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Simple Machines
• Make work easier(by changing the
force, distance or direction)
–The same amount of work is done
• Include: levers, pulleys, inclined
planes, wheel & axles, wedges &
screws
Math & Machines
• Work input (by the person) = work
output (done on the object)
–Win=Wout
–Fin x din = Fout x dout
Force & Distance Example
A 1000N piano is lifted using a lever
with a 35N force. If the piano is
lifted up 0.5 m from the ground,
what is the input distance?
Mechanical Advantage
• Tells how many times the input force is
multiplied by the machine
• Shortcut for pulleys: MA = number of
strings
Efficiency
Percentage comparing work input and
work output.
Low efficiency means a lot of friction
Efficiency = Wout / Win
(times 100 to make it a %)
Sample Problem
• Happy uses a 3.5m
ramp to push a
82kg dresser into a
moving truck that is
1.2m high. What
force did Happy
have to exert?
Sample Problem
• Happy uses a 3.5m
ramp to push a
82kg dresser into a
moving truck that is
1.2m high. What
is the mechanical
advantage of the
ramp?
Sample Problem
• Happy uses a 3.5m
ramp to push a
82kg dresser into a
moving truck that is
1.2m high. If he has
to apply a force of
300N, what is
efficiency of the
ramp?
For Today
• Chapter 8 Homework #’s 7-11
• Finish and hand in:
– Lab 8.1 Muscle Up
– Lab 8.2 Levers and Pulleys