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Newton's Law of Universal Gravitation - Implications

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• Building on Galileo
• Recovering Kepler
• Unifying Physical Laws
• Making new predictions

Newton's Law of Universal Gravitation

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Galileo's observed that all objects fall with the same acceleration.

That observation, combined with Newton's laws of motion, requires the force of gravity between two objects to be proportional to the product of their masses.

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Newton realized very early that only an inverse square law for the dependence of gravity on distance would give elliptical orbits in accord with Kepler's laws of planetary motion.

All of Kepler's laws can be derived from Newton's laws of motion and his law of universal gravitation.

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Newton's theory of gravity unified phenomena which were previously thought to be entirely different:

• The physics of falling objects
• Kepler's laws of planetary motion
• The motion of the moon around the earth
• The tides

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Newton's theory meant that all objects in orbit around the sun --- not just planets --- should obey Kepler's laws.

Newton's theory also predicted corrections to Kepler's laws because the planets attract each other.

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For some background about Kepler's Laws of Planetary Motion, see module g30.

If you choose to click on the above link, remember that you are now in module g31 and use the navigation button () to get back.

Otherwise, just click on return.

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