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.
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!
Courtesy of : AIP
Emilio Segre Visual
Newton's Law of Universal Gravitation has successfully explained
the observation on planetary movements made by the German astronomer
Kepler (1571-1630). It works perfectly well in the world of ordinary
experience and has dominated for about 250 years. It, however, shows
its shortcomings when explaining the unusual orbit of Mercury around
the Sun. It breaks down when the gravitational forces get very strong
or involving bodies moving at speeds near that of light. Einstein's
General Theory of Relativity of 1915, which has overcome this limitations
of Newton's Law, was able to demonstrate a better theory of gravitation.