1. WORK, ENERGY, AND POWER

2. WORK ENERGY required to move an object a certain distance W = F · d Where: W = work (joules or kilojoules) F = force (N) d = displacement (m)

3. WORK Two Rules: Objects must have a force applied (accelerate) Objects must be displaced (use +/- signs) Ex: Mr. F pushes against the wall for an hour without the wall moving and then gives up…work done on the wall? Ex: A book falls from a desk and freefalls to the ground…work done on the book? (+/- ?)

4. WORK Example: A pro-wrestler lifts an opponent 1 meter over his head with 2000N of force. How much work did the wrestler do?

5. WORK Example: A pro-wrestler lifts an opponent 1 meter over his head with 2000N of force. How much work did the wrestler do? He lowers the opponent instead of throwing them…how much work did the wrestler do?

6. KINETIC ENERGY (K) When an object is moving it has kinetic energy K = 1/2mv 2 Where: K = Kinetic energy (J or kJ) m = mass (kg) v = velocity (m/s)

7. KINETIC ENERGY (K) Example: A roller coaster cart with a mass of 250kg reaches a speed of 19.5 m/s at the bottom of a hill. How much kinetic energy does the cart have?

8. WORK & KINETIC ENERGY (K) Since work is done when something is accelerated (changes velocity) we can relate K and W. W = K final – K initial

9. WORK & KINETIC ENERGY (K) Example: The rollercoaster cart with a mass of 250kg slowed from 19.5m/s to 5 m/s going up a hill. How much work did the cart do to climb the hill?

10. BEFORE WE PRACTICE Main ideas: - Both W and K use Joules and kiloJoules - Work requires displacement - Kinetic energy requires movement (velocity) - The difference in K is equal to W

11. WORK MINI LAB There are 7 different objects placed around the room: 1) Mass the object on a scale 2) Multiply by 9.8 m/s 2 to get force 3) Lift the mass a total of 1 meter high 4) Calculate the work done to lift the mass On a separate sheet of paper make a data table: Object Mass (kg)Force (N) Distance (m)Work (J)

12. WORK Let’s say you have to move a couch into a U-Haul truck…is it easier to lift it vertically into the truck or to use the ramp? Which requires less work?Which requires less work

13. WORK Squat vs. Leg Press – which is easier?

14. REVIEW FROM YESTERDAY - No distance moved = no work done - Speeding up and slowing down require work - Kinetic energy not the same as velocity W = FdK = 1/2mv 2 W = K f – K i a.k.aW = (1/2mv f 2 ) – (1/2mv i 2 )

15. EXAMPLE: A gun exerts a 15,000N force on a 0.1kg bullet over a distance of 0.25 m. Assuming the bullet starts from rest, what is the final velocity of the bullet?

16. MINI LAB - Measure the mass of the dune buggy - Measure the velocity of the buggy with a meter stick and stopwatch - Use K = 1/2mv 2 to calculate the kinetic energy of the buggy. - Record this data and show all work on a separate sheet of paper and hand in 1/group