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Work, Kinetic Energy, and
Potential Energy
The Nature of Work
– In the everyday sense, work involves
pushing, pulling, lifting, etc.
• Work – is the measure of the amount of
energy that is transferred when a
certain force acts through as certain
distance to do some job.
Work & Transfer of Energy
• 1. Horizontal Force is applied to a
dynamics cart for a certain distance –
work is done, i.e. energy is transferred
to the cart. The cart now has kinetic
• Note: When a force is applied at an
angle, cart moves horizontally. The only
force which does useful work on the cart
is Fh=Fcosq
2. Work, Energy Transfer, and
Potential Energy
e.g. lifting an object (bricks)
• When objects are lifted, work is done
i.e. a certain force is exerted through a
certain distance. Energy is used up
(transferred) to get the job done.
• But the kinetic energy of the bricks is
zero, they are at rest. Where did the
energy go? We say that it has been
transformed into “potential energy”
which is stored inside the bricks.
• Potential Energy – energy that is stored
in an object because of its condition or
• E.g. When we stretch out or push in a
spring, we do work on it (i.e. transfer
energy to it) We say this work goes
toward increasing the potential energy
of the spring.
• In general, any time work is done,
energy is transferred to an object, and
increases its kinetic or potential energy.
Formula for Calculating Work
1. Work is  to applied force.
2. Work is  to distance moved.
• 3. Work is not related to time; whether
you do a job fast or slow makes no
difference, it is still takes the same
amount of energy because it’s the same
So WFd
W = kFd
(F = Newtons, d = metres)
• Units for Work – basic unit is the Nm
(Newton metre), called a joule (J)
• 1 J = amount of work done when a force
of 1 N acts through a distance of 1 m.
This conveniently eliminates
the “k” in the equation so