Assume the earth is a perfectly smooth sphere with a constant force of gravity and there is no air resistance: Throw a ball parallel to the ground. Now throw i

Assume the earth is a perfectly smooth sphere with a constant force of gravity and there is no air resistance: Throw a ball parallel to the ground. Now throw it faster. It will land farther away than last time, right? Keep throwing it faster and faster and the ball will keep landing further and further away from you. Eventually, you throw it so fast that the ball flys through the air, all the way around the earth and lands back at your feet from behind you. You've just completed a single orbit around the earth. Keep throwing it faster and faster until the ball flies past you forever without touching the ground. This is a little hard to imagine because this speed is tremendous and something no one can really experience on earth. The ball is constantly falling away from that direction you threw it originally due to gravity. Gravity is always acting on the ball and is always acting on any satellite in space as well. Gravity doesn't change that much for how high satellites fly. However the speed of the ball is just so such that it will never change from the height you originally threw it from. Catch the ball out of the air and throw it just a little faster this time. The ball will still orbit but will pass over your head this time. The speed of the ball dictates the orbit altitude. Mass also factors in as well but not much for something so small. Grab it out of the air and keep throwing it faster and faster and eventually, the speed is able to overcome gravity and the ball leaves Earth's gravity entirely. In Low Earth Orbit, there is just enough atmosphere to provide some minor air resistance that will actually slow down that ball you threw. As the ball slows, the orbit altitude decreases. As the altitude decreases, the atmosphere gets thicker and air resistance increases which makes the ball slow even more. It gets so slow that it can't maintain an orbit any more so it lands on the surface. If you attach a small rocket engine to the back of the ball, you can occasionally turn it on to maintain the exact speed you need for that orbit. If you use the rocket engine to make the ball go faster, you can raise the orbit. Rotate the ball 180deg and now you can use the rocket engine to slow the ball to lower the orbit. Astronauts in space constantly have gravity on them but they are moving at such high speeds that gravity is not able to change their altitude. They are always "falling" just like the ball but never land. They float around inside their spacecraft because those too are falling constantly.