1. What you should know about ENERGY
If it wasn't for Thomas Edison, we'd all be watching TV by the light of a candle.
MFMcGraw
Ch07 - Energy - Revised: 2/21/10

2. This lecture will help you understand:
Energy
Work
Power
Mechanical Energy : Potential and Kinetic
Conservation of Energy
MFMcGraw
Ch07 - Energy - Revised: 2/21/10

3. Ch07 - Energy - Revised: 2/21/10
What is energy?
The ability to do work.
Energy
Mover of things
Observed when it is being transferred or being transformed
Not spooky life force stuff. There is no such thing as good or bad energy, (Sorry Cesar Millan).
MFMcGraw
Ch07 - Energy - Revised: 2/21/10

4. Circular definition of work/ energy
Property of a system that enables it to do work.
Work
So, the word work, in science terms, means something transferred energy somehow.
Units for work and energy in science terms are Joules, in human terms they are Calories or kWh
MFMcGraw
Ch07 - Energy - Revised: 2/21/10

5. Ch07 - Energy - Revised: 2/21/10
Work
Work
involves force and distance.
Work = Force  distance.
whenever useful mechanical work is done:
Something changes the energy associated with that thing
MFMcGraw
Ch07 - Energy - Revised: 2/21/10

6. Ch07 - Energy - Revised: 2/21/10
But there is a catch
The force must be in the same direction as the motion
Is this dude doing any work?
What if he was dragging the bag?
MFMcGraw
Ch07 - Energy - Revised: 2/21/10

7. Ch07 - Energy - Revised: 2/21/10
But there is a catch
You might be saying, “Grist you are nuts. If I carried a heavy bag a long way I would get tired. So, I did work!”
Nope! You may have exerted effort, but you did not change the energy of the bag.
MFMcGraw
Ch07 - Energy - Revised: 2/21/10

8. Ch07 - Energy - Revised: 2/21/10
Work
CHECK YOUR NEIGHBOR
If you push against a stationary brick wall for several minutes, you might get tired, but did you do any work?
A. yes.
no.
Both of the above.
None of the above.
A. on the wall.
MFMcGraw
Ch07 - Energy - Revised: 2/21/10

9. Ch07 - Energy - Revised: 2/21/10
An Example of Work
A weightlifter raising a barbell from the floor does work on the barbell. Increasing it’s height increases its potential energy. If he dropped it on your foot it would do work on your foot.
Does he do work while holding it over his head?
Does he do work while holding it up and walking around?
Does he do work if it’s on the ground and he drags it around?
MFMcGraw
Ch07 - Energy - Revised: 2/21/10

10. Ch07 - Energy - Revised: 2/21/10
Power
Power:
Measure of how fast work is done
In equation form:
MFMcGraw
Ch07 - Energy - Revised: 2/21/10

11. Ch07 - Energy - Revised: 2/21/10
Units of Power
Unit of power
WATT is the unit of power?
Named after James Watt, developer of the steam engine
Horsepower
Named after a horse that probably carried heavy stuff or pulled things, also eater of grass and maker of manure
750 Watts = 1 horsepower
MFMcGraw
Ch07 - Energy - Revised: 2/21/10

12. Ch07 - Energy - Revised: 2/21/10
Power Examples
A worker uses more power running up the stairs than climbing the same stairs slowly. T or F
If he were to run the 2 flights of stairs would he produce more power than running just one? Yes / No
If you drove your car twice as far as usual, would your car’s engine become more powerful? Yes / No
An engine with twice the power can do twice the work of one engine in the same amount of time. T / F
MFMcGraw
Ch07 - Energy - Revised: 2/21/10

13. Ch07 - Energy - Revised: 2/21/10
Power
CHECK YOUR NEIGHBOR
A job can be done slowly or quickly. Both may require the same amount of work, but different amounts of
A. energy.
momentum.
power.
impulse.
C. power.
MFMcGraw
Ch07 - Energy - Revised: 2/21/10

14. Ch07 - Energy - Revised: 2/21/10
Mechanical Energy
Mechanical energy is due to position or to motion, or both.
There are two forms of mechanical energy:
Potential energy – position
Kinetic energy - motion
MFMcGraw
Ch07 - Energy - Revised: 2/21/10

15. Ch07 - Energy - Revised: 2/21/10
Potential Energy
Stored energy
potential for doing work
Example:
A stretched bow has stored energy that can do work on an arrow.
A stretched rubber band of a slingshot has stored energy and is capable of doing work.
MFMcGraw
Ch07 - Energy - Revised: 2/21/10

16. Potential Energy—Gravitational
Potential energy due to elevated position.
Example:
water in an elevated reservoir
Cat at the top of a tall tree
Stretched rubber band
MFMcGraw
Ch07 - Energy - Revised: 2/21/10

17. Potential Energy—Gravitational
Equal to the work done in lifting it
MFMcGraw
Ch07 - Energy - Revised: 2/21/10

18. Ch07 - Energy - Revised: 2/21/10
Kinetic Energy
Energy of motion
Depends on the mass of the object and speed squared KE = ½mv2
If object speed is doubled  kinetic energy is quadrupled.
If you double the speed you drive you quadruple you stopping distance.
(slow down!!)
MFMcGraw
Ch07 - Energy - Revised: 2/21/10

19. 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.
MFMcGraw
Ch07 - Energy - Revised: 2/21/10

20. Kinetic Energy and Momentum Compared
Kinetic energy is not momentum!!!!
Since we are not doing a unit on momentum, ask Grist or Dickson what the difference is if you are curious.
MFMcGraw
Ch07 - Energy - Revised: 2/21/10

21. Ch07 - Energy - Revised: 2/21/10
Machines
Cannot create energy, but can transfer energy
Cannot multiply (increase) total work put in or energy
MFMcGraw
Ch07 - Energy - Revised: 2/21/10

22. Ch07 - Energy - Revised: 2/21/10
Simplest Machine
Lever
Allows small force over a large distance and large force over a short distance.
MFMcGraw
Ch07 - Energy - Revised: 2/21/10

23. Ch07 - Energy - Revised: 2/21/10
Energy for Life
Body is a machine, so it needs energy.
Average people need 2000 Calories per day. = 8 million joules
This is equals 2.2 kWh about 25 cents worth of energy from LPEA
MFMcGraw
Ch07 - Energy - Revised: 2/21/10

24. Ch07 - Energy - Revised: 2/21/10
Cool energy fact
Example:
Photovoltaic cells on rooftops catch the solar energy and convert it to electricity.
More energy from the Sun hits Earth in 1 hour than all of the energy consumed by humans in an entire year!
MFMcGraw
Ch07 - Energy - Revised: 2/21/10

25. First Ever Atlas Catapult Challenge!
Teamwork
Natural resources
Requirements
Rules
By: Anne Mummery & Tom Grist

26. Teamwork
Groups of three
-General
-Engineer
-Ambassador

27. First Ever Atlas Catapult Challenge!
Teamwork
-General
Responsible for operating artillery
Strategy
Building catapult

28. First Ever Atlas Catapult Challenge!
Teamwork
-Engineer
Responsible for
Design ideas
And or research
Co-builder
Optional, video documentation

29. First Ever Atlas Catapult Challenge!←
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First Ever Atlas Catapult Challenge!
Teamwork
-Ambassador
Responsible for
Making the flag of your nation, so other nations can locate you
Learning how to welcome other teams in your native tongue
Negotiations/espionage
Battle cry

30. First Ever Atlas Catapult Challenge!
Hanger
5 marshmallows
5 army men/film canisters
Rubber bands
Spoon
Tape
Natural resources

31. First Ever Atlas Catapult Challenge!
Catapult building guidelines:
Approved materials:
Wire hanger, rubber bands, plastic spoon, and tape.
Machine requirements:
No more than 20 cm wide, 20 cm long, 20 cm tall
Approved materials only
Hanger making the frame must not bend or flex
Spoon must not flex excessively
Power must be generated by elastic potential energy from rubber band only
The flag of your sovereign nation should also have the name written on it

32. Ch07 - Energy - Revised: 2/21/10
The game set up
Please write this down!
Catapult here!
20cm
20cm
71cm
71cm
MFMcGraw
Ch07 - Energy - Revised: 2/21/10

33. Ch07 - Energy - Revised: 2/21/10
MFMcGraw
Ch07 - Energy - Revised: 2/21/10

34. Ch07 - Energy - Revised: 2/21/10
Rules!
You can…
Very nice
MFMcGraw
Ch07 - Energy - Revised: 2/21/10

35. Launch as fast as you can
Don’t call me a marshmallow, I’m a projectile!
MFMcGraw
Ch07 - Energy - Revised: 2/21/10

36. Ch07 - Energy - Revised: 2/21/10
Commit friendly fire
(FYI: this isn’t a good thing!)
MFMcGraw
Ch07 - Energy - Revised: 2/21/10

37. Any ammo on the floor is fair game!
MFMcGraw
Ch07 - Energy - Revised: 2/21/10

38. Ch07 - Energy - Revised: 2/21/10
You can’t….
MFMcGraw
Ch07 - Energy - Revised: 2/21/10

39. Ch07 - Energy - Revised: 2/21/10
Reach over the line
Only your allies or non-combatans can.
MFMcGraw
Ch07 - Energy - Revised: 2/21/10

40. Ch07 - Energy - Revised: 2/21/10
Block in-coming ammo
MFMcGraw
Ch07 - Energy - Revised: 2/21/10

41. No taping your catapult down!
MFMcGraw
Ch07 - Energy - Revised: 2/21/10

42. No lifting up your catapult!
You can move it side to side but no lifting off the table.
MFMcGraw
Ch07 - Energy - Revised: 2/21/10

43. If you break any of these rules…
You must give a live soldier to the other team
MFMcGraw
Ch07 - Energy - Revised: 2/21/10

44. Ch07 - Energy - Revised: 2/21/10
Have fun!
MFMcGraw
Ch07 - Energy - Revised: 2/21/10

45. Ch07 - Energy - Revised: 2/21/10
Have fun!
Braveheart Freedom speech
MFMcGraw
Ch07 - Energy - Revised: 2/21/10