1. WORK POWER SIMPLE MACHINES

2. I. WORK

3. 1. What is work? A force acting through a distance No work is done on the object unless the object moves and the force applied is in the direction of this movement

4. 2. How is work calculated? Work = force x distance or W = fd

5. 3. What is the unit used to measure work? Joule 1J = 1N·m = 1kg·m 2 /s 2

6. 4. What is power? The rate at which work is done, or the amount of work per unit of time

7. 5. How is power calculated? Power = work/time P = w/t Power = force x distance/time

8. 6. What is the unit used to measure power? Watt (Joule/second) 1W = 1J/s Electrical appliances and light bulbs are rated in watts (a 75W light bulb does work at the rate of 75J/s)

9. 7. What is horsepower? The standard unit for power 1hp = 746W

10. 8. What is a kilowatt? A metric unit used to measure large quantities of power 1kW = 1000W

11. II. Machines

12. 1. What is a machine? A device used to make work easier by changing the size, distance, or the direction of the force put into the machine

13. 7. What is mechanical advantage? A quantity that indicates the number of times a machine multiplies the effort force (the higher the MA, the easier it is to do the job using the machine)

14. What are the two types of mechanical advantage? Actual Mechanical Advantage – includes friction AMA = F R ÷ F E F R = resistance force F E = effort force Ideal Mechanical Advantage – does not include friction IMA = L E ÷ L R L E = effort length L R = resistance length I

15. What does a MA of 4 mean? The machine multiplies the effort force 4 times.

16. What does a MA of 1 mean? The machine does not change the effort force

17. What does an MA of < 1 mean? The machine may increase the speed at which the work is done rather than increase the force (Ex. Egg beaters)

18. There is no unit used to express MA, it is just a number written.

19. 11. What is a simple machine? One of the six basic types of machines of which all other machines are composed

20. 12. What are the 6 types of simple machines? Inclined plane Lever Wedge Screw Wheel and axle Pulley

21. 13. What is an inclined plane? A flat slanted surface Decreases the effort force but increases the effort distance The MA increases as the slant of the plane decreases

23. 14. What is a wedge? 2 inclined planes put together The wedge itself moves Ex: knife, ax, lock, zipper, nail The longer and thinner the wedge is, the less effort force is needed to overcome the resistance force (the greater the MA is)

25. 15. What is a screw? An inclined plane wrapped around a cylinder to form a spiral Decreases the effort force but increases the effort distance The closer together the threads, the longer the distance over which the effort force is exerted and the more the force is multiplied (the greater the MA is) Ex: wood screw, cork screw, nut and bolt, jar lid

27. 16. What is a lever? A bar that is free to pivot a fixed point Fulcrum – the point where the lever pivots

28. What are three classes of levers (the position of the fulcrum determines how the lever works)? 1.1 st class lever - resistance force – fulcrum – effort force - multiplies the effort force and reverses the direction of the force - Ex: crowbar, scissors, pliers, seesaw, boat oar

29. 2.2 nd class lever - fulcrum – resistance force – effort force - multiplies the effort force but does not change the direction - Ex: wheelbarrow, door, paper cutter

30. 3.3 rd class lever -Fulcrum – effort force – resistance force -Does not multiply the effort force but increases the effort distance -Ex: rake, bat, hoe, shovel, fishing pole, your arm

31. 17. What is a pulley? A rope, belt, or chain wrapped around a grooved wheel Pulleys can change the direction of the force or the amount of force

32. Fixed pulley – attached to a structure such as a wall or ceiling; changes the direction of the force but does not multiply the force or change the distance the force moves

33. Moveable pulley – the pulley is attached to the object being moved; multiplies the effort force and increases the effort distance but does not change the direction of the effort force (block and tackle)

34. Each time another pulley is added to the system, the MA increases (the MA is equal to the number of pulleys in the system)

36. 18. What is a wheel and axle? A lever that rotates in a circle Made of 2 circular objects of different sizes

37. Wheel – the larger circular object Axle – the smaller circular object The larger wheel moves through a greater distance than the axle, therefore, the force applied to the wheel is multiplied when it is transferred to the axle

38. MA depends on the radius of the wheel and the axle (if the radius of the wheel is 4 times greater than the axle, the force will be multiplied 4 times) Ex: bicycles, ferris wheels, gears, wrenches, doorknobs, steering wheels

39. 19. What is a compound machine? A combination of two or more simple machines (car, bicycle, watch, typewriter)