# Gravitational field & Gravitational field strength

Show/Hide Sub-topics (Mass, Weight and Density | O Level)

## Gravitational Force

Any two bodies in the universe attract each other with a force. This spectacle is called the gravitational attraction. This force of attraction is known as the gravitational force or force due to gravity.

A force field is a region in which a body experiences a force as a result of the presence of some other body or bodies.

• A force field is thus a method of representing the way in which bodies are able to influence each other.

## Gravitational Field

A gravitational field is a region in which a mass experiences a force due to gravitational attraction.

• A gravitational field is a region of space surrounding a body that has the property of mass. In this region, any other body that has mass will experience a force of attraction.
• All bodies near the surface of Earth experience gravitation attraction exerted by Earth.
• You experience weight on Earth due to the Earth exerting gravitational force on you. The formula to calculate weight is stated below.

## Gravitational Field Strength

ALL objects set up a gravitational field around itself. If a second body is placed at distance X from the first body, it will experience a gravitational attractive force towards the first body.

The gravitational field strength (g) at any point in a gravitational field is the gravitational force per unit mass exerted on any body placed at that point.

• SI unit of gravitational field strength is newton per kilogram. ($\text{N kg}^{-1}$)

$$F_{g} = mg$$

where

$F_{g}$ = gravitational force (unit is N),

m = mass (unit is kg),

g = gravitational field strength

Its direction is towards the massive body, such as Earth, that sets up the force field.

The gravitational field strength on Earth is approximately $10\text{ N kg}^{-1}$, while the gravitational field strength on the Moon is only $\frac{1}{6}$ of that on Earth. Hence, you will only feel $\frac{1}{6}$ of your weight on the Moon.

Example: Gravitational force on a 5 kg object is $5 \times 10 \: = \: 50 N$