1. Energy

2. 1. What is Energy? “Something” that enables an object to do work.
When you have “Energy” you can do work
A. The amount of energy that an object has is related to the amount of work the object can do.
The amount of energy can be precisely measured
B. SI unit is Joules (for energy
and work)
Comes in various forms

3. 2. How do we get energy to do work??
By eating
A. When you are sick and not feeling well, do you have a lot of energy to go shopping or play basketball? No
B. Why?
Because we are not eating.

4. 3. What are the 2 main forces of Energy?
A. Potential
1. Stored Energy
A. Has stored ability to move matter
Kinetic
1. Energy of Motion

6. 4. Types of Potential Energy
1. Gravitational
2. Elastic
3. Chemical
4. Nuclear
5. Magnetic
6. Electrostatic

7. 5. What is Gravitational Potential Energy?
Energy due to gravity acting on an object
PE = mgh
m = mass in kg
g = acceleration due to gravity (m/s2)
h = height in meters
Gravity = force of attraction between any 2 objects)

8. 6. What is Elastic Potential Energy?
Elasticity
A. When stretching a rubber band
The potential energy is the energy that powers the rapid return to shorter original length.
B. Ball bouncing
Round shape flattens as hits ground – alters tension
Then returns to round shape and allows it to bounce

9. 7. What is chemical potential energy?
Energy stored within the bonds of a substance.
Uses Conservation of Mass – total amount of matter does not change
Example:
A. eat cheeseburger
Gives energy to run
B. gas in a car allows it to move.

10. 8. What is nuclear potential energy?
Energy stored in the bonds of subatomic particles
Either split (fission)or fuse (fusion) of atoms
Some mass is transformed into energy.

11. 9. What is magnetic potential energy?
Attraction or repulsion from magnetic energy stored in objects
CME’s – coronal mass emissions from sun’s magnetic field
Magnets – anything with iron in it

12. 10. What is electrostatic potential energy?
Attraction or repulsion of electrical charges
Example: clean sock sticking to clothes after it comes out of a dryer
Hair standing on
end

13. 11. Types of Kinetic Energy
1. Mechanical
2. Thermal
3. Electrical
4. Nuclear
5. Sound
6. Electromagnetic
KE = 1/2mv2
M = mass in kilograms
V = velocity (m/s)

14. 12. Mechanical Vs Non-Mechanical Energy
Energy that an object has due to its motion or position
Mass is, or will be, displaced (moved)
Kinetic or Potential
Non-Mechanical
Mass is not displaced, no movement or velocity gained or lost
Examples
Heat energy (fire)
Chemical Energy
Gasoline
Food

15. 13. What is thermal energy?
Total energy in a substance measured in units of heat or temperature.
Examples:
A. Ice melting
B. Water boiling
C. Warm water in a shower
D. Frying an egg

16. 14. What is electrical energy?
Energy associated with movement of charges
Examples:
A lit light bulb
Ex. Lightning – electricity
Positive and negative charges collect in different parts of clouds
When there are a lot of charges – get lightning
Electricity travels between areas of opposite charges

17. 15. What is sound energy?
Energy transmitted through compression of matter
Examples:
A. Hearing music
B. Hearing thunder

18. 16. What is electromagnetic energy?
Energy that travels in waves and can travel in a vacuum
A. Visible light
B. Rainbow
C. Radio waves

19. Sample Problem #1
6 kg
What is the potential energy of a 6kg bowling ball at a height of 20 meters?
Gravitational Potential energy is
PE = (mass) x (Gravity) x ( Height )
= (6 kg)x (9.8 m/s2 ) x ( 20 m )
= 1176 Joules
What is potential energy at the bottom (zero height)?
At a height of zero meters PE is zero Joules.
20 m

20. Kinetic Energy (KE) A stationary object has zero kinetic energy
Energy associated with an object due to its motion.
If something is in motion it has the ability to do work
A stationary object has zero kinetic energy
KE = ½mv2
KE= ½ x Mass x Speed2
Notice that speed is squared, so a small increase in speed will result in a larger increase in KE!

21. Sample Problem #2
6 kg
What is the kinetic energy of a 6kg bowling ball, falling from a height of 20 meters just as it reaches the ground with a speed of 19.8 m/s?
Kinetic energy is
(Kinetic Energy) = ½ ( Mass ) x ( Speed ) = ½ x( 6 kg ) x ( 19.8 m/s )2
= Joules
20 m
20 m/s

22. 17. Conservation of Energy
Law of Conservation of Energy states that energy can never be created or destroyed. It can only be transformed from one form into another.
Example
A book falls from a table
A rubber band pulled back
The total Mechanical Energy must always be equal to the sum of Kinetic Energy and Potential Energy
Etotal = KE + PE

23. Can predict speed from height
Pendulum
“Like a child on a swing”
Energy exchange from PE to KE and back.
Maximum
Height
Maximum
Speed
Maximum
Height, again
Check it out!
Can predict speed from height
since PE+KE constant

24. More than Meets the Eye
Watch below as the KE and the PE change as the car changes height and speed. Notice that no matter when you look at the two bars, there is only the same amount of energy that you started with.
Watch This!

25. 18. Check for Knowledge
Suppose you have a 1 kg mass at a height of 1.25 m. How much potential energy does it have?
The mass is now let go. At the very bottom, what is it’s kinetic energy?
What is the speed of the mass just before it hits the ground?