The phenomenon of tide
The water level at the shoreline rises to a maximum and the tide goes out: we talk about high tide and low tide. It takes over 12 hours from a high tide to the next one and the time of the tide varies every day. This rhythm is ruled by the moves of the moon and the sun influencing the Earth. When all three planets are in a row, the forces are added together and the tides are larger (new moon and full moon).
When the planets form a right angle, the forces act one against the other and the tides are weaker during the first and the last quarter moon.