7.2.2

# Gravitational Field Strength

Test yourself

## Gravitational Field Lines

The gravitational field lines around a point mass or spherical mass are radial.

### Point mass

• The diagram shows the gravitational field lines around a point mass.
• The field lines are all pointing towards the mass because gravitational forces are attractive.
• The lines indicate the direction of the gravitational force on another point mass, placed near to first.

### Spherical mass

• The diagram shows the gravitational field lines around a spherical planet.
• All of the field lines seem to be pointing towards the centre of the planet.

### Close to the surface of Earth

• Close to the surface of the planet and over a small distance, the field lines seem to be equally spaced and parallel.
• This is why, in our everyday experience, we think that the Earth’s gravitational field is uniform.

## Gravitational Field Strength

Gravitational field strength, g, is the same as the acceleration due to gravity.

### Field strength

• Gravitational field strength, g , is defined by the relationship:
• $g = \frac{F}{m}$
• Where F is the gravitational force on the object and m is the mass of the object.