Rust Requires Oxygen

Equipment Needed

Steel Wool
1 pencil
1 rubber band
1 large mug or cup, tall enough for a pencil to fit inside it
1 dish of water

The Experiment

Moisten some steel wool.

Use the rubberband to fasten it to the top of the pencil (Fig 1).

Arrange the pencil and the steel wool in the cup, placed upside down in the dish, as shown in Fig 2.

Make a mark on the side of the cup to show the water level.

Leave everything in a safe place for a few days.

After that time has elapsed, go back and look at your experiment.

You will notice that the steel wool has begun to rust.

You will also find that the level of water inside the cup has risen (Fig 3).

How It Works

When the steel wool rusts, it uses oxygen from the air. This causes the air pressure around it to decrease. The air outside the cup forces the water up to offset the area of low pressure inside the cup.