1. Energy

2. Energy Mechanical Nonmechanical Potential Kinetic Electrical Nuclear
Chemical
Elastic
Gravitational

3. Mechanical Energy
Mechanical energy is the sum of kinetic energy and potential energy
ME = KE + PE

4. Conservation of ME MEi = MEf
With friction, this is not true because some energy is lost to heat and sound.

5. Kinetic Energy KE = energy due to motion. KE = ½ mv2
Unit= the joule (J)

6. Potential Energy
PE= stored energy
GPE= energy due to position
GPE = m· g· h

7. Elastic Potential Energy
EPE = energy in a stretched or compressed elastic object
EPE = ½ kx2

8. Spring Constant k = spring constant
Spring constant expresses how resistant a spring is to being compressed or stretched.

9. Spring Constant Flexible spring = small k Stiff Spring = large k
Spring constant = N/m

10. Work-kinetic energy theorem
The net work done on an object is equal to the change in kinetic energy of object.
Wnet = ½ mv2f – ½ mv2i
F x d = ½ mv2f – ½ mv2i

11. Practice
1. Calculate the speed of an 8000 kg airliner with KE of 1.1 x 109 J.
Knowns:
m = 8000 kg, KE = 1.1 x 109 J
Unknown: V = ?
Equation: KE = ½ mv2
1.1 x 109 J = .5(8000)v2 = m/s

12. Practice
2. A person kicks a 10kg sled, giving an initial speed of 2.2m/s. How far does it move if the force applied is 9.8 N?
Known: m = 10kg, vi = 2.2m/s, vf = 0, F = 9.8
Unknown: d = ?
Equation: F x d = ½ mv2f – ½ mv2i
9.8 x d = (10)2.22
D = 2.4 m