The equation
Work Done = Force*Distance only applies when a constant force acts in the direction of movement. To find the work done when a constant force does not act in the direction in which a particle moves we use the dot product:
For, example when a particle moves from
to
under the action of the force
we first find the displacement vector from the start point to the end point:
The work done is then
The dot product
where e-d is the unit vector in the direction of
returns the component of
in the direction of(
) as shown below. Multiplying this by
gives the work done by the force.
