Gravitational Field Strength (Edexcel IGCSE Physics (Modular)): Revision Note

Gravitational field strength

• The strength of gravity on different planets affects an object's weight on that planet

• Weight is defined as:

The force acting on an object due to gravitational attraction

• Planets have strong gravitational fields

  • Hence, they attract nearby masses with a strong gravitational force

• The force of weight is responsible for:

  • objects staying firmly on the ground

  • objects always falling to the ground

  • satellites being kept in orbit

Objects are attracted towards the centre of the Earth due to its gravitational field strength

• Weight and gravitational field strength both vary on the different objects in the Solar System

  • The greater the mass of the planet then the greater its gravitational field strength

  • A higher gravitational field strength means a larger attractive force towards the centre of that planet or moon

• The value of g varies with the distance from a planet, but on the surface of the planet, it is roughly the same

• However, the value of g varies dramatically for different planets and moons

• The gravitational field strength (g) on the Earth is approximately 10 N/kg

• The gravitational field strength on the surface of the Moon is less than on the Earth

  • This means it would be easier to lift a mass on the surface of the Moon than on the Earth

• The gravitational field strength on the surface of the gas giants (e.g. Jupiter and Saturn) is more than on the Earth

  • This means it would be harder to lift a mass on the gas giants than on the Earth

Value for g on the different objects in the Solar System

• The mass of an object is always the same, but its weight changes depending on the gravitational field

  • This means that on both Earth and Jupiter, an object’s mass will have the same value

  • However, their weight will be a lot greater on Jupiter than on Earth, so much so that a human would not be able to stand up on the surface of Jupiter

A person’s weight on Jupiter would be so large a human would be unable to fully stand up