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Work
Definition
• (p199) Energy is defined as the ability to
do work
• In Physics, we must define work simply as
the product of force and displacement.
• Work = Force × displacement
W=F×d
When is work done?
• When we do work, it is done on an object.
• If an object does not move through some
displacement, then no work is done on
that object.
• In the same way, if there is no force
acting on the object, there is no work.
• Symbol: W
• Units: Nm which is called a Joule
Special notes: part 1
1. (p200) When an object is lifted at constant
velocity, work is done against gravity. In
this case W = Fd or W = magh
2. The force used in the formula, W = Fd, is
the applied force rather than the ΣF (net
force).
3. Although work is a product of two vector
quantities, it is a scalar quantity.
Special notes: continued
4. When the force is not in the same
direction as the displacement, we must
use the component of the force that is
in the direction of the displacement.
(See example 4 p 201)
5. Work can be negative. If the force on
the object is in the opposite direction to
the motion, the work done on the object
is negative.
• See example problems p 201
3. d = 0 and since W = Fd, W = 0
4. W = Fd or W = Fxdx:
5. Note this question requires 3 steps/formulae
Work Graphs
• (add to top of p 201) The area under a F/d
graph is work: