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Proof of Equation 8-2Figure 8-4Z? shows an arbitrary round trip for a particle that is acted upon by a single force. The particle moves from an initial point a to point b along path 1, and then back to point a along path 2. The force does work on the particle as the particle moves along each path. Without worrying about where positive work is done and where negative work is done, let us just represent the work done from a to b along path 1 as
and thus
In words, the work done along the outward path must be the negative of the work done along the path back. Let us now consider the work
. Substituting which is what we set out to prove. 8-3 Determining Potential Energy Values Here we find equations that give the value of the two types of potential energy discussed in this chapter: gravitational potential energy and elastic potential energy. However, first we must find a general relation between a conservative force and the associated potential energy. Consider a particle-like object that is part of a system in which a conservative force
This equation gives the work done by the force when the object moves from point Substituting Eq. 8-5 into Eq. 8-1, we find that the change in potential energy due to the change in configuration is
This is the general relation we sought. Let's put it to use. Date: 2015-01-12; view: 1133
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