2. What is a simple machine?
• All machines are devices that make work easier
• Some do by using other energy sources: electricity, gas, etc.
• Simple machines make work easier, are often human powered,
and have minimal moving parts
4. What do simple machines do?
• They make it easier to do the SAME amount of work, but they do not
actually make the amount of work LESS – they make the input force
required to do the work less!
• For example: you may not be able to lift a snow blower onto the bed of a truck
yourself, but you could do it using a ramp
• Exert a smaller force over a greater distance
• You end up doing the same amount, or even more work (real world
has friction!)
6. Mechanical advantage
• Definition: The number of times a machine can multiply the input (or effort) force
• Actual Mechanical Advantage: It takes into account real-world factors like friction. It is
the ratio of the output force and the input force.
AMA = Output force
Input force
• Ideal Mechanical Advantage: the MA of an “ideal machine” with 100% efficiency. It is
the ratio of the distances through which the forces must move in a simple machine.
IMA = Input Distance
Input force
7. Work input & output
• The same work equation still applies…
The work that YOU put in…
Win = FinXin
The work done by the machine…
Wout = FoutXout
• Simple machines are never 100% efficient due to friction, so we
also calculate their efficiency.
Efficiency =(Wout/ Win)x 100 = (AMA / IMA) x 100
8. Simple machines: inclines
• It takes 100 N of force to pull a box
that weighs 300 N up a ramp into
the back of a pick up truck. If the
ramp is 5 meters long, and the
height of the pickup truck is 1.0
meter, calculate:
(a) The work input
(b) The work output
(c) The AMA of the ramp
(d) The IMA of the ramp
(e) The efficiency of the ramp
FFinin FFoutout
dout
Din
Θ
500 J
300 J
2
5
60%
9. Simple machines: Pulleys
• Pulleys divide the load force
over a number of ropes
• MA = # of strands that are
lifting upwards (not counting
the force you apply if you pull
down to lift the load)
10. Pulleys lab
• Each group will need: 10 Newton spring scale, 200 gram mass, 500 gram mass, string, metric
ruler
(a)
1 pulley, 1 s-hook
(b)
1 pulley, 1 s-hook
(c)
2 single pulleys, 2 s-
hooks
(d)
2 double pulleys, 2 s-
hooks