force of gravity also acts on objects falling to the ground. As an object
falls, the potential energy decreases because it is transformed to become the kinetic
energy of the object.

24
The gravitational potential energy is the energy due to its position. This
energy depends on the mass and height of the object. The height can be measured
relative to an assigned level. But usually, the common reference level is the ground.
Teaching Tips
1. Point out that the higher the object is from the ground, the greater is its potential
energy. The more massive an object is, the greater is its potential energy. These
concepts were demonstrated in the problems.
2. Compare the potential energy of an object/s for different reference level.
Answer to the problem:
If the same 1.0 kg book is lifted 0.5 m above the table, but the table top is 1.0 m
above the floor, what would be the potential energy of the book if the reference level
were the floor?
 Prepare a sample toy made of a can instead of the transparent plastic
container. This way the students cannot see the mechanism inside the can.
Rotate the barbecue stick beforehand before asking them what they think will
happen to the can when placed on the floor.
Rolling toy
Activity
2

25
 After the activity, ask the students to demonstrate the game they played
using a rubber band. Ask them how the rubber bands ‘store’ energy and what
this energy can do once transformed to kinetic energy.
Q1. It rolls.
Q2. Potential energy
Q3. Kinetic energy
Q4. Potential to kinetic energy
Work, Energy and Power
People possess energy. They get their energy from the food they eat. As
shown and demonstrated in the previous lesson, this energy can be transferred to
objects.
When people do things such as walking or running, they expend energy. The
rate at which they expend energy is called power. Power is the rate of doing work or
the rate of using energy.
In this activity, the students will relate the concepts of work and energy to
power. The energy expended in climbing a flight of stairs is equal to the gravitational
potential energy, PE = mgh or weight x height.
How POWER-ful am I?
Activity
3

26
Name
Weight
(N)
Height of
stairs (m)
Time taken to
climb the stairs
(s)
Energy
expended
(J)
Power
(J/s)
Bella 441 5 10 2205 220
Troy 490 5 8 2450 306
Mae 392 5 10 1960 196
Elijah 441 5 9 2205 245
Answers to Questions (based on the sample data for Table 1)
Q5. Troy
Q6.
Q7. Mae
Q8.
Q9. Each member performed different amounts of work except for Bella and
Elijah who performed the same amount of work because they weigh the
same.
Q10. Power output is determined by the amount of work done or energy expended
and the time taken to do the work.
Summary
Below is a list of concepts or ideas developed in this module.
 Work is done on an object when the force applied to it covers a distance
in the direction of the applied force.
 Work is a way of transferring energy.
 When work is done by an object it loses energy and when work is done
on an object it gains energy.
 The energy of an object enables it to do work.

27
 A moving object has energy called energy of motion or kinetic energy.
 An object above a specified level has energy due to its position called
potential energy.
 An elastic object that is stretched or compressed or twisted has energy
called potential energy.
 Power is the rate of doing work or the rate of using energy.
Henderson, Tom. (2013). Work and energy. Retrieved from
https://itunes.apple.com/us/book/work-and-energy/id611940649?mt=13
Hewitt, P.G. (2002). Conceptual physics. USA: Prentice-Hall, Inc. Saddle River, New
Jersey.
Kirkpatrick, L.D., & Wheeler, G.F. (1998). Physics: A world view. Forth Worth:
Saunders College.
Ostdiek, V.J., & Bord, D.J. (1987). Inquiry into physics. New York: West Publishing.
DepEd. Science and Technology IV. SEDP Series. (1992). Philippines: Book Media
Press, Inc.

28
HEAT AND TEMPERATURE
In Grade 7, students learned about the conditions necessary for heat transfer
to occur and the ways by which heat transfers from one place to another. This time,
they will explore what happens to an object when heat is transferred to or from it.
They will also explore the factors that affect the amount of heat that an object can
transfer.
What happens to solids, liquids, or gases when they absorb or
release heat?
Does heat affect all kinds of materials in the same way?
Are heat and temperature one and the same?
Unit 1
MODULE
3
1. Heat is a substance.
2. Heat is not energy.
3. Heat and temperature are one and the same.
4. The temperature of an object depends on its size or volume.
5. The amount of heat transferred is determined always by the change
in temperature.

29
Notes:
 This module is good for 6 days. The experiments were made simple so that
students will be able to finish them early and the discussion of the results can
be done also on the same day.
 The word heat in the module is written in italic form to emphasize that it
represents the quantity of thermal energy that is transferred to or from an
object.
 Since the students will be using laboratory thermometers in most of the
experiments that they will do, it is recommended that the guides on how to
handle properly the thermometer and use it to measure temperature are
discussed clearly at the beginning of the chapter.
In this activity, students will describe the hotness or coldness of water in
terms of its temperature. They will also compare the amount of heat transferred to
the water in terms of the changes in its temperature and come up with a relationship
between these two variables.
Teaching Tips
1. The first part of the activity requires the students to recall their previous lesson on
heat transfer. Since this is just a review, students may be allowed to discuss their
answers within their group. Make sure that the following concepts are clear to the
students:
 Heat is a transfer of (thermal) energy between objects or places due to
temperature difference.
 Heat transfers from an object of higher temperature to an object of lower
temperature.
2. When students are asked to determine the hotness of the water through
sensation, make sure that they use a different finger for each water sample. The
explanation can be found in Grade 7 (Module 5: Heat Transfer).
Explaining hotness or coldness
Activity
1

30
3. Note that heat transfer may continuously take place between the cold water and
the surrounding (as long as there is a temperature difference). So there will be a
possibility that the values of the initial temperature of the water inside the three
containers will vary even if the cold water was taken from the same source.
(Refer to the table below.) Make sure to discuss about this during the post
activity discussion.
Sample Data
Container
Temperature Change in
TemperatureInitial Final
Container 1 12°C 56°C 44C°
Q1. Heat was transferred from my finger (lower temperature) to the water (higher
temperature).
Q2. Cold. The energy was released from my hand to the water.
Q3. (Answers may vary)
Q4. Container 1. The container that was added with hot water.
Container 3. The container that was added with cold water.
Q5. Because of the different temperatures of the water added to the containers.
Q6. Heat transfer took place in containers 1 and 2. There were changes in the
temperature of water inside these containers.
Q7. Greater amount of heat was transferred in container 1. There was greater
change in the temperature of water.
Q8. The amount of heat transferred is proportional to the change in temperature.
The greater the amount of heat transferred to an object, the greater the
increase in its temperature.

31
The aim of this activity is to explain why the temperature of water in Activity 1
increases when heat was added to it. Also, by observing the behavior of the dye
through the water, students will be able to describe the changes that occur due to
heat transfer at the particle level.
Teaching Tips
1. At this point, students should be made to realize that everything is made up of
moving particles.
2. In Table 2, last column, students’ observations must focus on the scattering of
the dye through the water. Ask them to make comparisons, like the dye scatters
faster (or slower) or the dye scatters the most (or the least). They will later relate
these observations to the speed of the moving particles.
3. At the end of the discussion, students should be able to recognize that “hotness
or coldness” indicates how fast the particles move. “Hot” may be considered as
faster movement of the particles or higher kinetic energy of the particles.
4. During the post activity discussion, emphasis must be given on this idea
 The change in the kinetic energy of the particles of a substance varies with
the amount of heat transferred to it. The greater the amount of heat
transferred, the greater the increase in the kinetic energy of the particles. In
the case of the dye, the particles of the dye added to the container with hot
water move faster due to the greater amount of energy transferred to them
from the hot water. This makes the dye scatter faster throughout the medium
(water).
Dye in water
Activity
2

32
Container
Temperature
(0
C)
Observations
Container 1 (cold) 12 0
C Dye scattered the slowest
Container 2 (tap) 26 0
C
Dye scattered slower than in
hot water or faster than in
cold water
Container 3 (hot) 76 0
C
The dye scattered the fastest
in this container
Figure 1. Scattering of the dye among the three water samples
Q9. After putting drops of dye into the water, the dye scattered throughout the
water. But the rate of scattering of the dye differs in each container.
Q10. Hot water. Cold water.
Q11. The higher the temperature of the water, the faster the scattering of the dye.
Q12. The particles are moving fastest in the container with hot water. The particles
are moving slowest in the container with cold water.
Q13. The higher the temperature of the water, the greater the speed of the moving
particles.
Q14. The higher the temperature, the greater the kinetic energy of the particles.
Cold waterWater at
room temp
Hot water

33
Thermal Expansion
1. Explain how liquid thermometers work using the concept of thermal expansion.
2. Demonstrate the activity described or suggested in the module to explain thermal
expansion of solid.
3. Emphasize that objects or materials expand when heated and contract when
cooled. But emphasize also that different materials expand or contract to different
extents when heated or cooled.
4. If time permits, ask the students to research more on the applications of thermal
expansion to real life.
Phase Change
Teaching Tips
1. If the materials are available, some students may be allowed to use a heating
device like a burner, instead of hot water, to ‘heat’ the beaker of ice. Then they
can infer the difference in the amount of heat transferred to the ice based on the
melting time.
2. Students can be allowed to use an iron stand with clamp to hold the thermometer
to ensure that it will not touch the bottom of the container.
3. At this point, some guides in constructing graphs might be needed. Note that the
independent variable (heating time) is plotted along the horizontal axis while the
dependent variable (temperature) is plotted along the Y-axis.
4. Try out the activity first to determine the amount of ice that will allow the students
to finish their activity within the day. Discussion of results may follow during the
next session.
What happens when ice melts?
Activity
3.1

34
5. During the post activity discussion, give emphasis on the idea that it is not always
true that the energy transferred to an object or substance will cause a change in
the kinetic energy of particles.
Q15. The ice melts because the heat from the surrounding (higher temperature)
was absorbed by the ice (lower temperature).
Q16. The dependent variable is the ‘temperature’ while the independent variable is
the ‘time’.
Q17. Descriptions may vary depending on how the graphs of the students look like.
The accepted one should have a straight horizontal line like in the graph
shown in Figure 2 below (melting).
Q18. The temperature of the water while the ice was melting remains the same.
Q19. After the ice has melted the temperature of the water increases with time.
Figure 2
Melting
Vaporization
Temperature
Time
Heat
100°C
(Boiling point)
0°C
(Melting point) Ice
Water
Steam
(vapor)

35
Q20. Descriptions may vary depending on how the graphs of the students look like.
The accepted one must have a straight horizontal line like in Figure 2
(vaporization).
Q21. Both graphs have a straight horizontal line but the temperature level
corresponding to these lines differ.
After students learned about the relationship between the temperature of the
object and the amount of heat it can transfer, this time they will try to investigate on
their own the relationship between the mass of the object and the amount heat it can
transfer. In this activity, students are asked to plan and design their own
investigation, including the steps on how they will gather and analyze data to come
up with an answer to this question: How does the mass of an object affect the
amount of heat it can transfer?
Example:
Students may fill identical containers with different amounts of water of the
same temperature, say hot water. Then they pour both contents into two
containers with water of the same amount and temperature. Then they
measure the increase in temperature of water in both containers. The amount
of increase in the temperature of water can be related to the amount of heat
transferred to the object.
What is the relationship between the
mass of a material and the amount of
heat it can transfer?
Activity
4
What happens to the
temperature of water as it boils?
Activity
3.2

36
Teaching Tips
1. Make sure that the liquid samples are stored in the same room before the
experiment to ensure that they will be of the same room temperature when they
are used in the activity.
2. Aside from water and cooking oil, other samples of liquids can also be used.
3. If there are enough thermometers available, it is better to use a separate
thermometer for each liquid sample.
4. During the post activity discussion, provide the class with the table containing the
specific heat capacities of some materials. This will confirm their findings that
different materials have different heat capacities.
5. During the post lab discussion, include some real life applications of specific heat
capacity.
Q22. The water requires more time to increase in temperature.
Q23. The water requires more heat to increase in temperature.
Q24. The water has greater heat capacity.
Links
Chalfant, H., Peyron, M., Rachke, C. (2005, Fall). Heat and temperature. Sci Ed,
491. Retrieved from
http://www.biol.wwu.edu/donovan/SciEd491/HeatTempUnit.pdf
Expansion and contraction. (n.d.). Retrieved from
http://schools.cbe.ab.ca/b682/pdfs/Science%207/Heat-and-Temperature-
Unit3_T4_T6.pdf
Comparing heat capacities
Activity
5

37
How do voltage and resistance affect electric current?
What are the safety precautions needed in using electricity?
ELECTRICITY
In the previous modules, students learn about charges and how their charges
determine the forces that exist between them. In this module, they will study charges
as moving through conducting materials. Students will be dealing mostly on terms
like voltage, current and resistance in studying electricity. In the first activity, they will
determine how changing the voltage affects the current in an electric circuit. The
second activity deals with how resistance affects the current in a circuit. The next
activity talks about the two types of connection (series and parallel connections) and
how the charges flow in these connections. The last activity of this module deals with
the effects of too much current in the circuit on conducting materials, and how its
effect can be useful in practicing safety practices in using electrical appliances in
order to prevent accidents like fires or electric shock.
The topics covered in this module are relevant because of the applicability of
the lesson in preventing accidents like fires caused by unsafe use of electricity.
Current and Voltage
Electric charges can be made to move through a conducting material. The
electric charges are the electrons of the conducting materials. Materials such as
copper, steel, and aluminum have a lot of loosely held electrons which made them
good conductors of electricity. Current is a measure of the number of charges
passing through a cross-section of a conductor in a given time.
Unit 1
MODULE
4

38
What is the direction of current? A battery has terminal marks “+”and “-“. The
plus (+) sign indicates surplus or excess of charge and the negative (-) sign means
deficiency. The movement of charges from the positive side of the battery to the
negative side is called conventional current or simply current. However, this is not
the actual motion of electrons in a circuit. The direction of the flow of electrons is
from the negative terminal to the positive terminal. This is called electron current.
The direction of current does not affect what the current does.
An ammeter measures electric current. Because the device measures how
much charges flow in a certain cross section at a given time, it has to be connected
in series. Take note how the positive and negative signs of the ammeter and the
terminals of the battery are oriented as shown in Figure 1.
Figure 1. Ammeter connected in a circuit
Energy is needed to make the charges move. In Module 2, the students
learned that when work is done on an object, energy is transferred. The voltage of a
battery does the work on charges to make them move. Batteries are energy sources.
The chemical energy in the battery is transformed to electrical energy. This electrical
energy moves the charges in a circuit. The work done on the charges as it passes
through a load is measured as the voltage across the load.
A voltmeter measures voltage. The voltmeter must be connected parallel or
across the load as shown in Figure 2. The positive terminal of a voltmeter is
connected to the positive terminal of the bulb while the negative terminal is
connected to the negative terminal of the bulb as shown in Figure 2.

39
Figure 2. Voltmeter connected across the load
 In this activity, students will determine how voltage and current are related.
 Students will use voltmeters and ammeters to measure the current and
voltage in a circuit. Make sure that they follow the correct way of connecting
the ammeter and voltmeter. If the school cannot provide voltmeters and
ammeters, they can modify the activity by just relating the number of dry cells
or increase in voltage with the brightness of the bulb. The brighter the bulb,
the bigger the current.
 The dry cells must be connected in series which means the positive terminal
of one cell is connected to the negative terminal of the other.
 Ideally a switch must be included in the circuit so that they can turn off the
circuit to avoid wasting energy. The teacher can make an improvised switch
using illustration board and aluminum foil as shown in Figure 3.
Current and voltage
Activity
1
positive terminal
of the bulb
negative terminal
of the bulb

40
Figure 3. An improvised switch
 Be sure also to use new batteries for this activity especially when the
brightness of the bulb is being asked. For the bulb, use a flashlight with a
voltage rating of 2.5 V.
 In case no battery holders, use a cardboard to wrap two batteries tightly like a
cylindrical holder. Tape the cartolina to secure the tightness of the connection
of the batteries.
Answers to Questions:
Q1. (This will depend on the reading they get from the ammeter.)
Q2. The bulb glows brighter when two batteries are used.
Q3. (This will depend on the reading obtained in the ammeter.)
Q4. The current is higher for two dry cells as compared to one dry cell.
Q5. (This will depend on the readings obtained on the voltmeter.)
Q6. The bulb glows brighter.
Q7. This will depend on the readings obtained on the voltmeter.)
Q8. The voltage is bigger for two dry cells as compared to one dry cell.
Q9. For a constant load (one bulb), when the voltage increases the current also
increases.

41
Sample Data
No. of batteries Voltage (V) Current (A)
1 1.5 0.2 A
2 2.5 0.3 A
Activity 1 Discussion
The dry cell provides the energy that moves the charges in a circuit. The
dry cell must be connected by conducting wires to a load to form a complete circuit.
Adding dry cells in series increases the voltage in a circuit.
In the activity, adding dry cells increases the current in a circuit as shown by
the ammeter readings. The brightness of the bulb also indicates the amount of
current passing through it. The bigger the current through the bulb, the brighter it
glows. Both the meter readings and the brightness of the bulb show that voltage and
current are related. The activity shows that as the voltage increases, the current also
increases.
Current and Resistance
Another variable that can affect current is the resistance. As the term implies,
the resistance of the material opposes the flow of charges. Resistance can also be
measured and they are expressed in units called Ohms. A lower resistance would
mean that there is less opposition in the flow of charges and therefore bigger current.
Different materials have different amounts of resistance. Conductors
definitely have very little resistance and therefore allow more charges to pass
through. Insulators are materials that have very high resistance and therefore flow of
charges would be difficult.
The length and thickness of the conducting wire are factors that affect
resistance encountered by current. The longer the wire the greater will be its
resistance and the greater the cross sectional area (a measure of the thickness of
the wire), the lower will be its resistance.
The resistance of an object also changes when the object becomes wet. Dry
human skin for instance has a resistance of 100,000 ohms but when it gets wet its
resistance is reduced to 1,000 ohms. That is why it is important to dry the hands
when plugging an electrical appliance to reduce any chance of getting a lot of current
if an accident occurs.

42
Understanding the relationship between current and resistance is important in
protecting oneself from electric shock. The table below shows the physiological
effects that happen when a certain amount of current passes through the human
body.
Source: Department of Health and Human Services, Center for Disease Control and
National Institute for Occupational Safety and Health
In this activity, the students must be able to determine how resistance affects
the current through the circuit.
 The purpose of the activity is to find if a relationship exists between
current and resistance.
 If there is no ammeter available, the students can just compare the
brightness of the bulb since the brightness is also associated with the
current passing through them.
Current and resistance
Activity
2

43
 In the last part of the activity, the students were asked to connect the
ammeter at different points in the circuit. This is to show to them that
current is the same anywhere in the circuit.
Q10. The current decreases as the resistance increases or when the resistance
increases the current decreases.
Sample data:
Q11. The current reading at different points of the circuit is constant.
Q12. The readings indicate that current is the same anywhere in the circuit.
Electrical Connections
Series Connection
Circuit A in Activity 3 is a series circuit. In a series circuit, loads form a single
pathway for charges to flow. A gap or a break anywhere in the path stops the flow of
charges. When one bulb is removed from the socket, a gap is created. The other
bulb turns off as there is no longer current in the circuit.
The total resistance in a series circuit is equal to the sum of the individual
resistances of the load (bulb). Current is the same in every part of the circuit. The
current is equal to the voltage divided by the total resistance. As more load (bulb) is
added in a series circuit, the smaller the current as reflected by the brightness of the
bulb. The voltage across each load depends on the load’s resistance. The sum of
the voltage across each load is equal to the total voltage.
Parallel connection
Circuit B in Activity 3 is a parallel circuit. In a parallel circuit, loads form
branches; each provides a separate path for charges to flow. A gap or a break in any
branch will not affect the other branches. Thus, when one bulb is removed from the
No. of bulbs Current (A)
1 0.3 A
2 0.25 A
3 0.2 A

44
socket, a gap is created only for that branch. The other bulbs still glow as their path
is still complete.
In a parallel connection the voltage is the same across each load. The total
current is equal to the sum of the currents in the branches. The amount of current is
inversely proportional to the resistance of the load.
 In this activity students will find out how series and parallel connections
are constructed. Giving them a situation to figure out how to do it
stimulates problem solving skills of students.
 Be sure that when you let them do circuit A there should only be three
wires for each group. For circuit B only four wires should be given. If the
number of wires is not limited, they will not be able to execute the
simplest way to demonstrate connections of bulbs in series and parallel.
 Tell the class to show them what they have constructed and check if it fits
to the condition (one bulb unscrewed, then other one turns off for Circuit
A; one bulb is unscrewed and the other bulb remains lighted for Circuit B).
Usually the series connection is easier for the students. For parallel
connections, students will experience some challenge in doing it.
 Most textbooks show parallel connections shown in Figure 6:
Figure 4 A parallel circuit
What’s the connection?
Activity
3

45
However, students might have another way of connecting the bulbs and
these possible outputs shown below are also in parallel.
Figure 5 Parallel circuits
 In the last part of the activity, the students were asked to measure the
voltage across the two bulbs and the voltage drop across each bulb in
circuits A and B. Sample data is shown below:
Table 3
Circuit Voltage drop (V) Voltage across the
two bulbs (V)
Bulb 1 Bulb 2
A 1.5 1.0 3
B 2.5 2.5 3
Circuit A shows that the voltage of the dry cell is divided between the two
bulbs. The voltage depends on the resistance offered by the bulbs. If the bulbs are
identical, the measurement should be the same.
Circuit B shows that the voltage across each bulb is almost equal to the
voltage of the dry cells. This shows that in this type of connection, voltage is the
same across any two points in the circuit.
Q13. There is only one path for current in Circuit A.
Q14. Because there is only one pathway for the current, when one bulb is removed
from the holder, it made a gap or a break in the path. A gap or a break
anywhere in the path stops the flow of charges. All bulbs connected will go
out.

46
Q15. There are two paths for current in Circuit B.
Q16. Since only the path of the unscrewed bulb has the gap, the other bulb shines
because its path is complete. The current can still pass in the path of the bulb
with a complete pathway.
Q17. Circuit B has brighter bulbs.
Q18. The current in Circuit A becomes smaller as more bulbs are added because
the bulbs glow dimmer. The brightness of the bulbs in Circuit B remains the
same as bulbs are added in the circuit. The current in Circuit B is bigger than
in Circuit A.
Safety in Using Electricity
Fires can happen when the wires start heating up causing combustible parts
of the house to be set on fire. The wires heat up when the current passing is more
than what the wires can carry. In this case there is an overloading of the circuit. An
example of how the circuit gets overloaded is by plugging a lot of appliances in a
common outlet like an extension cord.
Another instance of overloading of the circuit is the presence of short circuits.
Short circuits happen when wires with defective rubber insulation touch each other
so the current does not pass to the supposed path it should take. It is a circuit where
the current encounters very little resistance and therefore the amount of current will
increase rapidly. Such increase in the amount of current leads to the overloading of
the circuit and can lead to fires.
But why do wires heat up when there is too much current? In the wires the
electrons that flow in a closed circuit collide with the atoms of the conducting wire. As
the collisions take place the kinetic energy of the metal atoms increases. The
increased kinetic energy of the atoms is dissipated as heat. You learn in the module
on heat that temperature is related to the kinetic energy of the moving particles. The
higher the kinetic energy of the particles, the higher will be its temperature. The
higher the current passing through the wire, the more collisions between the
electrons and the atoms of the wire take place. In the end the wire will become hot.
So just imagine how much heat will be generated from an overloaded circuit.

47
 There are two tasks in Activity 4. The first part shows how increasing the
current can cause the wires to heat up. The second task shows how a short
circuit happens.
 The fine copper wire to be used can be obtained from stranded electric wires.
Remove the rubber insulation and get these fine copper wires for this activity
Figure 6 Strands of copper wires
 The first task shows the wire heats up melting the candle. The hotter the wire
the deeper will be the cut made on the candle.
 The second task is a simulation of a short circuit. Supervise the students
making sure that they don’t let touching of the exposed parts of the wire take
too long as the wires get hotter afterwards.
Q19. The candle touching the wire melts.
Q20. The current in the circuit increases.
Q21. Heat is produced along the wire. The bigger the current in the circuit, the wire
becomes hotter, and the more the candle will melt.
Q22. The light goes off when the wires touch each other.
Stay safe!
Activity
4

48
Q23. The current took the path of the exposed part of the wire touching each other.
Q24. The resistance encountered in the short circuit where the charges flowed is
lower.
Q25. The current in the short circuit increases.
Q26. Short circuits cause fire when the nearby materials near the wires becomes
so hot and starts to burn.
Q27. Resistance decreases as more appliances are connected to one outlet.
Q28. The total current increases.
Q29. Overloading the circuit can make the wires hot setting combustible materials
on fire.
Henderson, Tom. (21 January 2013). Retrieved from
http://www.physicsclassroom.com/class/energy/
Hewitt, P.G. (2002). Conceptual physics. USA: Prentice-Hall, Inc. Saddle River, New
Jersey.
Kirkpatrick, L.D. and Wheeler, G.F. (1998).Physics a world view. USA: Saunders
College Publishing
Ostdiek, V.J.and Bord, D.J. (1987).Inquiry into Physics. USA: West Publishing
Company
DepEd.Science and Technology IV.SEDP Series. (1992). Philippines: Book Media
Press, Inc.
http://www.allaboutcircuits.com/vol_1/chpt_3/4.html

49
SOUNDS
This unit deals with the propagation of sound through solid, liquid, and gas. In
the course of discussion, wave characteristics and properties particularly reflection
and refraction will be taken into account. From the activities, students will be able to
identify also the factors that affect the speed of sound.
At the end of the unit, students should be able to:
1. compare the speed of sound through solids, liquids and gases;
2. infer how the molecular structure of a material affect speed of sound
moving through it; and
3. investigate the effect of temperature on speed of sound through fair
testing
Unit 1
MODULE
5
1. Sounds can be produced without using any material objects.
2. Hitting an object harder changes the pitch of the sound produced.
3. Sounds can travel through empty space (a vacuum).
4. Sounds cannot travel through liquids and solids.
5. Sound travels slower in less dense medium.
6. The greater the density of the medium the faster the sound is
transmitted.

50
WORKSHEET 1: Solids, Liquids, and Gases
Direction: Using several resources and references, compare the different
characteristics of solids, liquids and gases by completing the table below:
Comparing Solids, Liquids, and Gases
Characteristics Solid Liquid Gas
Intermolecular
spacing
very close Slightly farther Far from one
another
Volume Has definite shape Takes the shape
of the container
Takes the shape
of the container
Ability to flow Cannot flow Able to flow Able to flow
Compressibility Not compressible Not compressible Highly
compressible
Density densest dense Low density
Teaching Tips
Motivation
The facilitator may start with the popular songs of popular artists like
maroon 5, Justin Bieber, and Taylor Swift. Students may be asked to sing
some of the popular tunes and ask them who are fond of watching
concerts. Also ask them why concerts are usually done during night time
and not during day time. Probe further until the concept of sound as a
wave is deduced.
On which medium does sound travel fastest? Solid, Liquid, or Gas?
How does the temperature of the medium affect the speed of sound?
How are reflection and refraction manifested in sound?

51
Facilitating Learning
1. Introduce Activity No. 1 to arrive at the objectives: (1) to infer that sound
waves are vibrations that travel through the air and (2) to infer that sound
is transmitted in air through vibrations of air particles.
2. Since Activity No. 1 includes two parts, emphasize the focus of each part
so as to guide the students while on task.
3. Data processing may be done by group presentation and class discussion
of the guide questions to probe the concept that sound waves are
vibrations that travel through the air and that sound is transmitted in air
through vibrations of air particles.
4. Discussion should also be extended to cover the differences and
similarities of longitudinal and transverse waves and introduction to the
characteristics of longitudinal waves.
5. Then introduce Activity No. 2: Characteristics of Waves: Comparing
Longitudinal Waves and Transverse Waves. In this activity the students
will use a metal slinky to (1) distinguish the different characteristics of
waves; (2) determine the frequency and wavelength; and (3) compute the
wave speed based on the frequency and wavelength.
6. Data processing may be done by group presentation. Class discussion of
the data in tabular form and guide questions to the characteristics waves.
7. Extend the discussion to emphasize that sound waves are also called
pressure waves. From here, introductory discussion on factors affecting
sound may be included.
8. Then introduce Activity No. 3: Sound Race…Where Does Sound Travel
Fastest? In this activity the students should be able to distinguish which
material transmits sound the best.
9. Data processing may be done by group presentation and class discussion
of the data and results in tabular form and guide questions to speed of
sound in different media.
10. Extend the discussion to include characteristics of other media like
solids and liquids then let them do worksheet 1 and Activity No. 4:
Chimes...Chimes...Chimes... In this activity, they will have to design
their own chime and use this chime to determine how density of the
material or medium affects the speed of sound.

52
11. Ask where does sound travel faster? In hotter medium or cooler
medium? Introduce Activity No. 5: Faster Sound...In Hotter or Cooler?
In this activity the students will be able to determine how temperature
affects the speed of sound.
12. Extend the discussion to include calculation of the speed of sound with
respect to the temperature of the medium. Let them do Worksheet No.
2.
13. Summarize Lesson 1 by going back to the key questions particularly
questions 1 and 2.
14. Use the question posted in the motivation to introduce the concept of
properties of sound. Then introduce Activity No. 6: Reflecting and
Refracting Sound...
15. Data processing may be done by group presentation and class
discussion of the data and results in tabular form and guide questions to
refraction and reflection of sound waves.
16. Extend the discussion to include practical application of sound reflection
and refraction.
17. Summary of the whole module may be probed by asking the 3rd
key
question and by asking for insights and experiences they had during the
preparation, presentation and post-presentation discussion of their
outputs.
In this activity, students will be able to infer that sound is KE of vibrations that
travel through the air; and sound is transmitted in air through vibrations of air
particles.
Answers to Questions:
Q1. The salt bounced up and down.
Q2. When the small can is tapped loudly or forcefully.
The dancing salt and the
moving beads!
Activity
1

53
Q3. Sound was produced when the small can is tapped. Yes the salt bounced up
and down the plastic top while tapping the small can.
Q4. The sound produced in the small can made the plastic top of the large can
vibrate making the salt bounce up and down.
Q5. Sound waves are vibrations of air particles.
Q6. The rock salt bounced higher the loudness of the sound is increased.
Q7. The amplitude of the wave.
Q8. The other colored beads collided with the blue bead.
Q9. Yes
Q10. Yes
Q11. Sound wave is classified as a longitudinal wave.
In this activity, students will be able to distinguish the different characteristics
of waves; determine the frequency and wavelength; and compute the wave speed
based on the frequency and wavelength)
Q12. frequency
Q13. Wavelength is decreased provided the speed of shaking or disturbing the
medium is the same or constant.
In this activity, students will be able to distinguish which material transmits
sound the best.
Sound race... Where does
sound travel fastest?
Activity
3
Characteristics of waves: Comparing
longitudinal and transverse waves
Activity
2

54
Q14. Yes / Yes/ Yes
Q15. Yes / Yes / Yes
Q16. Wood/Water/Metal/Metal
Q17. The sound seems louder in the string as compared to air.
Q18. Yes
Q19. Yes
In this activity, students will be able to infer using improvised chimes that
closely spaced particles of the medium are best transmitters of sound.
Q20. Chime 2
Q21. Chime 2/Chime 2
Q22. Chime 3
Q23. Chime 3 / Chime 3
Q24. The chime with packed string objects produces sound that reached the
farthest distance.
Q25. Chime 3
Q26. The more closely distanced the stringed objects in the chime, the better the
sound is transmitted.
Chimes...Chimes...Chimes...
Activity
4

55
In this activity, students will be able to be able to determine how temperature
affects the speed of sound.
Q27. HOT cylinder
Q28. HOT cylinder
Q29. HOT cylinder
Q30. HOT cylinder
Q31. The higher the temperature, the faster the sound travels.
In this activity, students will be able to be able to observe how longitudinal
waves reflect and refract.
Q32. The compressions or rarefactions bounce off after hitting the wall
Q33. No they are not found on the same positions
Q34. Sound will also bounce off when it strikes a fixed end or the wall
Q35. The frequency of the wave increases
Q36. Increase in frequency of the sound is manifested as change in pitch
Q37. Amplitude increases
Q38. Louder sound is observed
Q39. Faster waves
Reflecting and refracting sound
Activity
6
Faster sound... In hotter or cooler?
Activity
5

56
Links
Cheung Kai-chung (Translation by Yip Ying-kin). (2013). Why do sound waves
transmit farther at night? Is it because it is quieter at night? Retrieved from
http://www.hk-phy.org/iq/sound_night/sound_night_e.html
Keith Gibbs. (2013). The refraction of sound in hot and cold air. Retrieved from
http://www.schoolphysics.co.uk/age11-
14/Sound/text/Refraction_of_sound/index.html

57
COLORS OF LIGHT
This unit is concerned with the demonstration of understanding of some
properties and characteristics of light. Among the characteristics and properties of
light, we focus on refraction and specifically dispersion of light. We will try to find out
through simple activities on how light disperse to form the colors of light. We will also
try to find the hierarchy of colors of light in terms of frequency, wavelength, and
energy. The different activities provided in this module will make us realize the
beauty of everything with light.
At the end of the unit, students should be able to:
1. demonstrates the existence of the color components of visible light using
a prism or diffraction grating;
2. infers that color is a manifestation of visible light’s frequency or
wavelength;
3. explains that red is bent the least and violet is bent the most according to
their wavelengths or frequency; and
4. explains the hierarchy of colors in relation to energy.
How are refraction and dispersion demonstrated in light?
In the different colors of light, which is bent the most and the least?
Why do we see spectacular events in the sky like rainbows, red sunset and
blue sky?
Unit 1
MODULE
6

58
Description of Activities
 Activity 1: The colors of the rainbow...The colors of light
(The students will be able to infer that white light is made up of many different
colors of light and each of these colors of light bends differently.)
 Activity 2: Red versus violet…
(Students will be able to infer that violet light bends more than red light when
dispersed; and bending depends on the refractive index, frequency and
energy of the color of light.)
 Activity 3: Which color has the MOST energy?
(Students able to infer that the energy of the colors of light increases as one
goes towards the right side of the color spectrum and red light has the least
energy and blue light has the most energy.)
 Activity 4: The color spectrum wheel revisited
(Students will be able to infer that light is composed of colors of light of
different frequencies and wavelengths; the frequencies of the colors are
inversely proportional the wavelength; the product of frequency and
wavelength of the colors of light is a constant; and the arrangement of colors
of light shows the hierarchy of the color’s corresponding energy.)
 Activity 5: Scientific explanations behind certain beliefs
(Students should be able to come up with a presentation of the scientific
explanations of certain superstitious beliefs related to observable phenomena
in the sky.)
Teaching Tips
Motivation
The facilitator may introduce a character named Roy G. Biv. Ask students
whether they are familiar with the character. Ask them also if there is a
connection between the character and the lessons. Ask the students if they
could guess some information or concept from the name of the character. If
the students recognize the colors of light then ask key question no. 3. Follow
it up by the first two key questions.

59
Facilitating Learning
1. As a brief review, introduce the concept of apparent depth and the
concept of refraction of light.
2. Introduce the concept of dispersion as a special kind of refraction. Let
them perform Activity 1 which will give students more information about
how visible light refracts in different optical densities resulting to different
colors of light. This activity is composed of two parts. One makes use of
locally available materials while the other makes use of the standard
materials like prism and artificial source of light. A comparison of the two
may be highlighted during the discussion of results.
3. The facilitator may let the students present their outputs per group and
processing be done after all the groups have presented by culling ideas
and concepts from the presented data and probing students to arrive at
the concept of colors of light.
4. The facilitator may ask why a certain hierarchy of colors of light is
observed. Then introduce Activity 2 and let the students perform the
activity to determine which is really more bent: the red light or the violet
light. This will be explicitly described by the students during the
processing when they present their outputs which would include the
relation of the bending and the index of refraction of the color of light.
5. The facilitator may let the students present their outputs per group and
the concept that blue is bent more or violet is bent more than red light.
6. Then ask the students which color of light gives the most energy. Let
them predict – red or violet light. Let them perform Activity 3. The
facilitator may let the students present their outputs per group and
the concept that blue or violet has the highest energy and red has the
least.
7. Then ask the students on which other characteristics does energy of
colors depend on to introduce Activity 4. This activity was already done in
Grade 7. The focus of the activity in Grade 7 was to identify the
corresponding frequency and wavelength of each color of light and the
computation of the speed of each of the colors of light. This time the focus
is on how energy relates to the frequency of the colors of light. From the

60
given materials, students will be able to determine the relationship
between frequency and the energy of the colors of light.
In preparation for Activity 4, reproduce several copies
(preferably colored) of the patterns of the spectrum wheel found
in pages 107-108 of the Learner’s Module. Then paste the
patterns on pieces of cardboard to make them stronger and
more durable. Distribute the spectrum wheel patterns to the
students only during the activity proper then collect them
afterwards so that the next group of students will be able to use
them as well.
8. Then ask them some inferences on how rainbows are formed. Ask them
also some superstitious beliefs that the students are familiar with in
relation to the existence of rainbows.
9. Let them identify all the major concepts they were able to grasp from all
the activities to build a concept on how rainbows are formed. Then let
them do Activity 5.
10. Let the students present their outputs per group. Then go back to the
key questions to be able to summarize the concepts on visible light.
Q1. Red, Orange, Yellow, Green, Blue, Violet
Q2. From Top to Bottom: Red, Orange, yellow, Green, Blue, Violet
Q3. The refractive index of prism varies with the wavelength or color of the light
used. This causes the different colors of light to be refracted differently. Then
leave the prism at different angles, creating an effect similar to a rainbow
Q4. Some colors visible in the prism were not observed in the water
Q5. Small value for refractive index is observed in red and large refractive index for
violet
The colors of the rainbow...
The colors of light
Activity
1

61
Q6. The refractive indices of the different colors of light indicate that light of different
colors travels at different speeds in the prism which accounts for the different
amounts of bending. Thus, blue light with greater refractive index refracts more
and appears at the bottom of the red light
Q7. Yes
Q8. Red, Orange, Yellow, Green, Blue, Violet
Q9. Blue
Q10. The greater the angle of refraction, the greater is the refractive index and
more bending is also observed.
Q11. Red
Q12. Violet
Q13. Violet
Q14. Red
Q15. Red/ Violet
Which color has the MOST
energy?
Activity
3
Red versus violet
Activity
2

62
Q16. Violet, Violet
Q17. Red, Red
Q18. The wavelengths and frequencies of the colors of light vary. The wavelength
decreases from red to violet while the frequency increases from red to violet.
Q19. The products of frequencies and wavelengths of the colors of light are equal
or the same.
Q20. Yes
Q21. As the frequency of the color of light increase, the energy also increases. Red
has the least frequency with the least energy and Violet has the highest
frequency and the highest energy.
Q22. The higher the frequency of the color of light, the greater is its energy.
Hewitt, Paul. (1989). Conceptual physics (6th
Ed.) London: Scoot, Foresman and
Company
Hwang, Fu-kwun. (n.d.). Colors. Retrieved from http://users.hal-
pc.org/~clement/Simulations/Mixing%20Colors/rgbColor.html
Georgia State University. Department of Physics and Astronomy. (2013). Retrieved
from http://www.phy-ast.gsu.edu.
Release the rainbow. (2013). Retrieved from
http://www.optics4kids.org/home/futurescientists/easy/release-the-rainbow/
Tracing, R. (n.d.). S369 AP physics. Retrieved from
http://www.shs.d211.org/science/faculty/MJP/s369/light/docs/RayDiagrams.htm
The color spectrum wheel
revisited
Activity
4

Teacher guide grade 8

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