Dear people of the internet. Rem-person is going to try to explain with mechanical pencil. The Sun, the Earth, the Moon and you. When the moon is full or new, the Sun and the Moon due to their positioning with the Earth have an combined force of gravity upon the Earth's water, resulting in very high tides and very low tides. Now this does not only apply to the oceans, it applies to all bodies of water large and small. However the bigger the body of water, the more you will notice it. These things are called spring tides, even though its name suggests seasons being involved it doesn't. They are just names. During quarter phases of the moon the gravity of the Moon and the Sun work against each other, resulting in smaller changes of tide, so in other words less high of high tide, and less low of low tide. This is called Neap tide. Even though the name might suggest it, it has no relation with the National Electrical Annuity Plan. Now, the Earth has a much greater pull of gravity than the moon has, but when combined with, oh lets say the centrifugal force created by the spin of a very round beautiful Earth, you get the effects of the tide. So in a way, tides prove the Earth is round.