# Weight and mass

Weight is not the same as mass. Mass is a measure of how much matter is in an object. Weight is a force acting on that . Mass resists any change in the motion of objects.

In physics, the term weight has a specific meaning - which is the force that acts on a mass due to gravity. Weight is measured in newtons. Mass is measured in kilograms.

The mass of a given object is the same everywhere, but its weight can change. We use balances to measure weights and masses.

## Gravitational field strength

Weight is the result of . The gravitational field strength of Earth is 10 N/kg (ten newtons per kilogram). This means an object with a mass of 1 kg would be attracted towards the centre of Earth by a force of 10 N. We feel forces like this as weight.

You would weigh less on the Moon because the gravitational field strength of the Moon is one-sixth of that of Earth (1.6 N/kg). But note that your mass would stay the same.

## Weight

On Earth, if you drop an object it accelerates towards the centre of the planet. The weight of an object is calculated using this equation:

weight (N) = mass (kg) × gravitational field strength (N/kg)
Question

A person has a mass of 60 kg. How much do they weigh on Earth, if the gravitational field strength is 10 N/kg?

weight = mass × gravitational field strength

weight = 60 kg × 10 N/kg

weight = 600 N

Question

How much would the same person weigh on the Moon, if the gravitational field strength is 1.6 N/kg?

weight = mass × gravitational field strength

weight = 60 kg × 1.6 N/kg

weight = 96 N

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