Long before satellite navigation was invented, people relied on compasses to navigate the ocean.
A compass has a needle that always points north or south to match the Earth’s magnetic field.
An important part of this activity is magnetising the compass needle. You can use a dress pin or needles, however, any thin steel object can be used.
You will need
- Two felt tipped pens
- A plastic cup
- A plastic lid that is wider than the base of the plastic cup
- A small bowl of water
- A magnet
- A dress pin or steel needle
- Some adhesive putty
- A pair of scissors
- A smartphone
- A ruler
What to do
- Using the scissors, cut off the base of the plastic cup. This will float on the water, so the compass needle can turn
- Hold the base of the plastic cup and then find the centre of the plastic base. Use the ruler and measure one centimetre inward from the edge of the cup.
- Using a felt tipped pen, mark this measurement using a coloured dot and repeat this on the other edge of the centre of the
- Place a small rolled ball of adhesive putty beneath the cup’s base and carefully slide the pin down through one dot and up through the other
- Magnetise the pin by stroking the magnet all along the length of the pin (in one direction only) and lifting the magnet away from the end of the pin each time. Do this approximately 50 times. Always use the same end of the magnet.
- Pour water into the plastic lid, ensuring there is enough water for the plastic base of the compass to float
- Float the compass on the surface of the water (make sure the compass is not placed in strong winds, next to large metal objects, or electrical appliances).
- Observe and take note of how the compass needle turns and moves to line up with the Earth’s magnetic field.
- Use a smartphone to find ’north’. Note which end of the pin points north and mark N, S, E and W on the
- Document your project from start to finish using a video camera and share your video as part of National Science
How it works
All magnets have a magnetic field around them and two ends, or ‘poles’, where the magnetic field is strongest.
Your compass needle is made of steel, which is made up of lots of tiny crystals called ‘domains’.
Each domain is a tiny magnet, and when the needle was stroked with the magnet, all the domains lined up. Therefore, the magnetic fields point in the same direction.
The Earth’s magnetic field almost lines up with its axis of rotation, so we can use a compass to navigate.
(Copyright: Australian Science Teachers Association 2020, except where indicated otherwise. This work is licensed under a Creative Commons Attribution NonCommercial 4.0 International licence.)