Activity: Pulleys

Talia and the tug of war.

On SCOPE's city science episode, you saw Talia use pulleys to win in a tug of war. Here’s how she did it. Watch the clip.

What you need

• Strong rope
• Two broom handles
• Four friends

What to do

You need a large open space for this experiment.

Part 1: Normal tug of war

1. Give one end of the rope to your four friends.
2. Holding the other end of the rope, walk back until the rope is stretched.
3. When everyone is ready, start pulling the rope at the same time.
4. Stop pulling the rope when either you or your friends have moved forward about five steps.

Part 2: Pulley tug of war

1. This time, ask each of your friends to hold one end of a broom handle.
2. The broom handles need to be parallel to each other, one metre apart.
3. Tie the rope to the middle of the back stick.
4. Loop the rope over and around the front stick, then under and around the back stick.
5. Once again place the rope over the front stick, but do not loop it around.
6. As in part 1, take the end of the rope and walk back until the rope is stretched.
7. When everyone is ready, begin the tug of war. You pull the rope, while your friends push the broom handles away from each other in an attempt to pull you.

Is it easier or harder than last time?

What's happening?

It is much easier to pull your friends in the second part of the experiment because you are using the power of the pulley- a simple device used by machines like elevators and cranes.

Invented by famous Greek scientist Archimedes, the pulley consists of a wheel with a groove along its edge to allow a rope or a cable to run around the wheel and change direction. Pulleys are used to reduce the amount of force needed to lift a load.

In this experiment, you have constructed a pulley at the end of the rope your four friends were holding, reducing the amount of strength you needed to pull them in your direction.

The pulley achieves this by trading distance for effort. The amount of force required is reduced, but it must act through a longer distance. So, you only needed to use half the amount of strength to pull your four friends, but it will only move them half the distance.

But that is enough to make it look like you are stronger than all of them put together!