Final answer:
The Moon appears to have only one side because its rotational period is the same as its period of revolution.
Step-by-step explanation:
The reason why we only see one side of the Moon is because its rotational period is equal to the period of revolution. This means that it takes the Moon the same amount of time to rotate on its axis as it does to orbit around the Earth. As a result, the same side of the Moon always faces us, and we never see the other side.