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# Physics chapter 10 and 11

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Ch 10,11 Notes

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### Physics chapter 10 and 11

1. 1. Chapter 10 Work, Power & Simple Machines
2. 2. Work <ul><li>Work – product of force exerted on an object and the distance the object moves in the direction of the force. </li></ul><ul><li>W = F (d) Units: N*m = 1 Joule </li></ul><ul><li>W = F (d) cos θ </li></ul>
3. 3. Power <ul><li>Power – the rate of doing work; rate at which energy is transferred </li></ul><ul><li>P = W / t Units: J/s = 1 Watt </li></ul>
4. 4. Machines <ul><li>Machines – </li></ul><ul><li>ease the load by changing the magnitude or direction of a force, but it does not change the work done. </li></ul>
5. 5. 2 Parts of the Machine <ul><li>Effort Force (F e ) - force exerted by you </li></ul><ul><li>Resistance Force (F r ) - Force exerted by the machine </li></ul><ul><li>W in = F e (d e ) </li></ul><ul><li>W out = F r (d r ) </li></ul>
6. 6. Mechanical Advantage vs. Ideal Mechanical Advantage <ul><li>Mechanical Advantage (MA) is the ratio of resistance force to effort force </li></ul><ul><li>MA = F r / F e </li></ul><ul><li>Ideal Mechanical Advantage (IMA) </li></ul><ul><li>assumes transfer of all energy (No friction) </li></ul><ul><li>IMA = d e / d r </li></ul>
7. 7. Efficiency of a Machine <ul><li>Efficiency of a machine is the ratio of output work to input work. </li></ul><ul><li>Efficiency = (W out / W in ) x 100 </li></ul><ul><li>Efficiency = (MA / IMA) x 100 </li></ul>
8. 8. 6 Simple Machines <ul><li>Lever </li></ul><ul><li>Pulley </li></ul><ul><li>Wheel and Axle </li></ul>
9. 9. Simple machines in the inclined plane family <ul><li>Inclined Plane </li></ul><ul><li>Wedge </li></ul><ul><li>Screw </li></ul>
10. 10. 1 st Class Lever <ul><li>The pivot is between the effort and the resistance (load) </li></ul><ul><li>Ex: Catapult, See-saw </li></ul>
11. 11. 2 nd Class Lever <ul><li>Pivot is on one end and resistance force is in the middle </li></ul><ul><li>Ex: Wheelbarrow </li></ul>
12. 12. 3 rd Class Lever <ul><li>Pivot is on one end and effort force is in the middle </li></ul><ul><li>Ex: Broom, Hockey Stick, Shovel </li></ul>Load Effort Pivot
13. 13. Chapter 11 Potential and Kinetic Energy
14. 14. Energy <ul><li>Energy – the ability to change an object or its surroundings </li></ul><ul><li>There are several types of energy, but we will focus on these two. </li></ul><ul><li>Potential Energy – energy stored in an object because of its position or state </li></ul><ul><li>PE = mgh </li></ul><ul><li>Kinetic Energy – energy due to the motion of an object </li></ul><ul><li>KE = 1/2mv 2 </li></ul>
15. 15. Work Energy Theorem <ul><li>The net work done on an object is equal to its change in kinetic energy. </li></ul><ul><li>Work = ∆KE = KE f – KE i </li></ul><ul><li>If the net work is positive (Force is in the same direction as motion) then KE increases; if the net work is negative (Force in the opposite direction as motion) then KE decreases. </li></ul><ul><li>F d = KE f – KE i </li></ul>
16. 16. The Law of Conservation of Energy <ul><li>Within a closed, isolated system energy can change form, but the total amount of energy is constant. </li></ul><ul><li>KE i + PE i = KE f + PE f </li></ul><ul><li>Mechanical Energy = KE + PE </li></ul>
17. 17. Energy of a Pendulum <ul><li>Where is the potential energy the greatest? </li></ul><ul><li>1 and 5 </li></ul><ul><li>Where is the kinetic energy the greatest? </li></ul><ul><li>3 </li></ul><ul><li>If the pendulum has 10 J of kinetic energy at point 3, how much mechanical energy does it have at point 4? </li></ul><ul><li>10 J </li></ul>
18. 18. Why is the first hill the highest on a roller coaster? <ul><li>It has to store the most potential energy so it can be converted to kinetic energy to finish the ride. </li></ul>
19. 19. The energy conversions in the pole vault <ul><li>Kinetic on the runway </li></ul><ul><li>Elastic when the pole bends </li></ul><ul><li>Potential and Kinetic as he moves off the ground </li></ul><ul><li>All potential at bar clearance </li></ul><ul><li>Kinetic as he hits the mat </li></ul><ul><li>Thermal after the landing </li></ul>
20. 20. Elastic and Inelastic Collisions <ul><li>Perfectly Elastic Collision (Bounces) – A collision where the kinetic energy is conserved </li></ul><ul><li>Inelastic Collision (Sticks) – A collision where some of the kinetic energy is changed into other forms (usually heat) </li></ul>