# A small bar magnet is hidden in a fixed position inside a tennis ball. Describe an experiment that you could do to find the location of the north pole and the south pole of the magnet.

A small bar magnet is hidden in a fixed position inside a tennis ball. Describe an experiment that you could do to find the location of the north pole and the south pole of the magnet.
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Cael Cox
We need to think of a way to determine a north and south pole of a magnet by using a tennis ball with a bar magnet fixed inside.
If we understand the interaction between Earth's magnetic field and a compass, we can see that we can create a compass out of that tennis ball. By simply putting it in the water, the ball will orientate in such a way to fit the effects of the Earth's magnetic field, thus becoming a compass.
Since opposite poles attract, the south pole of the magnet bar will point towards Earth's north and magnet's north will point into Earth's south.
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The magnetic poles of this hidden magnet can be found with a compass. If we assume that the magnet is strong enough that in its vicinity of the compass the Earth's magnetic field is going to be neglectable, the needle of the compas once we put it on the ball will point towards the south magnetic pole of the bar (not north which is a common misconception, the Earth's north geographic pole is its south magnetic pole and vice versa). Now we will glide along the ball's surface until the compass starts rotating freely. That means that we have located the south magnetic pole and the north magnetic pole is on the opposite side.
Result:
For such an experiment we can use the compass.