The moon formed roughly 4.5 billion years ago when a Mars-sized object (named Theia) collided with a proto-Earth. However, since the proto-Earth experienced many giant-impacts, several moons are expected to possess formed in orbit around it over time. The question thus arises, what happened to those moons? Raising this very question, a team a world team of scientist conducted a study during which they suggest that these "moonlets" could have eventually crashed back to Earth, leaving only the one we see today.

Why is that the moon not falling on earth?

We know that gravity gets weaker as you go further out into the space. The earth’s gravity is far weaker at the moon than at a low earth orbiting satellite.

Remember, the moon does fall towards the planet, but the force by which the moon stays within the orbit is well greater than the gravity. The moon has an orbital speed from the momentum gained during its revolution that permits it to fall round the Earth with a trajectory that follows the identical curve as Earth’s surface. Because there paths are parallel, the moon perpetually falls at the planet without ever touching it.

We can better say that moon includes a high tangential velocity. The gravity of the planet provides the mandatory force which bends the high velocity vector continuously and keeps the moon in its orbit. The moon is really accelerating towards the planet, but its high tangential velocity keeps it from falling to the planet.

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