The Gravitational Field

A gravitational field is a model used to explain the gravitational attraction that a massive body exerts in the space around itself on another massive body.

Objects fall to the ground due to the gravitational attraction that Earth exerts on them. This attractive force acts even where there is no direct contact between the objects and Earth. This is because those objects are in the gravitational field of the Earth.

We can't see or touch this field, but we can visualize it using field lines. The direction of the field lines provides the direction of the attractive force that a mass placed at a point in the field would perceive. The density of the field lines is an indication of the strength of the field: the denser they are, the stronger the gravitational field.

In the case of Earth (see Fig. 1), the field lines are directed towards its center, because at any point in the Earth's field, a body will feel a force directed towards the center of the Earth. The field lines become further apart from each other as the distance from the Earth increases, indicating that the field becomes weaker.

Figure 1: Representation of the gravitational field of Earth.

Near the earth's surface, the field lines appear as in Fig. 2:

• They are directed downwards, in the direction of the gravitational attraction that a body would feel near the Earth's surface.

• They are parallel and equidistant indicating that the field is uniform.

Figure 2: Representation of the gravitational field on the Earth's surface.

A couple of important points to note about the field lines:

1. Field lines do not start or stop in empty space. They end on a mass and extend back all the way to infinity.

2. Field lines never cross. If they did, then an object placed at the point where they crossed would feel forces in more than one direction.