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How can we describe motion in terms of energy changes?

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Work done and energy transferred are measured in joules (J). The work done on an object can be calculated if the force and distance moved are known.

Objects raised against the force of gravity contain gravitational potential energy.

The more mass an object has and the faster it moves, the more kinetic energy it has.

# Work, force and distance

You should know and be able to use the relationship between work done, force applied and distance moved.

## Background

Work and energy are measured in the same unit, the joule (J).

change in energy (joule, J) = work done (joule, J)

## The equation

This equation shows the relationship between work done, force applied and distance moved:

work done (joules, J) = force (newtons, N) x distance (metres, m)

The distance involved is the distance moved in the direction of the applied force.

Question

A force of 10N is applied to a box to move it 2m along the floor. What is the work done on the box?

• The work done is 10 × 2 = 20J.
• The work is done on the bottom of the box and on the floor. The energy increase is shown by both of these getting hotter.

Check your understanding of this equation by having a go at the activity.

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