Gravitational force is the force of attraction between masses

Gravity attracts all masses, but you only notice it when one of the masses is really big, like a planet

This has two important effects:

• On the surface of a planet, it makes all things fall towards the ground

• It gives everything a weight

Weight and mass are not the same

• Mass is just the amount of stuff in an object. For any given object this will have the same value anywhere in the universe

• Weight is the force acting on an object due to gravity, the pull of gravitational force on the object. Close to Earth, this force is caused by the gravitational field around the Earth

• Gravitational field strength varies with location. It’s stronger the closer you are to the mass causing the field, and stronger for larger masses

• The weight of an object depends on the strength of the gravitational field at the location of the object. This means that the weight of an object changes with its location

• For example, an object has the same mass whether it’s on Earth or on the Moon-but its weight will be different. A 1kg mass will weigh less on the Moon, because the gravitational field strength is less

• Weight is a force measured in newton

• Weight is measured using a calibrated spring balance

• Mass is not a force, and is measured in kilograms with a mass balance

Mass and weight are directly proportional

• You can calculate the weight of an object if you know its mass and the strength of the gravitational field:

  Weight(N)=Mass(kg) x Gravitational Field Strength(N/kg)

• For Earth, g=9.8N/kg and for the moon its around 1.6N/kg.

• Increasing the mass of an object increases its weight. If you double the mass, the weight doubles meaning they are directly proportional(W=M)