The only reason things fall on earth is because the earth itself creates gravity, which attracts the objects to fall downwards towards its surface. The sky is part of the earth, and the earth is in space. In space, there's not much gravity, and nothing to attract the earth to fall downwards. Instead the sun creates gravity, which attracts the earth towards it. In a way the earth is falling, its falling around the sun, this is what causes the earth to rotate around the sun, which is called the earths orbit. So the gravitational attraction of the earth to the sun keeps the earth in orbit of the sun, and keeps its position in space.
The earth is actually falling through space.Think about throwing a ball.When you try to throw a ball as far away from you as you can, it travels up and away and then falls back down in an arc until it hits the ground. However, if you could throw the ball hard enough, you could throw it so far that it would go past the "edge" of the earth and miss the ground.The earth is round, so the ball would continue to fall back down in an arc but keep missing the earth. This is what happens when a rocket launches a satellite or spacecraft into orbit.Everything in orbit around the earth is actually falling around the earth. For example, the space station is falling. The astronauts in the space station are falling at the same speed so they appear to be weightless. The earth is in orbit around the sun, so it is actually falling toward the sun.It is simply traveling fast enough and far enough away that it does not hit the sun (at least not for a few billion years).
There are a lot of ways to answer this. Let's try to refine your question. Pick one of these and ask a follow up question.
First one -- "Sky" and "fall" are defined in relation to the earth. If the earth falls, the sky falls with it. The earth can't "fall" because "falling" is for something to get closer to the earth.
Or-- The earth is falling. It is going real fast. The gravity between the sun and earth results in a force that causes the earth's direction to change constantly - around the sun - in orbit. The sun is falling fast too and orbiting the galaxy. The galaxy is falling too - faster than the earth and sun and getting farther away from other galaxys. Luckily we haven't hit the floor yet. Do you really think there is a floor?
Or-- We are going up due to the big bang but we will start falling someday and the gravity from the center of the universe will cause us to fall back to where we started.
