Question

Why doesn't the Earth fall into the Sun?

Answer 1

Earth doesn't fall towards the Sun because it is in orbit.

Explanation:

When a planet is in orbit around a Sun, the distance between the planet and the Sun and the orbital period are related by Kepler's third law. If the orbital period `T` is in years and the semi major distance `a` is in AU then:

`T^2=a^3`

According to Newton's laws of motion, this is due to the gravitational attraction force between the planet and the Sun balancing the centripetal force keeping the planet in an elliptical orbit.

We now know that there is no such thing as a gravitational force. Neither is there a centripetal force for an orbiting body. General Relativity shows that the mass of the Sun, and to a lesser extent the Earth, bend spacetime. So, actually a planet in orbit is following a geodesic in spacetime. A geodesic being the four dimensional equivalent of a straight line.

Also, due to various gravitational effects, planets in orbit tend to get further away from the Sun as time passes. So, unless the Earth was slowed down by some other planet's gravity, it would never be pulled closer to the Sun.