1. Warm up 11/10/16 In composition book
1. How much work do you do if you lift a 9N book 1.7 meters over you head?
2. How many meters over your head do you have to lift a 5N book to do 2.5 J of work?

2. Energy

3. Energy the ability to do work or cause change
measured in units of joules (J)
Today, we will look at two general types of energy:
Potential
Kinetic

4. Potential Energy (PE) Energy that is stored in an object.
Gravitational Potential Energy – results from how high an object is above the earth.
Formula: GPE = (mass)(gravity)(height)
0.45 kg
Which soccer ball has more gravitational
potential energy? Explain your reasoning.

5. Potential energy question
The higher an object is above the earth, the more gravitational potential energy it has.

6. Which soccer ball has more kinetic energy? Explain your reasoning.
Kinetic Energy (KE)
energy of motion
depends on mass and velocity
Formula: KE = ½ (mass)(velocity)2
KE increases as mass or velocity increases and decreases as mass or velocity decreases
2 m/s
3 m/s
0.45 kg
Which soccer ball has more kinetic energy? Explain your reasoning.

7. Relationship Between PE and KE
What is happening to the PE and KE as the soccer ball falls to the feet of the mid-fielder?
PE KE
What about the PE/KE graph could be considered misleading?

8. Practice Problems
A diver weighing 46 kg is preparing for a dive from the 10 meter diving platform. How much gravitational potential energy does the diver have?
A cheetah weighing approximately 50 kg was seen chasing a gazelle at a speed of 32.4 m/s. What is the kinetic energy of the cheetah?
GPE = mgh
Earth’s
Gravity
GPE =
(46 kg)
(9.8 m/s2)
(10 m)
= 4,508 J
KE = 1mv2 2
(1)_____________ 2
(50 kg)
(32.4 m/s)2
K.E. =
= 26,244 J

9. Assignment.
Complete the energy review problems