1. “EnergyTransformations”
Ch. 13
“EnergyTransformations”

2. Energy Energy is a measure of the ability to do work.
SI Unit for energy: Joule (J)
There are two main categories of energy, nonmechanical and mechanical energy.

3. Nonmechanical Energy
Nonmechanical energy is small scale (meaning the scale of atoms).
Examples of NME include: thermal/heat, electromagnetic, nuclear, electric, sound, and chemical.

4. Nonmechanical energy Chemical Energy:
Energy associated with both the making and breaking of chemical bonds.

5. Nonmechanical energy Nuclear Energy:
Energy that binds the nucleus of an atom together. Can be released through nuclear fission or fusion.

6. Nonmechanical energy Electromagnetic Energy:
Form of energy made from electrical and magnetic waves and packets of energy called photons.

7. Nonmechanical energy Sound Energy:
Energy that travels in waves by vibrating molecules in a medium.

8. Nonmechanical energy Electrical Energy:
Energy associated with the flow of electrons through wires or other conducting materials.

9. Nonmechanical energy Thermal/Heat Energy:
Energy associated with the average kinetic energy of atoms or molecules.
Heat energy can be transferred in three ways:
Conduction
Convection
Radiation

10. Potential Kinetic Mechanical Energy
Mechanical energy is composed of 2 types: GPE (gravitational potential energy) and KE (kinetic energy). ME is large scale meaning you can SEE it.
Potential
Kinetic

11. Potential Energy
Potential Energy is the stored energy resulting from the relative positions of objects in a system.
There are two types:

12. Potential Energy
Elastic Potential Energy

13. Potential Energy
Gravitational Potential Energy

14. GPE (J) = mass (kg) x free-fall acceleration (9.8 m/s2) x height (m)
Potential Energy
GPE (J) = mass (kg) x free-fall acceleration (9.8 m/s2) x height (m)
GPE = mgh
g = 9.8 m/s2
GPE
(m x g x h)

15. Kinetic Energy
Kinetic Energy is the energy of a moving object due to its motion.

16. Kinetic Energy (J) = ½ x mass (kg) x speed2 ([m/s]2)
KE = 1/2mv2 KE
(.5 x m x v2)

17. KE’s equation shows us that two main things affect KE:
Kinetic Energy
KE’s equation shows us that two main things affect KE:
Mass
Speed

18. Kinetic Energy Mass: As an objects mass increases, so does its KE.
I have a BIG kinetic energy when I’m moving!
I have a SMALL kinetic energy when I’m moving!

19. Penny off of the Empire State Building
Kinetic Energy
Speed: As an object’s speed increases, so does its KE. So as any object falls, its KE increases.
Penny off of the Empire State Building

20. Potential Energy
Calculate the gravitational potential energy of a 1200 kg car at the top of a hill that is 42 m high.
GPE = ?
m =
1200 kg
g =
9.8 m/s2
h =
42 m
GPE = m x g x h
GPE = 1200 x 9.8 x 42
GPE = 493,920 J
GPE
(m x g x h)

21. Potential Energy
If a penny is sitting at the edge of a building with a mass of kg and a gravitational potential energy of 0.147, How tall is the building?
GPE =
0.147 J
m =
0.0005
g =
9.8 m/s2
h = ?
h = GPE / (m x g)
h = / ( x 9.8)
h = / (0.0049)
h = 30 m
GPE
(m x g x h)

22. Kinetic Energy
What is the kinetic energy of a 44 kg cheetah running at 31 m/s?
KE = ?
m =
44 kg
v =
31 m/s
v2 =
961 (m/s)2
KE = .5 x m x v2
KE = (.5)(44)(961)
KE = 21,142 J KE
(.5 x m x v2)

23. Kinetic Energy
A bowling ball traveling 2.0 m/s has 16 J of kinetic energy. What is the mass of the bowling ball in kilograms?
m = ?
KE =
16 J
v =
2 m/s
v2 =
4 (m/s)2
m = KE / (.5 x v2)
m = 16 / (.5 x 4)
m = 16 / (2)
m = 8 kg KE
(.5 x m x v2)

24. Kinetic Energy
A 35 kg child has 190 J of kinetic energy after he sleds down a hill. What is the child’s speed at the bottom of the hill?
v = ?
v2 = ?
KE =
190 J
m =
35 kg
v2 = KE / (.5 x m)
v2 = 190 / (.5 x 35)
v2 = 190 / (17.5)
v2 =
v = 3.3 m/s KE
(.5 x m x v2) √

25. Law of Conservation of Energy
The Law of Conservation of Energy says that energy cannot be created or destroyed, it can only change forms.

26. Law of Conservation of Energy
A perpetual motion machine is a machine designed to keep going forever without any input of energy.
This means ALL of the energy put into the machine stays in the machine perpetually (forever).
It’s a perfect model of the law of conservation except it’s
IMPOSSIBLE!!!!
Energy is constantly Changing forms!
Taccola’s Wheel

27. Law of Conservation of Energy
Potential energy can be transformed into kinetic energy and vice versa.
Example:
As a roller coaster is pulled up to the top of the first hill, the mechanical energy is stored as gravitational potential energy.
As it goes down the other side of the hill, the roller coaster picks up speed, transforming the potential energy to kinetic energy.
Roller Coaster Physics Design Your Own Roller Coaster