What did Galileo's principle of inertia state? Not all heavenly bodies revolve around Earth. The universe is centered around the Sun, not Earth. An object that is moving will keep moving until something stops it. An object that is moving needs something to keep it moving.

An object will keep moving unless a object stops it.

An object that is moving will keep moving until something stops it.

Explanation:

Galileo stated that: "A body moving on a flat surface will continue in the same direction and at constant speed unless disturbed." Although nowadays velocity is usually referred to as a vector, in Galileo's time it was still a scalar, and therefore he believed that a uniform circular motion was natural, and that a body in such motion would continue to have it until a force disturbed him.

This argument served to explain the movement of the earth around the sun, since the force of gravity came only later, with Newton. It was also with Newton that speed was written as a vector, and the principle now has the current interpretation.