1. Potential Energy and Kinetic Energy Day 2
Mechanical Energy:
Potential Energy and
Kinetic Energy
Day 2

2. Curriculum
Big Idea: Energy can be transferred between objects and/or can be converted into different forms.
Concept: Energy is conserved (Law of conservation of energy).
PA Standard 3.2.C.B3: Describe the law of conservation of energy.

3. Goals Students should be able to:
State the Law of Conservation of Energy
Define potential energy
Define kinetic energy
Discuss the factors that determine the relative amounts of kinetic and potential energy in an object
Give examples of objects that have PE and KE.

4. Today’s Agenda – 10/28/10 Opener: What is energy?
Test of Courage: The Pendulum (see energy packet and powerpoint)
Challenge: Pendulum online lab simulation
Answer Concept Questions: in the powerpoint
Problem Solving: Pendulums and Rollercoasters
(in packet)
Closure: Re-answer the “What Do You Think?” Questions (on a note card).
Take Home Assignment: #6 - #10 on page 119 in Conceptual Physics

5. Review: A ball was dropped off a cliff.
What happened to the PE?
The PE decreased as the ball’s height decreased.
What happened to the KE?
The KE increased as the ball’s velocity increased.
What happened to the PE + KE?
The PE + KE stayed the same

6. Concept Question
When the pendulum swings back and forth, do you think that the total energy (PE + KE) increases, decreases, or stays the same?
a. The total energy increases
b. The total energy decreases
c. The total energy stays the same

7. If there were no outside forces on the pendulum, the total energy of the pendulum would stay the same (conservation of energy).
The PE + KE of the pendulum actually decreases. We can tell that its energy decreases because the pendulum slows down and eventually stops moving. Energy is still conserved. Go on to the next concept question…

8. Concept Question
In terms of energy, why will you never get hit by the pendulum (as long as you don’t give it a push)?
a. Energy transfers from the pendulum to the air in the form of heat.
b. Energy in the pendulum disappears.
c. The pendulum continuously gains energy from its surroundings.
d. The pendulum always reaches its initial height, even WITH friction and air resistance!

9. Energy is conserved
The pendulum system loses energy.
The energy did not disappear.
Energy is always conserved.
In this case, some energy is transformed into heat due to air resistance. Heat is another form of energy. The pendulum heats up the air!

10. Challenge: Pendulum Online Lab Simulation
As a class, change the air resistance for the pendulum in the following online lab simulation using the interactive white board in the front of the class, and see if you can match up the frequency of our pendulum in class to the pendulum online so that we can theoretically find the air resistance on our pendulum:

11. Pendulum Problem

12. Pendulum Problem

13. How does gravity affect PE?

14. How does gravity affect PE?

15. Roller Coaster Problem

16. Key Terms
energy: the property of an object or a system that enables it to do work; measured in joules.
kinetic energy: energy of motion, equal to half the mass multiplied by the speed squared.

17. Key Terms
potential energy: energy of position, usually related to the relative position of two things, such as a stone and Earth, or an electron and a nucleus.
Law of Conservation of Energy: Energy cannot be created or destroyed. It may be transformed from one form into another, but the total amount of energy never changes.

18. Closure
Re-answer the “What Do You Think?” Questions on a note card