Gravitational Fields

We describe this interaction using a gravitational field — a region of space in which an object with mass experiences a gravitational force. Earth produces a field around it, so an object placed in that field is attracted towards Earth.

All matter produces a gravitational field

Mass is a measure of the amount of matter in an object. Every object with mass has a gravitational field, whether it is a star, a planet, a person or a book. Another mass within that field experiences an attractive force.

The attraction is mutual: Earth attracts a falling object, and the object also attracts Earth. Gravity always pulls masses towards one another; it does not push them apart.

Why massive objects have stronger fields

Gravitational field strength describes how much gravitational force acts on each kilogram of mass at a particular position. A stronger field produces a greater force on the same object.

At the same distance from their centres, an object with greater mass produces a stronger gravitational field than an object with less mass. Planets and stars have enormous masses, so their gravitational effects are much more noticeable than those of everyday objects. Two books attract one another gravitationally, but the attraction is too weak to notice in ordinary circumstances.

The comparison keeps the nearby object and its distance the same. This allows the stronger attraction to be linked to the greater mass producing the field, rather than to a change in the object being attracted.

Gravity beyond Earth

Gravity is not unique to Earth. The Sun produces a gravitational field that attracts Earth and keeps it in orbit around the Sun. Other planets also have gravitational fields, but their field strengths differ. When comparing conditions at their surfaces, both the planet’s mass and its radius matter; greater mass alone is not enough to rank their surface field strengths.