Simple machines make work easier by applying a smaller force over a greater distance. They do not reduce the total amount of work, but make the input force required less. Examples of simple machines discussed are inclined planes and pulleys. The mechanical advantage of a machine is the number of times it can multiply the input force, while efficiency compares the work output to the work input.

1. The following notes are NOT in your textbook!
Simple machines
CP Physics

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

3. Examples of simple machines
We will focus on inclined planes

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!)

5. Less force applied over a longer
distance
din
F in F out dout
Q

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
Output Distance

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
Din
ramp is 5 meters long, and
the height of the pickup
F in F out dout truck is 1.0 meter,
calculate:
500 J
Q (a) The work input
(b) The work output 300 J
(c) The AMA of the ramp 2
(d) The IMA of the ramp 5
(e) The efficiency of the ramp
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. Data table
Pulling Masses Lifting Masses Displacing Masses on Measuring Work /
an Inclined Plane Efficiency of Inclined
Plane
Mass Distance Force Height Force Height Distance Force Work Work Eff (%)
(m) (N) (m) (N) (m) (m) (N) in (J) out (J)
1.0 kg 0.5 0.25 0.25
1.0 0.5 0.5
0.5 kg 0.5 0.25 0.25
1.0 0.5 0.5
Work in = Force x Distance on inclined plane
Work out = Force x Height of lifting mass
Efficiency = (work out / work in) x 100