# 12.1 Gravitational Fields

## Gravitational Fields

• Generally, a force field is a region of space in which an object will experience a force
• A gravitational field, therefore, is a region of space in which any object with mass experiences a gravitational force
• The Sun, for example, creates a gravitational field around it
• The Earth, which has mass, experiences the gravitational force due to the Sun
• This gravitational force keeps the Earth in orbit around the Sun
• Additional effects of the Moon and Sun's gravitational fields can be seen on Earth, such as the cause of tides

#### Direction of a Gravitational Field

• The direction of a gravitational field can be represented as a vector, the direction of which must be determined by inspection
• The direction of the vector shows the direction of the gravitational force that would be exerted on a mass if it was placed at that position in the field
• These vectors are known as field lines (or 'lines of force'), which are represented by arrows
• Therefore, gravitational field lines also show the direction of acceleration of a mass placed in the field
• Gravitational field lines are therefore directed toward the centre of mass of a body
• This is because the gravitational force is attractive
• Therefore, masses always attract each other via the gravitational force
• The gravitational field around a point mass will be radial in shape and the field lines will always point towards the centre of mass

The direction of the gravitational field is shown by the vector field lines

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