Lecture 7: 09/27/11
note: text in red refers to the textbook, 9
th
edition extended.
1. Uniform Circular Motion and Centripetal force
–
section
65
2. Work
If a person pushes a mass for a certain distance, it is clear that the total effort that the person puts into
the job is proportional to both the force he/she applies, as well as the distance that the object is moved.
We therefore define the work
done by a force
to be
For the moment we are assuming that the force
is a constant, and the distance
that the object
moves is in the same direction as the force.
If we assume that the work involves pushing a mass
starting from rest, the fact that we are pushing
the mass with a constant force implies that the mass will have a constant acceleration given by
Newton
’
s second law
. This acceleration will cause the block to gain velocity over time. After
the block has traveled a distance
, the magnitude of the velocity of the block will be given by
(
)
So we see that the work done by the force goes into increasing the velocity of the mass. The velocity is
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 Spring '11
 DODD
 Energy, Force, Kinetic Energy, Mass, Potential Energy, Joule

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