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When a body is moved as a result of a force being applied to it, work is done.
The amount of work is the product of the applied force and the distance:
W = F s (1)
where
W = work done (J, ft lb)
F = force acting on the object (N, lb)
s = distance object moved in the direction of the force (m, ft)
The unit of work is joule, J, which is defined as the amount of work done when a force of 1 Newton acts for distance of 1 m in the direction of the force.
This is the same unit as energy.
The work done by a constant force and a spring force can be visualized as the area under the graph in distance force diagrams like

A constant force of 20 N is acting a distance of 30 m. The work done can be calculated as
W = (20 N) (30 m)
= 60 (J, Nm)
A spring is extended 40 mm by a force of 20 N. The work done can be calculated as
W = 1/2 (20 N) (0.040 m)
= 0.4 (J, Nm)
Example - Climbing Stairs, Imperial units
The work made by a person of 150 lb climbing a stair of 100 ft can be calculated as
W = (150 lb) (100 ft)
= 15,000 ft lb
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