# Gravitational Fields

## Definition

A gravitational field, similar to an electric field or a magnetic field, is a **region where masses experience a gravitational force**. Just as with electric and magnetic fields, we can draw **gravitational field diagrams** with **gravitational field lines** which indicate the path a **test mass** would take.

## Gravitational Field Strength

Gravitational field strength is **the gravitational force acting on an object per unit of mass**. It is analogous to electric field strength for electric fields.

The gravitational field strength can be calculated at a point, if the mass and force acting on a test mass at that point is known:

is the **gravitational field strength**, in newtons per kilogram.is the **#Gravitational Force**acting on the object, in newtons.is the **mass of the object**being acted on, in kilograms.

## Gravitational Force

Gravitational force is simply the proper name for **weight**, but is a more universally applicable term - especially when considering interplanetary scales. We can calculate the gravitational force between two masses using **Newton's law of universal gravitation**, an **inverse-square law** which suggests that as the distance between two masses doubles, the force between them is four times weaker.

The equivalent for an electric field is Coulomb's Law, which is used to calculate the electrostatic force between two charges.

is the **gravitational force**between the masses, in newtons.is the **gravitational constant**, approximately. and are the **masses of the two objects**, in kilograms.is the **distance between the masses**, in metres.

## Gravitational Potential

Gravitational potential at a point in a gravitational field is a **scalar** which represents **gravitational potential energy** (the gravitational counterpart to electric potential energy) **per unit of mass**. The formal definition of gravitational potential at a point is the energy required to move a **1 kilogram test mass** to that point from an infinitely far location, where the gravitational field strength would be zero. For this reason, gravitational potential is **always negative** - moving a mass in the same direction as it is being pulled by gravitational force is equivalent to negative work done.

Gravitational potential is the **gravitational counterpart to electric potential**, and both use the symbol

is the **gravitational potential**at a point, in joules per kilogram.is the **gravitational constant**, approximately. is the **work done**bringing a test mass from infinity, in joules.is the **mass**of the object brought to the point, in kilograms.