Work

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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.

• 1 J (Joule) = 0,1020 kpm = 2.778x10^-7 kWh = 2.389x10^-4 kcal = 0.7376 ft lb_f = 1 (kg m²)/s² = 1 watt second = 1 Nm = 1 ft lb = 9.478x10^-4 Btu
• 1 ft lb_f (foot pound force) = 1.3558 J = 0.1383 kp m = 3.766x10^-7 kWh = 3.238x10^-4 kcal = 1.285x10^-3 Btu

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

Example - Constant Force

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)

Example - Spring Force

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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Related Topics

• Dynamics - Dynamics Motion - velocity and acceleration
• Mechanics - Kinematics, forces, vectors, motion, momentum, energy and the dynamics of objects
• Thermodynamics - The effects of work, heat and energy on a system

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