1. Do Now:
1. You push a crate up a ramp with a force of 10 N, but despite your pushing the crate slides 4 m down the ramp. How much work did you do?
2. A student walks up a flight of stairs that is 3 m high. If the student has a mass of 60 kg and it takes her 10 seconds to climb the stairs, then at what rate does she do work?
10N x 4m x Cos(180) = -40 J
W = 60 kg x 9.8m/s2 x 3 m

2. Aim: How does energy change?
HW: Worksheet

3. How can we describe energy conversion?
In general, the energy of position (PE)can be converted (changed) into the energy of motion (KE).
KE + PE = Mechanical E.

4. Conservation of Energy Law
Energy can not be created nor destroyed! It can only be converted into different forms!
Within a closed, isolated system (where there is no friction), total mechanical energy (KE + PE) is constant.
Equation: ME = KE + PE
Equation: Einitial = Efinal

5. The Energy was CONVERTED (CHANGED)
Another Example
Identify the kind of energy the ball has at points A, B, & C?
100 % A
Describe the difference in energy from point A to C. B
The Energy was CONVERTED (CHANGED)
100 % C

6. Pendulum Where is KE the minimum? Where is KE the maximum?
Where is PE the minimum?
Where is PE the maximum?
KE = 0
PE max
PE max
KE = 0
KE max
PE min

7. Envelope Activity
Take a look at the questions inside your envelope and take turns answer the three questions using your knowledge of energy conservation!

8. A 7 kg bowling ball falls to the floor from a height of 1. 5 meters
A 7 kg bowling ball falls to the floor from a height of 1.5 meters. What is its speed just before it hits the floor? A 3 kg object is at rest on top of a 4 meter high frictionless inclined plane. Determine Kinetic Energy at the bottom. What is Mechanical energy half way down the ramp? A 10 kilogram object strikes the ground with 2,000 joules of kinetic energy after falling freely from rest. How far above the ground was the object when it was released?

9. Do Now: Describe Mechanical Energy.
What does it mean for energy to be conserved?
How is KE related to work?
Give an example of energy being converted from one form into another.

10. A 7 kg bowling ball falls to the floor from a height of 1. 5 meters
A 7 kg bowling ball falls to the floor from a height of 1.5 meters. What is its speed just before it hits the floor?
PEmax = KEmax
103J = 0.5(7kg)v2 v = 5.4 m/s

11. A 3 kg object is at rest on top of a 4 meter high frictionless inclined plane. Determine Kinetic Energy at the bottom. What is Mechanical energy half way down the ramp?
PEmax = KEMax KEMax = 117.6J
ME = KE + PE ME = 117.6J
ME is a constant without friction

12. A 10 kilogram object strikes the ground with 2,000 joules of kinetic energy after falling freely from rest. How far above the ground was the object when it was released?
PE = mgh
2000J = (10kg)(9.8m/s2)h
h = 20.4m

13. Station Activity
Work with your partners at the following stations.

14. Station 1
A basketball with mass 0.62 kg is shot in the air. If there is 22 J of work done to shoot the ball to some height, then how much potential energy is gained? How high does the ball go? Justify

15. Station 2
A 10g pendulum swings back and forth. The height at point 1 is 5 cm and the height at point 4 is 2.5 cm.
What is the system’s ME?
What is the KE at 3?
What is KE at 4?

16. Station 3 True or false As a car drives up a ramp it gains ME.
As a car slows down the work done is positive.
A pendulum has maximum PE at the highest point in it’s motion.
A roller coaster can have it’s second hill be higher than the first.
PE is zero only on the ground.
ΔKE = Power - Work

17. Summary
Describe how energy is conserved as a ball is thrown up and down.
What is the total energy in terms of KE and PE?
An arrow is shot up in the air. Where is max KE and PE? How is energy conserved for the arrow?

18. Energy Skate Park
Lets play around with different situations and examine the energy involved!

19. Activity I - A closer look at a pendulum
Where is KE max?
Where is PE max?
Explain how energy is conserved.
How does ME half way down compare to ME at bottom? Explain.