Problem
You climb the ladder and step inside. It’s your first time in your friend’s tree house. It has just about everything you could want. Except snacks! “Oh, I knew I forgot something,” says your friend.
Just then, your friend’s grandmother comes out of the house carrying two lunch bags. But how will she get them up to you?
Solution
Grandma has a rope and a bucket. She swings the rope over a tree branch. Then she ties the end of the rope to the bucket handle.
Grandma places the lunch bags in the bucket and pulls the other end of the rope. With each pull, the bucket goes higher. Soon, it reaches you. Problem solved!
It's Simple
Grandma used the rope and branch as a simple machine. Simple machines help us do work. They move things faster, farther, or more easily than we can without them.
Simple machines have no more than a few parts. Some have just one part.
In the Groove
How can a rope and a branch be a machine? Together, they form a pulley. A pulley is a wheel. It has a cord wrapped around it. The cord fits in a groove around the wheel. The wheel turns as the cord is pulled through the groove.
The branch doesn’t have a groove. It doesn’t turn like a wheel. But, the idea is the same. Grandma pulled down on one end of the rope. Then the other end moved up. The pulley made it easier to lift the bucket. It changed the direction of the force.
How to lift things with a pulley
1
Pull down on this end of the rope.
2
The rope moves through the pulley.
3
The load moves up with this end of the rope.
