Unit 9
Work, Power and Machines
Work and Power
What is Work?
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Work is defined (scientifically) as the
transfer of energy that occurs when a
force makes an object move.
So, if you don’t move something you
haven’t done any work. At least that’s the
way the scientific world defines work!
How are work and energy related?
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When work is done, energy is transferred.
Energy is transferred from the object that
is doing the work to the object on which
the work is performed.
However, any force that does not act in
the direction of motion is not work.
Calculating work
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There is of course a formula for
determining the amount of work being
done.
Work = Force (N) x distance (meters)
OR
W=F x d
Work is measured in a unit called the
Joule (just like Energy is measured in
Joules).
Recall calculating force
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In an earlier unit where we studied
Newton’s Laws of Motion, we were
introduced to force.
Force is a push or pull that is exerted on
an object. Force is measured in a unit
called the Newton (N) which is equal to
1 kg x m/s2. A formula we previously used
stated that Force = mass x acceleration.
Work being done
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Work is only done during the time that the
force is in contact with the object being
moved.
For example, when a bowler releases a
bowling ball, work ceases to be done the
moment that the bowler releases the ball.
Power
Power is related to work in that power is the
rate (time) that work is done.
Formula:
Power = Work/time
Power is measured in a unit called Watts
**If John and Bob both do 150 J of work, but
John does the work in 60 seconds and Bob in
90 seconds, John will have more power even
though they did the same amount of work.