Work, Power, and Machines

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Chapter 9.1

• Work, Power, and Machines

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Work is defined asa quantity that measures the
effects of a force acting over a distance if
nothing gets moved from one place to another,
there is NO WORK DONE!
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Work Equation

• W F X d
• Work force x distance
• Units
• Force Newtons
• Distance meters, kilometers
• Work Joules

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Power is calculated

• Power work/time
• P __W___
• T
• and is measured in watts (W)
• make sure its a capital W

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What is a JOULE?

• Just like Newton means kg m/s2
• Joule means the same as 1 N M
• (1 Newton-Meter) meaning the amount of work done
  lifting something with a weight of 1 Newton
  through a distance of 1 meter.

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Power

• defined quantity that measures the rate at
  which work is done.
• i.e., (how fast!)
• If we both do the same work, but you do it
  faster, you are more powerful

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Mechanical Advantage

• Simply put, its how much help we get from the
  machine.
• How much the machine multiplies our
• efforts.
• Or how much it increases our distance.
• (think about how little your wrist moves when
  bat, and how wide the other end of the bat swings
  through the air.

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Mechanical Advantage Equation

• either
• output force or input
  distance
• input force output distance
• INPUT is what you do
• OUTPUT is the work that gets done,
• thanks to the machines help!

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Example Problem A crate of bananas weighing
3000 N is lifted using a pulley. If 500 N of
force is applied (the effort force), what is the
mechanical advantage of the pulley? M.A.
(mechanical advantage) Force out / Force in
So, M.A. 3000 N / 500 N 6
This means that the force needed to lift the
crate is reduced by 6 times the weight of the
crate.
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Example A screwdriver is used to open a can of
paint. The distance that the arm is moved
downward is 4 cm, while the lid moves 0.5 cm
before popping open.
M.A. distance in / distance out
M.A. 4 cm / .5 cm 8
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The Inclined Plane (Ramp or screw) - reduces the
effort force needed by increasing
the distance through which the force is applied.
10 m
2 m
The ideal mechanical advantage is equal to the
length of the run divided by the height of the
rise.
M.A. 10 m / 2 m 5
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Another way to calculate the mechanical
advantage M.A. Force out / Force in
Example A 3500 N piano is moved up a small fight
of stairs by using a ramp. If the piano movers
only push with a force of 500 N, what is the
mechanical advantage? M.A. 3500 N / 500 N 7