Schematic illustration of the picture of children playing teeter-totter.

Pull Ups

How Can a Pulley Help Lift Objects?

 

Materials

  • 2 wire clothes hangers
  • 2 empty toilet tissue tubes
  • tap water
  • plastic shopping bag (without holes)
  • piece of string
  • adult helper

Try This

  1. Ask your adult helper to unwind both clothes hangers and slip one wire hanger through each empty toilet tissue tube.
  2. Wind the wires as they were originally.
  3. Suspend each hanger on a tree branch or horizontal pole.
  4. Pour tap water into the plastic bag.
  5. Try lifting the water-filled bag with your arm.
  6. Now lace the piece of string around the tubes (where toilet tissue was once wrapped) and tie one end to the handles of the plastic bag.
  7. Pull down on the other end of the string. What happens?

What's Going On?

The pulley made it easier for you to pull up the plastic bag of water. The top pulley helped support the bag's weight. The pulleys also changed the direction of the force needed to lift the water: it is easier to pull down than lift up.

Schematic illustration of lacing the piece of string around the tubes and tying one end to the handles of the plastic bag.