# work and power

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Work done and energy transferred are measured in joules (J). 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. Power is a measure of how quickly work is being done.

# Weight and mass

Weight is not the same as mass. Mass is a measure of how much stuff is in an object. Weight is a force acting on that stuff.

Weight is the result of gravity. The Earth's gravity attracts objects towards the centre of the Earth and you feel forces like this as weight.

Here is the equation that links weight, mass and gravitational field strength

weight = mass × gravitational field strength

• Weight is measured in newtons, N
• Mass is measured in kilograms, kg
• The gravitational field strength is measured in newtons per kilogram, N/kg

For example, the gravitational field strength is:

• 10 N/kg on Earth
• 1.6 N/kg on the Moon

You would weigh less on the Moon because the gravitational field strength of the Moon is about one-sixth of that of the Earth. But note that your mass would stay the same. For example, what is the weight of an 80 kg person on Earth and on…