Why a sattellite is said to be in free fall?

Answer 1

Imagine firing a handgun while standing on earth with no one or thing around for the bullet to hit. The bullet will speed out of the gun, and as it moves it will trace out a curve as it gradually gets pulled to earth by the earth's gravity, and loses speed because of air resistance. It wil then fall to earth perhaps several hundred yards away. Now imagine climbing up a tall tower and doing the same thing with a high velocity rifle. The bullet will travel faster from the rifle than from the handgun but will still eventually fall to the ground under gravity and slow down because of air resistance, but in this case, the bullet might travel a mile or two before falling to the ground, and the curve its path of flight traces out will be much larger. Now imagine the satellite. When launched, the satellite travels fast like the bullet, but it will not slow down like the bullet because, as the satellite is launched into space, there is no air resistance as there is no air there. Similarly the speed at which the satellite is launched is sufficient for it to continue to fall to earth, just like the bullet, but in the satellite's case the curve it traces out is exactly the same as the curve of the earth. So, the satellite continues to freefall to earth, just like the bullets, but as the curve of the earth is exactly the same as the curve of the satellite's path, the satellite will never reach the earth. It's as if the earth was 'moving away' from the satellite as fast as it was falling towards it. This is what is meant by 'going into orbit' and it is why satellites and spacecraft have to escape the earth at great speed if they are to go into orbit. If they did not have the speed required (called the 'escape velocity') their curve of trajectory would be too small and they would fall back to earth before going into orbit.