You’re on a hike with friends. You’re having fun, chatting and laughing as you make your way along the trail. Suddenly, you realize you can’t see the trail markers any longer. You’re lost! Luckily, Jose is an experienced hiker and he’s brought his compass. As the compass always points towards the North Pole, no matter where you are, Jose guides us back in the direction of the trail on and we get home safely.
What is a compass?
A compass is an instrument that contains a magnetized pointer (a small magnet balanced on a nearly friction-less pivot point) which shows the direction of the magnetic north.
How does it work?
Earth’s inner and outer core are metal, where the inner core is solid and the outer core is liquid. The liquid outer core is constantly moving as Earth is constantly rotating. This moving metal generates a magnetic field around our planet. To be more accurate, the magnetic field is created by the rotation of Earth’s liquid outer core and the liquid iron that moves in a rotational pattern in Earth’s core.
This magnetic field has two poles – the north pole, from which the magnetic field lines emerge, then arc through space and re-enter at the other end, the south pole.
A simple way of thinking of Earth’s magnetic field is to picture a bar magnet inside the Earth.
A compass can detect this magnetic field and its needle will always point to the magnetic north.
Make your own compass
Now that we have a better understanding of how a compass work, let’s make our own.
Here’s what you need:
- A bar magnet;
- a needle, a straightened paper-clip, or other wire-like piece of steel;
- something that floats: a piece of cork, some Styrofoam, the cap from a milk jug;
- a shallow dish, such as a pie dish;
First, we need to turn the needle into a magnet. With the bar magnet’s north pole facing the needle, stroke the magnet along the needle.
Fill the shallow pie dish with about 1 inch/2.5 cm water.
Place the float in the middle of the pie dish.
Place your needle on top of the float.
Wait a while for the motion to start. Watch what happens next.
If you have a compass, you can compare the direction of the needles in the pie dish with that of the compass. They should both be pointing in the right direction.