1. Chapter 4 Section 1 Energy
Page

2. Energy Definition Energy is the ability to cause change ????
Energy is the ability to do work.
Work is moving something against a force.
Force and distance
If we lift a block of metal from the floor to this table, we have done work on the block.
What is the force?
If we push a box across the floor we do work.
What is the force

3. Different Types of Energy
Mechanical
Electrical
Chemical
Sound
Light
Thermal (heat)
Nuclear

4. Energy Conversion Chemical Energy to Mechanical Energy
Burn gasoline in a car to make it go
Chemical Energy to Electrical Energy
A battery supplies power to a cell phone
Electrical Energy to Light Energy - ?
Electrical Energy to Sound Energy - ?
Electrical Energy to Mechanical Energy-?
Chemical energy to Thermal Energy
Electrical Energy to Thermal Energy

5. Kinetic Energy
The energy something has as a result of its motion
KE = ½ m v2
m = mass v = velocity
v = 1 m/s v2= 1 m2/s2
v = 2 m/s v2= 4 m2/s2
v = 3 m/s v2= 9 m2/s2
v = 4 m/s v2= 16 m2/s2
v = 5 m/s v2= 25 m2/s2

6. Energy Units Energy is the same as work KE= ½ m v2 W = F d
m in kg, v in m/s so v2 is m2/s2
or (kg m/s2 )* m or N * m called a joule
W = F d
F: Newtons Kg m/s2
d : meters m
W : N m called a joule
Kg m2 / s2 called a joule J

7. Practice Problems – Kinetic Energy (Page 102: 1,2,3)
A jogger with a mass of 60.0 kg is moving at a speed of 3.0 m/s. What is the jogger’s kinetic energy?
Given:
Asked:
Formula: KE = ½ mv2
Substitute
Answer:

8. Page 102 Problem 1
A baseball has a mass of 0.15 kg is moving at a speed of 40 m/s. What is the baseball’s kinetic energy
Given:
Asked:
Formula: KE = ½ mv2
Substitute
Answer:

9. Page 102 Problem 2
A sprinter has a mass of 80.0 kg and a kinetic energy of 4,000 J. What is the sprinter’s speed?
Given:
Asked:
Formula: KE = ½ mv2
Substitute
Answer:

10. Page 102 Problem 3
A car with a mass of 1,500 kg doubles its speed from 50 km/hr to 100 km/hr. By how many times does the kinetic energy of the car increase?
Given:
Asked:
Formula: KE = ½ mv2
Substitute
Answer:

11. Potential Energy Energy that is stored (available to do work)
Examples
Elastic potential energy – stored in a spring
Chemical potential energy – stored in a battery
Gravitational potential energy- stored by an object due to its position above the Earth’s surface

12. Gravitational Potential energy
The energy we store in an object when we lift it above the earth.
GPE is equal to the work we do in lifting an object
work= Force x distance= Fg x h
work = weight times the height
Since Fg = mg and height is the distance moved
GPE = work done= mass x g x height
GPE= mgh kg x m/s2 x m = kg m2/s2

13. Practice Problems- Potential Energy Page 104: 1,2,3, 4EC
What is the gravitational potential energy of a ceiling fan that has a mass of 7.0 kg and is 4.0 m above the ground?
Given:
Asked:
Formula: GPE = mgh
Substitute:
Answer:

14. Page 104 Problem 1
Find the GPE of a coffee mug with a mass of 0.3 kg that is on a counter top 1m above the ground.
Given:
Asked:
Formula: GPE = mgh
Substitute:
Answer:

15. Page 104 Problem 2
How high above the ground is a baseball with a mass of 0.15 kg and GPE of 73.5 J?
Given:
Asked:
Formula: GPE = mgh
Substitute:
Answer:

16. Page 104 Problem 3
A rock climber is 200m above the ground and has a GPE of 117,600 J. What is the rock climber’s mass?
Given:
Asked:
Formula: GPE = mgh
Substitute:
Answer:

17. Page 104 Problem 4
Suppose the mass of an object and it’s height above the ground both were doubled. How much would the object’s GPE change?
Given:
Asked:
Formula: GPE = mgh
Substitute:
Answer:

18. Different Types of Energy
Mechanical
Kinetic Energy- due to motion
Gravitational Potential Energy- due to position
Electrical
Chemical
Sound
Light
Thermal (heat)
Nuclear

19. Changes in Gravitational Potential Energy (page 105)
2 meters
2 meters
2 meters
2 meters
2 meters

20. Conservation of Energy Section 4:2 Page 107

21. Energy Transformation (P107)

22. Light Bulb Purpose is to convert electrical energy to light energy
But, also bulb gets hot so we know that some of the energy has been converted to thermal energy (heat)
Heat is wasted because the purpose is light
Fluorescent bulbs produce less heat so they are more efficient.
What are some other devices that convert electrical energy to some other form?

23. Energy Conversion Chemical Energy to Mechanical Energy
Burn gasoline in a car to make it go
Chemical Energy to Electrical Energy
A battery supplies power to a cell phone
Electrical Energy to Light Energy - ?
Electrical Energy to Sound Energy - ?
Electrical Energy to Mechanical Energy-?
Chemical energy to Thermal Energy
Electrical Energy to Thermal Energy

24. Chemical to Heat to Mechanical

25. Automobile Piston Gas fumes and air are combined under pressure.
Spark from the plug ignites the fuel/air mixture.
Explosion exerts pressure pushing the piston back down.
Changes chemical energy to heat energy to mechanical energy.
A lot of energy is lost to heat so we have a cooling system to remove this heat.

26. Conservation of Mechanical Energy
Kinetic Energy is energy due to motion of an object.
KE = ½ m v2
Potential energy is the energy due to position above the earth.
PE = mgh
Total Mechanical energy = KE + PE – wasted energy

27. Energy of a Projectile Thrown (or hit) horizontally
Thrown (or hit) straight up
Thrown (or hit) up at an angle

28. Read Page 110

29. Cursive Writing
I hereby agree to the conditions set forth in the test regulations and certify that I am the person whose name, address, and signature appear on the answer sheet.
Name

30. Swing Energy (P110) PE = maximum KE = 0 PE = maximum KE = 0
PE = minimum
KE = maximum

31. BUT
Will a swing swing forever?

32. Law of Conservation of Energy
Energy cannot be created or destroyed.
Energy changes form but is not created or destroyed.
Total amount of energy in the universe does not change.
We can add energy or take away energy from a small part of the universe.
Energy in = energy out
Hair Dryer (P111)

33. Swing Energy (P110) GPE = maximum KE = 0 TME= GPE+KE GPE = ? KE = 0
mass = 2 kg
14 meters
TME= GPE+KE
GPE = ?
KE =
2 meters
Ground

34. Useless Energy
As the swing moves, air resistance and friction convert some of the kinetic energy into thermal energy.
The loss of thermal energy causes the swing to gradually slow down and stop.

35. Nuclear Energy (page 113)
Prior to Einstein there were two separate laws
Conservation of Energy
Conservation of Mass
Einstein E= mc2
Mass can be converted to energy and energy can be converted to mass
Nuclear Fission
Nuclear Fusion

36. Fission (splitting)
energy
0n1
38 Kr93
92 U235
0n1
0n1
54Xe140
0n1

37. Fusion (joining)
1H3
1H2
2He3

38. Chapter 4 Assignments Page 102: 1-2-3 Page 104: 1-2-3-4EC
Practice Problem Handout
Pendulum Lab- Monday 10/21
Note Taking Work Sheet Tue 10/22
Chapter 4 Review: 1-12, Wed 10/23
Chapter 4 Test Thursday 10/24

39. Practice Problems
Find the kinetic energy of a ball with a mass of 0.75 kg moving with a speed of 50 m/s?
Find the gravitational potential energy of a 80 kg diver on top of a 10m high diving tower?
If the diver jumps off the tower, what is the GPE of the diver half way down to the water?
If the diver’s kinetic energy is 3920 Joules when he is half way down, what is his velocity?
What will be the velocity of the diver just as he hits the water? HINT: What will h = ?

40. Practice Problem 1 Find the kinetic energy of a ball with a mass of 0
Practice Problem 1 Find the kinetic energy of a ball with a mass of 0.75 kg moving with a speed of 50 m/s?
Given:
Asked:
Formula:
Substitute:
Answer

41. Practice Problem 2 Find the gravitational potential energy of a 80 kg diver on top of a 10m high diving tower?
Given:
Asked:
Formula:
Substitute:
Answer

42. Practice Problem If the diver jumps off the tower, what is the GPE of the diver half way down to the water?
Given:
Asked:
Formula:
Substitute:
Answer

43. Practice Problem 4 If the diver’s kinetic energy is 3920 Joules when he is half way down, what is his velocity?
Given:
Asked: units
Formula:
Substitute
Answer with units:

44. Problem 5
What will be the velocity of the diver just as he hits the water? HINT: What will h = ?
Given:
Asked: units
Formula:
Substitute
Answer with units:

45. Chapter 4 Assignments
Clear Desks except for calculator and Reference Sheet
Write this formula on your Reference Sheet
Total Mechanical Energy = KE + GPE
Turn in homework before you leave
Page 102: 1-2-3
Page 104: EC
Practice Problem Handout
Pendulum Lab
Note Taking Work Sheet
Chapter 4 Review: 1-12, 22-25

46. Problems Given: Asked: Units
Formula: KE = 1/2mv2 , GPE= mgh, TME=KE+PE
Substitute:
Answer: