Floating Needle Compass
Materials: ★☆☆ Easy to get from supermarket or hardware store
Difficulty: ★☆☆ Can be easily done by most teenagers
Safety: ★☆☆ Minimal safety procedures required
Categories: Magnetism
Alternative titles: Homemade Compass
Summary
By magnetizing a needle and floating it on cork in water, you can create a simple compass that aligns with Earth’s magnetic field and points toward the nearest magnetic pole.
Procedure
Rub a bar magnet over a sewing needle several times in the same direction to magnetize it.
Cut a cork into a thin circle, about 1/4 inch thick.
Use pliers to carefully push the needle through the cork so that equal lengths of the needle stick out from both sides.
Fill a glass halfway with water.
Place the cork and needle assembly onto the surface of the water so it floats.
Observe as the needle rotates and aligns with Earth’s magnetic field, pointing toward magnetic north or south.
Test the compass by bringing a magnet or steel object near it and note the changes.
Links
Variations
Try using different sizes of cork pieces to see how stability is affected.
Use a leaf instead of cork and float it in a bowl of water outdoors.
Compare results using different types of magnets for magnetizing the needle.
Safety Precautions
Needles are sharp—handle them carefully and use pliers to avoid injury.
Keep magnets away from credit cards, ID cards, floppy disks, and electronic devices, as they can be damaged.
Adult supervision recommended for younger children.
Questions to Consider
Why does the needle align with Earth’s magnetic field? (Because Earth itself acts as a giant magnet, and the magnetized needle rotates to align with its field.)
Would this compass work on a moving ship? (Not very well—the water would spill, and the floating cork would be unstable. A sturdier, low-friction bearing was needed for early sea navigation.)
How does bringing another magnet close to the compass affect it? (The nearby magnetic field interferes, pulling the needle away from Earth’s magnetic alignment.)