# Balloon Compass

Going on a bushwalk in your backyard and don’t want to get lost? Be sure to pack a balloon, a magnet and a bucket of water. They’ll help to guide you in the right direction.

• Mathematics > Measurement and Geometry > Year 1 > ACMMG023
• Mathematics > Measurement and Geometry > Year 4 > ACMMG090
• Science > Physical Sciences > Year 4 > ACSSU076

## You'll need

• bar magnet
• water balloon inflated with air
• waterproof marker pen
• bucket of water
• sticky tape
• compass

## Try this

1. Using the waterproof marker pen, draw a straight line across the round, top-end of the inflated balloon.
2. Hold the bar magnet against the side of the balloon so the north pole of the magnet lines up with the line you have drawn as demonstrated in the video.
3. Use sticky tape to attach the bar magnet securely to the balloon.
4. Float the balloon in the middle of the bucket of water and observe what happens.
5. Check whether the balloon compass is pointing north using a compass.

## What's happening?

The Earth is a giant magnet, with north and south poles. The magnetic poles of the Earth do not match the geographic poles of the Earth. For example, magnetic north pole is located about 1,800 kilometres from the geographical north pole. A compass points toward the magnetic north pole and not the geographical ‘true’ north pole. Magnetic declination is the term used to describe the difference between the orientation of a compass and the geographical ‘true’ north pole.

The bar magnet (like all other magnets) has a north and a south pole. If you allow a bar magnet to move freely by suspending it on a light string or by floating it in water, the bar magnet will move to align itself with the Earth’s magnetic field. The north pole of the magnet will point to the Earth’s magnetic north pole and the south pole of the magnet will point to the Earth’s magnetic south pole.