# Edexcel IGCSE Physics: Double Science 复习笔记： 8.1.2 Gravitational Field Strength

### Gravitational Field Strength

• The strength of gravity on different planets after 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

• Because of weight:
• Objects stay firmly on the ground
• Objects will always fall to the ground
• Satellites are kept in orbit

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

• Both the weight of any body and the value of the gravitational field strength g differs between the surface of the Earth and the surface of other bodies in space, including the Moon because of the planet or moon's mass
• 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

• 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 (eg. 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

• On such planets such as Jupiter, an object’s mass remains the same at all points in space
• However, their weight will be a lot greater meaning for example, a human will be unable to fully stand up

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

#### Exam Tip

You do not need to remember the value of g on different planets for your exam, the value of g for Earth will be given in the exam question.