1. Chapter 8 Energy

2. Work = force x distance W = Fd - application of a force - movement of something by that force

3. Work is measured in Joules Joule (J) = N*m

4. Power – the rate at which work is done measured in watts

5. Power = work done time interval

6. Mechanical Energy Definition: the energy due to the position of something or the movement of something

7. Potential Energy (PE) Definition: energy that is stored and held in readiness Examples: stretched rubber band, fossil fuels, food

8. Gravitational PE PE due to elevated positions GPE = weight X height PE = mgh

9. Kinetic Energy (KE) Definition: energy of motion Examples: throwing a ball, moving car

10. KE = 1/2mv 2

11. Work-Energy Theorem: Work =  E

12. Law of Conservation of Energy Energy cannot be created or destroyed. It can be transformed from one form into another, but the total amount of energy never changes.

13. Machines definition: device used to multiply forces or simply to change the direction of forces

14. Input force: the force you exert on the machine Output force: the force exerted by the machine

15. Types of Simple Machines (there are 6 of them)

16. 1. Lever 2. Wheel and Axle 3. Pulley 4. Inclined Plane 5. Screw 6. Wedge

17. lever - a bar that turns about a fixed point; Ex. crowbar

18. Fulcrum: the fixed point on which a lever turns or pivots fulcrum

19. The lever exerts a large force over a short distance while you exert a small force over a long distance

20. TYPES OF LEVERS: - refer to drawings and explanations of the three different types of levers

21. Wheel and Axle: two circular objects fastened together and that rotate on a common axis

22. - always rotate together - Ex. doorknob, steering wheel

23. Pulley: a wheel that has a rope or chain passing over it; used to change the direction of the force that’s applied to the object Example: flagpole, window blinds

24. Inclined Plane: a ramp or slope that reduces the force you need to lift something

25. - Inclined planes decrease the effort force Ex. ramps

26. Screw: an inclined plane wrapped around a cylinder to make a spiral  Threads: the ridges spiraling around the screw  Ex. Screw, jar lid

27. Wedge: an inclined plane that moves Ex. Axes, chisels, knives, hatchets

28. Simple Machines in Your Body…  Your tendons and muscles pull on your bones and make them act as levers  incisors (front teeth) are wedges

29. Compound Machines: a combination of simple machines that makes it possible to do something that one simple machine alone cannot do

30. Ex. Can opener The handles are levers; the crank is a wheel and axle; a gear is then turned, which turns another gear which moves the blade which is a wedge

31. Mechanical Advantage= output force input force  Tells you how much force is multiplied

32. The larger the mechanical advantage, the more help the machine provides

33. When we calculate mechanical advantage we look at ideal situations  An “ideal” machine would be 100% efficient  100% efficiency NEVER happens in practice

34. Whenever work is done; some energy will be lost as heat Efficiency looks at this heat/energy loss

35. Efficiency = actual mechanical advantage theoretical mechanical advantage

36. OR Efficiency = output work input work X 100 %

37. Even the best designed engines are about 35% efficient