The Universal Law of Gravitation

  Newton’s universal law of gravitation is a fundamental aspect of modern science. The law states that every mass is attracted to every other mass through a force known as gravity. The strength of the gravitational force between any two objects is directly proportional to the product of their masses, which means that increasing the mass of one object increases the gravitational force between both objects. The force of gravity between two objects is also inversely proportional to the the square of the distance between two objects, therefore the force of gravity decreases as the distance between the two masses increases. Newton’s law of gravity extends to Kepler’s laws, as the inverse square law for gravity leads directly to elliptical orbits for planets orbiting the Sun. Newton showed that two objects attracted by gravity both orbit their common center of mass, which is the point representing the average position of mass between the two objects. For example, in a binary star system with both stars of equal mass, the center of mass lies directly between the two objects therefore the stars would orbit around themselves. However, in our Solar System, since the Sun is so much more massive than planets, the center of mass between the Sun and any planet lies inside the Sun, and as a result the planets orbit around the Sun. Prior to Newton, many people saw Kepler’s planetary model for our Solar System as just another theory. By explaining Kepler’s complex laws in terms of basic laws of physics, Newton was able fully legitimize Kepler’s theory and thus convince the world of a heliocentric Solar System.

Objects Orbit Their Common Center of Mass

2 thoughts on “The Universal Law of Gravitation”

  1. I think this blog post is very interesting because it shows that, although all planets orbit around the Sun, each planet is orbiting around a different particular point within the Sun’s interior. Since the Earth has less mass than Jupiter, its common center of mass with the Sun lies closer to the center of the Sun than Jupiter’s does. So, the center of Jupiter’s orbit is further from the center of the Sun than the center of Earth’s orbit. It is kind of cool to think that the planets do not orbit around the direct center of the Sun!


  2. Good post! Gravitational forces between masses leads to a lot of interesting behavior. Have you looked at how the orbits of multiple objects of similar masses look? Triple stars are a very interesting system to study.


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