In everyday life, the terms mass and weight are interchangeable. However, in physics mass and weight do not mean the same.

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Mass is a measure of how much matter there is in an object, while weight is a measure of the size of the pull of gravity on the object.

Mass is the amount of matter in an object. Mass is measured in kilograms (kg).

Weight is a force due to the pull of gravity on an object. Weight is a force and so is measured in newtons (N).

**Gravitational field strength**

On earth, the downward force of gravity on a 1 kg mass is 10 N.

This is called the gravitational field strength (g).

Gravitational field strength g = 10 N/kg

The relationship between the weight of an object in N, its mass in kg and the gravitational field strength N/kg is given by the equation:

**weight W in N = mass m x gravitational field strength g**

W = mg

W = weight in N

m = mass in kg

g = gravitational field strength in N/kg

g = 10 N/kg

A mass of 1 kg has a weight of 10 N.

A mass of 6 kg has a weight of 60 N.

An average apple has a mass of 100 g or 0.1 kg.

The weight of the apple is:

W = mg

m = 100 g = 0.1 kg

g = gravitational field strength g = 10 N/kg

W = 0.1 kg x 10 N/kg

W = 1 N

So, a force of 1 N is the force need to lift an average sized apple off the ground.

W = weight

m = mass

g = gravitational field strength

W = mg | W = m x g |

m = | m = W ÷ g |

g = | g = W ÷ m |