1. **Bring up your Work and Power Lab to hand in for credit!**
April 26, 2010
What is the difference between potential and kinetic energy?
What are the units for energy?
**Bring up your Work and Power Lab to hand in for credit!**

2. Goals To explain different types of energy
To calculate potential and kinetic energy
Eureka Kinetic Energy
Eureka Potential Energy

3. Q: What is ENERGY? Work and energy are INTERCHANGABLE Energy is….
the ability to do work
a measure of how much work is done
a word to describe the power and effort of a force.
measured in Joules

4. ENERGY Energy is the ability to do work Doing work uses energy
An object can gain energy if work is done on it

5. Q: What is ENERGY? Two MAIN states of energy: Potential energy
Kinetic Energy

6. Q: What is POTENTIAL ENERGY?
Potential Energy (PE) is stored energy
Coaster has PE when it is at the top of the hill. Even if it isn’t moving yet, it may if a force is applied and it begins to move

7. Q: What is POTENTIAL ENERGY?
Gravitational potential energy (GPE) is the energy of an object due to its position above the surface
GPE = mgh = wh
m=mass (in Kg)
g=acceleration due to gravity … 9.8 m/s2
h= height (in m)
w = weight (N)  add this in your notes
UNITS: kg x (m/s2) x m = N-m = Joule (J)

8. “Homework” Complete the Practice Problem for PE on your note sheet!
Add the triangles to your notes!
If you are given mass (kg), use this triangle.
If you are given weight (N), use this triangle. PE PE g h h m w

9. Equation: GPE = m x g x h h = 35 m m = 65 kg g = 9.8 m/s2 GPE = ?
PRACTICE PROBLEM: Find the PE of a rock climber as she climbs 35 m above the base of a cliff. Her mass is 65 kg.
Equation:
GPE = m x g x h
Given:
h = 35 m
m = 65 kg
g = 9.8 m/s2
GPE = ?
Solve: GPE =
65 kg x 9.8 m/s2 x 35m
=22,295 J

10. Potential Energy (add this to your notes)
PE is directly proportional to mass, weight, and height
EXAMPLE: If any one of those quadruples, PE will do the same

11. Q: What is KINETIC ENERGY?
Kinetic Energy (KE) is the energy due to an object’s motion
Active energy
A rock as it falls off of a cliff
Formula: KE = ½ * m * v2
m= mass (kg)
v = velocity (m/s)
UNITS: kg X (m/s)2 = Joule (J)

12. Kinetic Energy Equations (Put these in your notes!)
KE = ½ * m * v2
V = √ (2KE/m)
m = 2KE/v2

13. PRACTICE PROBLEM: What is the KE of a 44 kg Cheetah running at 31 m/s?
Given:
m = 44 kg
v = 31 m/s
KE = ?
Equation:
KE = ½ * m * v2
Solve: KE =
(1/2) (44 kg) (31 m/s)2
21,142 J

14. Kinetic Energy (add this to your notes!)
Kinetic energy is directly proportional to mass
EXAMPLE: If mass triples, KE will triple
Kinetic energy is directly proportional to velocity SQUARED!
EXAMPLE: If velocity triples, KE will be multiplied by 9 (32 = 9)

15. Homework Part 2 and 3 of homework packet- due tomorrow!
Remember: Energy is the same thing as work (a measure of work done!)