Suppose someone asked you to lift a hippopotamus! It sounds impossible, but with a simple machine called a pulley, you could do it.
A pulley is a special kind of wheel and axle. A rope or steel cable fits around the rim of the wheel. When one end of the rope is pulled down, the rope slides over the wheel, which turns on the axle. Then the load at the other end moves up.
With one pulley, the load moves up as far as you pull the rope down. You work just as hard to pull the rope as you would to pick up the load, but you can pull in a direction that is easier for you.
With two pulleys, you can make lifting even easier. The second pulley is attached to the thing you lift. Each part of the rope between the pulleys holds half the weight, so you pull only half as hard to move the load. But the load is held up by twice as much rope. So you will have to pull the rope twice as far as the distance you want the load to move.
The more pulleys you use, the easier it is to lift a load. But you will have to pull more and more rope. You might be able to lift that hippopotamus with a great number of pulleys, but you will have to pull a lot of rope!
Picture Credit : Google