3. The unit to measure work is ___________ The two requirements: 1. 2. Example: How much work is done if the guy pushes with 40 N to move the 20 N box 4 m? FORCE DISTANCE Something must move Force must be in same direction as movement Joules

4. The unit to measure work is ___________ The two requirements: 1. 2. Example: How much work is done if the guy pushes with 40 N to move the 20 N box 4 m? FORCE DISTANCE Something must move Force must be in same direction as movement Joules

5. The unit to measure power is _________________ Example: What is the power needed to raise a 30 N object 3 m in 4 sec? work time Watts

6. ________________ - Energy of motion KINETIC ENERGY KE = ½ mv 2 Kinetic energy (Joules) Mass (kilograms) Velocity (m/s)

7. ________________ - Stored energy GRAVITATIONALELASTICCHEMICAL POTENTIAL ENERGY PE grav = mgh mass9.8height PE spring = ½ kx 2 spring constant elongation

8. TOTAL ENERGY IS CONSERVED Changes from one form to another……….. KINETIC ENERGY POTENTIAL ENERGY WORK HEAT SOUND ALL ENERGY CAN BE ACCOUNTED FOR All measured in JOULES What are the FUNDAMENTAL UNITS that make up a JOULE?

9. 3 m v? A B NO FRICTION Energy is conserved ………… E A = E B PE grav =KE mgh= ½ mv 2 (9.8)(3) =½ v 2 v = 7.67 m/s

10. 3 m v? A B NO FRICTION Energy is conserved ………… E A = E B PE grav =KE + PE grav mgh A = ½ mv 2 + mgh B (9.8)(3) =½ v 2 + (9.8)(1.4) v = 5.61 m/s 1.4 m

11. 3 m A B NO FRICTION ????? Ball CAN’T roll higher than 3 m ….…unless you add more energy

12. NO EDo WorkPE elastic KEKE + PE PE grav KE + PE NO E What happened to the ENERGY?!?

13. Energy is the SAME at all positions unless……. turns into sound or heat lost to work against friction. - Energy is ADDED- Energy is DISSIPATED Something does work ON it Not really LOST

14. 8 m/s? m/s 2m  =.200 E A - E friction = E B v = 7.49 m/s ½ mv 2 - F f d = ½ mv 2 ½ m(8) 2 - (.200)(9.8m)(2) = ½ mv 2

15. Compressed 8cm k = 480 N/m 3 kg ? E A = E B PE spring = PE grav ½ k x 2 = mgh ½ 480 (.08) 2 = (3)(9.8)h