The following notes are NOT in your textbook!
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
Examples of simple machines
We will focus on inclined planes and pulleys
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
Less force applied over a longer distance
• 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
• 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
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
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
(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
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)
• Each group will need: 10 Newton spring scale, 200 gram mass, 500 gram mass, string, metric
1 pulley, 1 s-hook
1 pulley, 1 s-hook
2 single pulleys, 2 s-
2 double pulleys, 2 s-