2. Work (Pay special attention to words in BLACK) What is “Work”? According to physics… Work is a force applied for a certain distance. W=F  x

3. Work A 50 Kg car is moved 40 m by a 30 N force. How much work is done to the car? 1200 Nm 1Nm = 1 Joule = 1 J So, W = 1200 J

4. W = F  x = ma  x But, V f 2 =V i 2 +2a  x Rearrange: a  x= (V f 2 -V i 2 )/2 Substitute: W= ma  x = m (V f 2 -V i 2 )/2 So: W = 1/2m V f 2 -1/2mV i 2 1/2mv 2 has a special name: Kinetic Energy!

5. Kinetic Energy Kinetic energy is another way that physics looks at motion: KE = 1/2mv 2 Looking back… W=  KE So: Work is the change in Kinetic Energy.

6. Kinetic Energy Reconsidering the car problem: If the 50 Kg car began at rest and experienced 1200 J of work how fast is the car traveling after the work is done? V f =6.9 m/s

7. Potential Energy Potential energy is anything that has the potential to do work to an object. A rock on top of a hill, a stretched slingshot, a hydrogen/Oxygen mixture etc. (What types of potential energy are each of the examples?)

8. Gravitational Potential Energy: PEg = mgh m = mass, g = 9.8 m/s 2, h = height

9. Gravitational Sample A 2000 Kg boulder sits 43m above the ground on top another larger boulder. What is the potential energy of the top boulder? PEg = 842,800 J

10. Elastic Potential Energy PEe= 1/2kx 2 k = spring constant = F/x (Hooke’s Law) X= displacement from the relaxed position F = Force

11. A 45 Kg block is against a spring with spring constant 950 N/m. The spring is compressed 10 cm from the relaxed position. How much energy is stored in the spring? PEe = 4.8 J

12. Conservation of Energy Energy cannot be created nor destroyed. The total mechanical energy initially must equal the total mechanical energy finally.  MEi =  MEf KE i +PEg i + PEe i = KE f + PEg f + PEe f

13. Conservation of Energy KE i +PEg i + PEe i = KE f + PEg f + PEe f KE is the Energy of “MOVING” PEg is the energy of “UP” PEe is the energy in a “SPRING” Moving?Up?Spring? Moving?Up?

14. A 2000 Kg boulder sits 43m above the ground on top another larger boulder. It falls! How fast is the boulder moving just before hitting the ground? V f = 29 m/s

15. A spring with a spring constant of 35 N/m is compressed 0.23 m from its relaxed position. Resting against this spring is a 0.08 Kg character. When the character is released, what is his maximum velocity? 4.8 m/s

16. Pendulum A pendulum has a 5.0 Kg mass attached to a 1.2 m long string. If the pendulum is brought back through an angle of 25 o, what will the maximum velocity be? 1.4 m/s