2. What is an instrument that makes work easier called?

3. What is an instrument that makes work easier called?
a machine

4. What are the two types of work involved in using a machine?

5. What is an instrument that makes work easier called?
Work that goes into a
machine (work input) and
work that come out of
a machine (work output).

6. Describe the two types of work involved in using a hammer.

7. Describe the two types of work involved in using scissors.

8. Describe the two types of work involved in using a rolling pin.

9. Can a machine increase the work you put into it?

10. Can a machine increase the work you put into it?
No, machines can only change the factors that determine work.
work = force x distance
Either the force will be multiplied
or the distance will be multiplied
but never both at the
same time.

11. Mechanical Advantage – a quantity that measures how much a machine multiplies force or distance.

12. The mechanical advantage tells you how much the force will increase by using a particular machine. The more times a machine multiplies the input or effort force, the better the machine is.

13. When the mechanical advantage is greater than 1, the machine increases or multiplies the force you apply.

14. Machines do not increase the work you put into them
Machines do not increase the work you put into them. The work that goes into a machine can never be greater than the work that comes out of the machine.

15. mechanical advantage = output force = input distance input force output distance M.A. = Fo = di Fi do mechanical advantage = resistance force = effort distance effort force resistance distance M.A. = FR = dE FE dR The resistance force can be just the weight of the object you are trying
to move. (Weight is a force of gravity.) Mechanical advantage has no units.

16. What is the mechanical advantage of a crowbar that allows you to put 25 newtons of force into lifting a 250 newton crate?

17. What is the mechanical advantage of a crowbar that allows you to put 25 newtons of force into lifting a 250 newton crate?
M.A. = Fo Fi M.A. = 250 N = N
M.A. = FR FE M.A. = 250 N = N
How many times does the crowbar multiply the force that was put into it? (Hint: Look at the answer.)

18. What is the mechanical advantage of ramp that is 10 m long and 3 m high?

19. What is the mechanical advantage of ramp that is 10 m long and 3 m high?
M.A. = di do M.A. = 10 m = m
M.A. = dE dR M.A. = 10 m = m

20. A pulley system has a mechanical advantage of 10. a
A pulley system has a mechanical advantage of a. If a mover uses this pulley to lift a piano with a weigh of 1450 N a distance of 4 m, how much force must the mover use? b. How far will the mover pull the rope?

21. A pulley system has a mechanical advantage of 10. a
A pulley system has a mechanical advantage of a. If a mover uses this pulley to lift a piano with a weigh of 1450 N a distance of 4 m, how much force must the mover use? b. How far will the mover pull the rope?
a. M.A. = Fo Fi = N Fi Fi = N Fi = 145 N
b. M.A. = di do = di m (10)(4m) = di di = 40 m

22. Can the work that comes out of a machine be greater than the work that goes into the machine?

23. Can the work that comes out of a machine be greater than the work that goes into the machine?
No, because every machine
has some type of friction.

24. Are any actual machines 100% efficient?

25. Are any actual machines 100% efficient?
There are no machines that are 100% efficient. Every machine deals with friction…some more than others. Friction is a force that opposes motion.

26. Ideal Machines are 100% efficient.
Ideal Machines do not exist.

27. What form of energy does friction produce?

28. What form of energy does friction produce?
heat
Why? Friction opposes motion.

29. The efficiency of a machine is defined as the ratio of the output work to the input work.
efficiency = work output x 100% work input eff = Wo x 100% Wi

30. In an ideal machine… - work output equals work input
In an ideal machine… work output equals work input the efficiency is 100%.
In real machines… the efficiency is less than 100% work output is less than work input loss due to friction and heat.

31. A man uses 419 J of work in removing a nail from a piece of wood with a hammer. The hammer has a work output of 305 J. What is the efficiency of the hammer?

32. A man uses 419 J of work in removing a nail from a piece of wood with a hammer. The hammer has a work output of 305 J. What is the efficiency of the hammer?
eff = Wo x 100% Wi eff = 305 J x J eff = 72.8 %

33. John uses 39 J of energy to move four boxes with the handcart
John uses 39 J of energy to move four boxes with the handcart. The work output from the handcart is 32.4 J. What is the efficiency of the handcart?

34. eff = Wo x 100% Wi eff = 32.4 J x 100 39 J eff = 83 %
John uses 39 J of energy to move four boxes with the handcart. The work output from the handcart is 32.4 J. What is the efficiency of the handcart?
eff = Wo x 100% Wi eff = 32.4 J x J eff = 83 %

35. Moment = length  mass momentresistance = momenteffort (length  mass)resistance = (length mass)effort

36. Solve for the missing quantity.
resistance arm 5 m
effort arm ? m
45 g
22.3 g
Solve for the missing quantity.

37. resistance arm 5 m
effort arm ? m
(length  mass)resistance = (length mass)effort (45 g  5 m) = (22.3 g  X) X = m
45 g
22.3 g

38. Solve for the missing quantity.
resistance arm 3 m
effort arm ? m
38 g
13.5 g
Solve for the missing quantity.

39. resistance arm 3 m
effort arm ? m
38 g
13.5 g
(length  mass)resistance = (length mass)effort (38 g  3 m) = (13.5 g  X) X = 8.4 m

40. Energy is the ability to do work
Energy is the ability to do work. Potential Energy – energy at rest due to position, composition, or compression. Kinetic Energy – energy of motion

41. potential energy = mass  free fall acceleration  height PE = m  g  h J = kg  m/sec2  m 1 joule = 1 kg  m sec 2 g = 9.8 m/sec2

42. A rock climber climbs 63 m to the top of a cliff
A rock climber climbs 63 m to the top of a cliff. If the rock climber has a mass of 85 kg, what is the potential energy of the climber?

43. A rock climber climbs 63 m to the top of a cliff
A rock climber climbs 63 m to the top of a cliff. If the rock climber has a mass of 85 kg, what is the potential energy of the climber? PE = m  g  h PE = (85 kg)(9.8 m/sec2)( 63 m) PE = 52,479 J

44. A 1. 8 kg book sits on top of a 2. 8 m shelf
A 1.8 kg book sits on top of a 2.8 m shelf. What is the potential energy of the book?

45. A 1. 8 kg book sits on top of a 2. 8 m shelf
A 1.8 kg book sits on top of a 2.8 m shelf. What is the potential energy of the book? PE = m  g  h PE = (1.8 kg)(9.8 m/sec2)( 2.8 m) PE = J

46. Kinetic energy = ½  mass  speed squared KE = ½  m  v2 J = ½  kg  m2/sec2 1 joule = 1 kg  m sec 2

47. What is the kinetic energy of a 35 kg dog running at 2.8 m/sec?

48. KE = ½  m  v2 KE = ½  35 kg  (2.8 m/sec)2 KE = 137.2 J
What is the kinetic energy of a 35 kg dog running at 2.8 m/sec?
KE = ½  m  v2 KE = ½  35 kg  (2.8 m/sec)2 KE = J

49. What is the kinetic energy of a 1635 kg car traveling at 29 m/sec?

50. KE = ½  m  v2 KE = ½  1635 kg  (29 m/sec)2 KE = 687,517.5 J
What is the kinetic energy of a kg car traveling at 29 m/sec?
KE = ½  m  v2 KE = ½  1635 kg  (29 m/sec)2 KE = 687,517.5 J