What do you think would happen if you took a massive cannon ball to the top of a high mountain and fired it horizontally?

Well, if you fire it at just the right speed (which is very fast indeed!), the ball will travel all the way round the Earth (without crashing on some unsuspecting person)and land back to your mountaintop position again!!

This experiment was suggested by the great scientist Sir Isaac Newton (1643-1727). However, it took nearly three hundred years for his idea to become real with the launch of the first artificial satellite.