What force keep the planets in motion?

Answer 1

Inertia is the force that causes planets to move in a straight line. The gravity of a more massive body, such as the sun, causes them to fall into orbit instead of continuing in a straight line.

Answer 2

The simple answer is "gravity", but there's a bit more to it than that.

There are two types of forces needed to keep the planets in constant revolution around the Sun. They are Centripetal forces and Centrifugal forces.

Gravity provides the necessary centripetal force.

The centrifugal force keeps the planets from falling into the Sun because of the Sun's gravitational attraction.

"Centrifugal force" is technically called a "fictitious force". Sometimes it's referred to as the centrifugal effect.Basically it is caused by the inertia of the planets.

Answer 3

The planets move in orbits that are nearly circular but not quite. They are ellipses with small eccentricity, so the orbits look like circles but with the Sun off-centre by a different amount for each planet (2.4 million kilometres for the Earth). The planets are kept in their orbits by the force of gravity from the Sun, which is very massive (330,000 times the mass of the Earth).

Answer 4

The planets stay moving because there is nothing to stop them, but the force of gravity between planet and Sun keeps it in an elliptical orbit at a nearly constant distance from the Sun.

Answer 5

Inertia