Suppose you took a cannon up to the top of a very high mountain. Once
there you shoot off a cannonball in a horizontal direction.
Now provided you fired the ball with a high enough velocity, the ball should
travel around the Earth (without crashing on some unsuspecting person!)
back to your mountaintop position again!!
This experiment was suggested by the great scientist
Sir Issac Newton (1643-1727). However, it took nearly three hundred
years for his idea to become real with the launch of the first
artificial satellite.