1. Warm-up! - use your notes from yesterday
How much work is done on a 100-N boulder when you lift it 2m?
What power is expended if you lift the same boulder a distance of 4.5 meters in a time of 2.5 seconds?
Be sure to diagram the problem, separate the variables, identify the necessary equation, plug in the variables, calculate and solve. Include all SI units.
December 11, 2012

2. Answers: W = Fd W = (100-N)(2m) = 200 joules ~~~~ power = work / time
(100-N)(4.5m) / (2.5 s) = 180 watts

3. in 1 second requires one watt of power?
Did you know that to vertically lift a quarter- pound hamburger with cheese 1 meter
in 1 second requires one watt of power?

4. Reminders:
If you need to make up the test from last Friday, schedule a time with Mr. Kipp ASAP!
You will only have one week (this week) to make up the test.

5. Today's plan: We have a pretty laid back day...
We will continue introducing some of the concepts from Chapter 8.
You will have time at the end of class to complete the homework.

6. Energy lecture continued...
What is energy?
Make a heading in your notes
entitled "types of energy" and brainstorm
at least 6 different types of energy.

7. Mechanical Energy
The two forms of mechanical energy are kinetic energy and potential energy.
The property of an object or system that enables it to do work is energy.
Like work, energy is measured in joules.
Mechanical energy is the energy due to position of something or the movement of something.

8. Potential Energy
Three examples of potential energy are elastic potential energy, chemical energy, and gravitational potential energy.
Energy that is stored and held in readiness is called potential energy (PE) because in the stored state it has the potential for doing work.

9. Elastic Potential Energy
some examples:
a stretched or compressed spring
a bow that is drawn back
and a stretched rubber band

10. Chemical Energy
The chemical energy in fuels is potential energy at the submicroscopic level.
This energy is available when a chemical change in the fuels takes place.
some examples:
food, gasoline, coal, firewood, etc.

11. Gravitational Potential Energy:
Gravitational potential energy is the potential energy due to the elevated position of an object.

12. How to measure GPE
The amount of gravitational potential energy possessed by an elevated object is equal to the work done against gravity in lifting it.
Gravitational potential energy = weight x height
In equation form: PE = mgh
The height in this equation is the distance above some chosen reference level.

13. Think of it this way...
If you were to drop a bowling ball on your toe, first from a distance of 1 mm above your toe and then from distances up to 1m above your toe...
Each time, the bowling ball would do more work on your toe because it would possess more gravitational PE when released.

14. Using the equation for calculating gravitational potential energy,
Calculate the gravitational potential energy given to a 100-kg boulder that is lifted a height of
2 meters.
remember,
PE = mgh
NOTE: don't confuse kilograms with Newtons here!

15. Answer:
1960 joules
because,
1960 J = (100-kg)(9.8m/s)(2m)

16. Homework -
You have class time to complete the handout from yesterday and turn in at teacher's desk before you leave.
Today's assignment:
Page 119, #s 1-7 in your text
Write the questions and the answers on a separate sheet of paper and turn in at the teacher's desk.
Be sure to show all calculations with SI units.