Why is it easier (and faster) to ride a bicycle somewhere than it is to walk or run? How come it's easier to lift something by using a set of pulleys? To answer these questions, you need to understand a little about simple machines.
A web site about the inventor Leonardo da Vinci has a page that will help get started:
To learn more about simple machines, look for these books:
The Science Book of Machines,
by Neil Ardley,
Harcourt, Brace, and Company, 1992
Simple Machines,
by Anne Horvatic,
Penguin: Dutton, 1989
All original text, graphics, and art © 1998 Stephen Kramer and Richard Torrey