17Calculus - Dot Product Application - Work
17Calculus
One of the major applications of the dot product is to calculate work.
Work is defined as the magnitude of a force acting on an object times the distance the object moves. Force is a vector and the only part of the vector that contributes to the work is the part in the direction the object moves. So, if we define a vector \(\vec{d}\) that points in the direction that the object moves whose magnitude is the distance moved from point \(P\) to point \(Q\) (see the figure to the right), the work, \(W\), is
\( W = \| proj_{\vec{d}} \vec{F} \| \| \vec{d} \| \)
Now, the length of the projection of vector \(\vec{F}\) onto vector \(\vec{d}\) is
\( \| proj_{\vec{d}} \vec{F} \| = \|\vec{F}\| \cos(\theta) \)
So the work equation becomes \( W = \|\vec{F}\| \cos(\theta) \| \vec{d} \| = \vec{F} \cdot \vec{d} \).
Here we have shown there are two (equivalent) equations to calculate the work.
\( W = \| proj_{\vec{d}} \vec{F} \| \| \vec{d} \| \)
\( W = \vec{F} \cdot \vec{d} \)
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