# Gravitational Force

**Topics:**General relativity, Gravitation, Newton's laws of motion

**Pages:**3 (521 words)

**Published:**April 21, 2013

Newton's Law of Universal Gravitation

Apples had a significant contribution

to the discovery of gravitation. The

English physicist Isaac Newton

(1642-1727) introduced the term

"gravity" after he saw an apple

falling onto the ground in his garden.

"Gravity" is the force of attraction

exerted by the earth on an object.

The moon orbits around the earth

because of gravity too. Newton later

proposed that gravity was just a

particular case of gravitation. Every

mass in the universe attracts every

other mass. This is the main idea of

Newton's Law of Universal

Gravitation.

A portrait of Issac Newton.

Courtesy of AIP Emilio Segre Visual

Archives, W.F. Meggers Collection.

The law was published in Newton's

famous work, the Principia

("Mathematical Principles of Natural

Knowledge") in 1687. It states that every

particle in the universe exerts a force

on every other particle along the line

joining their centers. The magnitude

of the force is directly proportional

to the product of the masses of the

two particles, and inversely

proportional to the square of the

distances between them.

In mathematical terms:

By team C007571, ThinkQuest2000.

where and are the masses of the two

particles,

r is the distance between the two

masses,

F is the gravitational force between

them, and

G is the universal gravitational

constant,

.

The above equation only calculates the

gravitational force of the simplest case

between two particles. What if there are

more than two? In that case, we

calculate the resultant gravitational force

on a particle by finding the vector sum of

all the gravitational forces acting on it:

By adding the unit vector to the

equation, F now processes a direction!

Interactively test the effects of

gravitation on planets!

Newton derived the relation in such a

way that F is proportional to m

because the force on a falling body

(remember the apple?) is directly

proportional to its mass by Newton's

2nd law of motion: F...

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