What You Need:
Question: How do pulleys help you to do work?
1) First, tie a heavy object such as a bunch of pencils to one end of a string .
2) Then, raise the bunch of pencils off the floor by pulling directly up on the string. Notice the weight of the object as you pull up .
3) Now, put the pencil through the empty spool of thread. Then loop the string over the pencil.
4) Have your pulley pal hold the pencil and spool in the air.
5) Pull one end of the string down. Notice the weight of the object as you pull on the string and it raises into the air.
6) What do you notice about the amount of effort, or work, it takes to lift an object with a pulley?
A Scientific Explanation:
We use machines such as pulleys to make our work easier. When you lift the object without the pulley you work with one rope. When you lift with the pulley, it is like working with two ropes. One side of the rope goes up the pulley, and the other side goes down. By using a simple pulley you can divide your work in half!
Have your friend hold a second pencil with a spool of thread under the first. Loop the string around the two spools. Do the experiment again. What do you notice about the amount of work it takes? Was it harder or easier with two spools? Can you explain what happens?