The Open Door Web Site
MECHANICS
 Custom Search
Testing the Inverse Square Law of Gravitation
 Evidence to support Newton's inverse square law of gravitation can be found in Kepler's third law of planetary motion. Here we consider the orbital motion of the moon around the earth to obtain similar confirmation. The distance between the centre of the earth and the centre of the moon is about 60 times the radius of the earth. The acceleration due to gravity at the surface of the earth is 9.8ms-2 If the inverse square law is correct, then, at a distance 60 times further away from the centre of the earth, the acceleration due to gravity should be The moon experiences a centripetal acceleration due to the force of gravity. The magnitude of this acceleration is given by The radius of the moon's orbit, r, is about 3.84×108m The time period of the orbit of the moon, T = 27.3days = 2.36×106s Using these last two figures we find that the speed of the moon in its orbit is about 1023ms-1 So, using the equation for centripetal acceleration, above, gives The fact that these two figures for acceleration are the same provides convincing evidence that Newton's inverse square law of gravitation is a good theory.
 © The Open Door Team2016Any questions orproblems regardingthis site should beaddressed tothe webmaster © David Hoult 2017 Hosted By

Mechanics Index Page