1. Chapter 15
Energy

2. Energy is the ability to do work
Work and energy are closely related. When work is done on an object, energy is transferred to that object.
Energy is the ability to do work
Work is a transfer of energy
Work and energy are typically measured in joules

3. Energy is classified into two general types:
Kinetic Energy
2. Potential Energy

4. Kinetic Energy
Kinetic comes from the Greek work kinetos, meaning “moving”
Kinetic energy of a moving object depends upon its mass and speed 1
mv2
Kinetic Energy = 2

5. 1
A 70.0 kilogram man is walking at a speed of 2.0 m/s. What is his kinetic energy?
mv2
KE = 2 1
KE =
(70.0 kg) (2.0 m/s)2 2 1
(70.0 kg) (4.0 m2/s2)
KE = 2
KE =
140 kg x m2/s2 or Joules

6. 1
A 1400 kilogram car is moving at a speed of 25 m/s. How much kinetic energy does the car have?
KE =
mv2 2 1
(1400 kg) (25 m/s)2
KE = 2 1
KE =
(1400 kg) (625 m2/s2) 2
KE =
437,500 kg x m2/s or 437,500 Joules

7. Energy that is stored as a result of position or shape
Potential Energy
Energy that is stored as a result of position or shape
Two forms of potential energy are:
Gravitational potential energy
Elastic potential energy

8. Gravitational Potential Energy
Potential energy that depends on an object’s height is called gravitational potential energy
Gravitational PE Depends on the object’s mass, height, and acceleration due to gravity.
Potential Energy (PE) = mgh

9. A diver at the top of a 10.0 meter-high diving platform has a mass of 50.0 kilograms. What is her potential energy relative to the ground?
PE = mgh
PE = (50.0 kg) ( 9.8 m/s2) (10.0 m)
PE = 4900 kg x m2/s2
or 4900 Joules (J)

10. A 6 kilogram object is resting on top of a bookshelf that is 2 meters high. What is the object’s gravitational potential energy relative to the floor?
PE = mgh
PE = (6 kg) (9.8 m/s2) (2 m)
PE = kg x m2/s2
or J

11. Elastic Potential Energy
Energy of an object that has been stretched or compressed
Something is elastic if it springs back to its original shape when it is stretched or compressed
Examples: Rubber bands, strings on instruments, balls
that bounce, or springs

12. Main Forms of Energy Mechanical Energy Thermal Energy Chemical Energy
Electrical Energy
Electromagnetic Energy
Nuclear Energy

13. Mechanical Energy = Potential Energy and Kinetic Energy
Energy associated with the motion and position of everyday objects (not limited to machines)
Mechanical Energy = Potential Energy and Kinetic Energy
ME = PE + KE

14. Energy Conversion Calculations
If friction is small enough to be ignored and no mechanical energy is added to a system then….
(KE + PE) beginning = (KE + PE) end

15. 2. Thermal Energy Particles (atoms) are always in random motion
Total PE and KE related to the motion of microscopic particles makes up thermal energy
Atoms move faster - Thermal energy increases - Temperature increases
Atoms move slower - Thermal energy decreases - Temperature decreases

17. 3. Chemical Energy Energy stored in chemical bonds
When chemical bonds are broken, the energy is released
Examples: Wood, gasoline, cellular respiration of sugar, elephant toothpaste reaction

19. 4. Electrical Energy
Energy associated with electrical charges ( + and - )
Examples: Batteries or lightning bolts

20. 5. Electromagnetic Energy
Form of energy that travels through space in the form of waves
Because of their ability to travel long distances, they are often used in communication
Examples: Visible light and X-rays

22. The energy is harnessed by the fission (splitting) of atomic nuclei
6. Nuclear Energy
The energy stored in the nucleus of an atom (Due to strong and weak nuclear forces)
The energy is harnessed by the fission (splitting) of atomic nuclei
The fusion (joining) of atomic nuclei is also a form of nuclear energy

24. Energy can be converted from one form to another
The law of conservation of energy states that energy cannot be created or destroyed