Sci: Making a portable compass

This is a compass you could almost carry around. If you were an escaping prisoner of war, you could carry the parts with you.

What you need to make a compass.

You will need a press-stud, three steel pins and a piece of cork, as well as a bar magnet to magnetise two of the pins. A pair of pliers may be useful before you are finished, and you need a sharp knife and a cutting board to slice the cork. Check the pins with a magnet before you start, to avoid brass pins.

Take the bottom half of the press-stud, which has four holes around it, normally used for sewing it onto clothing. Using the pliers, and bending the stud as little as possible, push a pin through two of the holes. Then push a second pin through the other two holes.

Next, stroke the pins, twenty or thirty times with the same end of the bar magnet, always starting at the pointy end and going to the pinhead end (or go the other way, if you don’t like following instructions!).

The finished compass

Now the pins will be magnetised. Push the third pin up through the cork slice, and balance the press-stud on the tip of the pin. Move the pins along so the whole arrangement is balanced, and it should turn, so one end faces north, and the other end faces south.

The press-stud dome only makes a very small contact with the pin tip, giving an almost frictionless support. With gravitational forces balanced, the remaining force is the force of the earth’s magnetic field, and this lines the compass up.

The sticking-up pin could be dangerous. Put the compass somewhere safe!

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