Relationship Between Gravity & the Mass of the Planets or Stars

Planets orbit the sun because of the sun's mass.
••• Photos.com/Photos.com/Getty Images

The more massive a planet or star is, the stronger the gravitational force it exerts. It is this force that allows a planet or star to hold other objects in their orbit. This is summed up in Isaac Newton's Universal Law of Gravitation, which is an equation for calculating the force of gravity.

Universal Law of Gravitation

Newton's Universal Law of Gravitation is a formula for understanding the relationship of gravity between two objects. The equation is "F = G(M1)(M2)/R," where "F" is the force of gravity, "G" is the gravitational constant, the "M"s are the masses of the objects being considered, and "R" is the radius of the distance between the two objects. Thus, the more massive either object is, and the closer they are together, the stronger the force of gravity.

Solar Systems and Moons

Gravity is what keeps planets in orbit around the sun. The sun is extremely massive, thus it holds very distant objects, like the outer planets and comets, in its orbit. This can also be seen on a smaller scale, with planets keeping satellites in their orbits; the more massive a planet is, the more distant its satellites. For example, Saturn, one of the gas giants, has the most known moons. Stars themselves orbit around the center of the galaxy.

Newton's Laws

Newton's three laws of motion are also applicable for understanding the effects of gravity on the cosmic law, particularly the first and third law. The first law states that an object at rest or in motion will remain in that state until something acts on it; this explains why planets and moons stay in their orbits. The third law is that for every action, there is an opposite and equal reaction. While this is negligible when considering something like a planet affecting a star, this explains tides on Earth, which are caused by the moon's gravity.

Einstein

Newton understood how gravity worked, but not why. It wasn't until Albert Einstein's General Theory of Relativity, published in 1915, that a theory was postulated to explain the cause of gravity. Einstein showed that gravity was not a quality inherent to objects, but instead it was caused by curves in the space-time dimensions, which is what all objects rest on. Thus, even light and other massless phenomena are affected by gravity.

Related Articles

Facts on Reentry into the Earth's Atmosphere
How to Explain Gravity to a Child
The Effects of Gravity in the Solar System
Which Planet Has the Strongest Pull?
What Is Gravitational Pull?
What Is the Distance From the Sun to Mercury?
What Causes Gravity on Earth?
Characteristics of a Dwarf Planet
What Is the Difference Between Mass, Weight and Volume?
Definition of Elliptical Orbits
What Are the Similarities & Differences Between the...
What Are the Causes of Perturbations Discovered in...
How Does Gravity Cause Planets to Orbit Stars?
Why Does the Earth Rotate?
Are the Sun & Moon Planets?
Facts About Gravity for Kids
The Two Forces That Keep the Planets in Motion Around...
What Can Cause a Change in Velocity?
Differences Between Dwarf Planets, Comets, Asteroids...
Two Factors That Affect How Much Gravity Is on an Object

Dont Go!

We Have More Great Sciencing Articles!