The document is a lesson on work, energy, and power for junior high school physics, detailing the definitions and relationships between these concepts. It explores various forms of energy, the work-energy theorem, and the laws governing energy transformations and conservation. It also includes various calculations and practical scenarios to illustrate the principles of work, energy, and power.

1. Lesson 2:
Work, Energy, Power
Junior HIGH SCHOOL DEPARTMENT
Science (Physics)
Prepared by: Mr. Simon Peter Familara

2. What is Energy?
What are the forms of Energy?
What is Work?
How are energy and work relate together?

4. Work is
The measure of energy transfer that occurs when an
object is moved over a distance by an external force at
least part of which is applied in the direction of the
displacement.
W = Fd
d = displacement F = Force

7. Unit Conversion to Joules
British Thermal Unit (BTU) 1055.06 Joule
1 erg 10-7 Joule
1 horsepower-hour 2684519.5377 Joule
1 foot-pound 1.36 Joule
1 Kilo-watt hour 3.6 million Joule
1 Newton-meter 1 Joule

9. Work is done to transform energy from one form
to another.
When lifting and dropping a rock:
● You do work to store Potential Energy (PE)
as you apply a force to lift a rock a distance
(height).
● Gravity does work converting potential
energy (PE) to kinetic energy (KE) while the
rock falls.

10. Work done is positive if there is positive displacement is in
direction of applied force.
For e.g. if you push a cart and it moves forward.
It is negative when there is negative displacement in
direction of applied force.
For e.g. the work done by frictional force against a moving
body.
It is zero if there is no unbalanced force applied or if there is
no displacement in the direction of applied force.
For e.g, when you try to move a large rock but fails.

11. A 10 kg object experiences a horizontal force which
causes it to accelerate at 5 m/s2
, moving it a distance
of 20 m, horizontally. How much work is done by the
force?

12. F = ma = (10)(5) = 50 N.
d = 20 m,
W = Fx = (50)(20) = 1000 Joules

13. How much work is done by
the stickman that pushes a
box 5 meters with a force of
12 Newtons forward?

14. A student lifts a physics book applying a
force equal to is 10 N weight a distance of
3 m up. How much work did the student
do on the book?

16. How much work is done when a force
of 50 N is applied but does not move a
box?

18. Sergio pushed a box with 50 N of force forward. When it did not
move he pushed the box even harder with 100 N of force but the
box still did not move. When did Sergio do more work?
A) When he applied 50N of force
B) When he applied 100N of force
C) Neither

19. C) Neither : Movement in the
direction of force must occur or
no work is done

20. BASIC TRIGONOMETRY

24. When a force F and the displacement d are not parallel to
each other, only the component of the force parallel to the
displacement does work. If θ is the angle between th
directions of F and d, the magnitude of the component of
F parallel to d is Fcosθ . The work done is
W=Fd(cosθ )

26. Energy
Energy is defined as the “ability to do work,
which is the ability to exert a force causing
displacement of an object.” Despite this
confusing definition, its meaning is very simple:
energy is just the force that causes things to
move. Energy is divided into two types:
potential and kinetic

29. Forms of Energy
Different forms of energy we have in nature include:
Work is done when transforming one form to another

31. Law of conservation of energy
The law of conservation of energy states that energy can neither
be created nor destroyed - only converted from one form of energy
to another. This means that a system always has the same amount
of energy, unless it's added from the outside. This is particularly
confusing in the case of non-conservative forces, where energy is
converted from mechanical energy into thermal energy, but the
overall energy does remain the same. The only way to use energy is
to transform energy from one form to another.

32. Entropy
Entropy is a measure of the disorder of a system. Entropy also
describes how much energy is not available to do work. The more
disordered a system and higher the entropy, the less of a system's
energy is available to do work.

34. PE = Fd

35. Work to Store Gravitational Potential
Energy (GPE)
● Gravitational potential energy (GPE)
equals weight of an object times the
height it is lifted
● When given a weight and height: GPE =
Fwh
● When given a mass and height GPE =
mgh
● g = 10 m/s2

38. How much gravitational potential energy
do you have when you lift a 15 N object 10
meters off the ground?

42. How much potential energy is stored when a
force of 50 N is applied over 0.5 meter in the
string of a bow?

43. E

47. Kinetic energy is energy in motion. The velocity
of an object is very important in determining its kinetic
energy. The formula for kinetic energy is as follows:
Kinetic energy and mass Is directly related. Kinetic
energy and velocity is also but has an exponential
effect because it’s squared.

48. Work Done to Stop Motion
Work is also done to stop and
object from moving and would be
equal to kinetic energy (KE) we will
see later in this page.
Work = Fd and KE = ½ mv2
Work = KE

52. How much kinetic energy is in a 2111 kg
ford F-150 going 30 m/s down the
highway?

53. 949,950 J

54. How much force is required by the breaks to stop
2111 kg ford F-150 going 30 m/s down the
highway in 15 meters?
63,330 N

55. Power
Power is the rate at which work is done
● The unit of power is the watt (W)
● A watt equals a joule per second
Power is calculated as work divided by time. If you have force,
distance, and time you can use the substituted formula you see here.
Power = Work / time or P = W / t

57. A car does 2450-J of work in 8 seconds.
What is the power of the car?

59. Joe can go up a flight of stairs in 15
seconds. If the physics teacher weighs
850 N and the vertical height of the
stairs is 10 m, what is Joe’s power
output?

61. Recap:
● Work is the product of force and displacement in the direction of the
force.
● Energy is the ability to do work. It is expressed in joules or ergs
● The potential energy due to position is called gravitational potential
energy.
● The potential energy when the body is stretched or compressed is called
the elastic potential energy.
● The work-energy theorem states that the net work done on an object
causes a change in the kinetic energy of an object,
● Power is the rate of doing work. Its SI unit is watt

62. Write the all the formulae for Force, Work,
Energy and Power on a 1/2 Index Card. This
would be your legal “Kodigo” during
assessments and summative test.

63. Case Analysis:
Group yourselves into two groups. Read the case uploaded in the Google
Classroom, then
Discuss among your group about how to differentiate renewable and
nonrenewable sources of energy. How energy from different sources
transformed into other forms for specific uses and application? What are
the ways to conserve energy?
Write a written report as a group about what you've discuss, and upload it to
Google Classroom.

64. References:
https://stickmanphysics.com/
Exploring Life Through Science Series: Grade 8
Science for Innovative Minds : Grade 8