1. Energy and Work And you

2. Energy KE, gPE, TE, EPE … Units: Newton meter = kg (m/s 2 ) (m) = kg m 2 /s 2 = Joule

3. Notice that: The Newton is a unit of Force The meter is a unit of displacement

4. Work = Force applied parallel to the displacement of an object. If I carry books across the floor, I apply a force up (against the F of gravity) and I move horizontally across the floor. Therefore, I do no work on the books Because my force is not parallel to the displacement!

5. Work Example: Watch as I push a cart with a force of 10 N across the floor for 10 meters What would a force –vs- displacement graph of this situation look like?

6. Like this 10 F (N) 0 displacement (m) 10 What does the area under the curve represent?

7. If you said: The work done – then you are one smart cookie!!!! Notice area = height x length = N x m = Nm = Joules!

8. But wait just one minute mister! I thought you said that the units of energy were the Joules That is correct I did! Look at these next few examples please

9. Potential E/work equivalence If you are on top of a diving board gPE = mg h W = F d F = mg and h = d therefore: W = mg h

10. How sick is that???? Way sick!!!!

11. What about KE????

12. This work/energy equivalence Allows us to do some cool calculations! Like this…

13. E pbm. #1 If you are on a roller coaster that is 40 m high, what is your velocity at the bottom of the ride (ignore E loss to TE) E top = E bottom gPE = KE mgh = ½ mv 2 therefore: V = mgh/ 1/2 m = 2gh = 28 m/s

14. E pbm #2 What would your velocity be 20 from the top? gPE 40m = gPE 20m + KE mg(40) = mg(20) + 1/2mv 2 m(9.8)(40) = m(9.8)(20) + ½ mv 2 392 = 196 + ½ v 2 (392 – 196)(2) = v 2 V = 19.8 m/s

15. Pbm. #3 A 200g baseball is hit straight up with an initial velocity of 20 m/s. How high will it go? KE = gPE ½ mv 2 = mgh h = ½ v 2 / g (* just like earlier in the year) h = 20.4 m high

16. Pbm #4 If the ball only goes 19.5 m high (instead of the calculated 20.4 m) then what is the force of friction acting on the ball? TE = F fr ΔX KE = gPE + TE TE = KE - gPE F fr = KE - gPE / ΔX F fr = ~.09N

17. And Now A short discussion on NUCLEAR Power