Besides learning about equations and forces in physics class, I got an opportunity to research the physics behind everyday objects. I chose to research about a compass. Compass is a very useful object. This object is used for navigating in dense forests to the open underwater world. But what makes it work? This is when the magnetic field came in.
Imagine the earth has a bar of magnet buried inside. The magnet has a south pole pointing to the geographic north pole and a north pole pointing to the geographic south pole. This is an analogy that explains why the earth has a magnetic field.
No one really knows exactly why there’s that magnetic field. But there’s a theory on that topic. The core of the earth consists of very hot iron and because of pressure, it’s solid. The movement caused by heat from the core plus the rotation of the earth cause the liquid outside that surrounds the core to move in a rotational pattern. It’s believed that this rotational forces create a weak magnetic field and attract the end of magnets, but only lightweight magnet can rotate and point north.
The needle of the of a compass is a lightweight magnet and that’s why the north needle is attracted to the magnetic south pole, which is the geographic north pole. The needle needs to be lightweight because the magnetic field is weak. If it were to be heavier, there wouldn’t be enough force for the needle to rotate.
Hope you enjoy this mini-lesson about the physics behind a compass!