The tides are caused by the tiny changes in gravitational pulls of the Moon and Sun, as well as centrifugal forces in opposite directions. The tides on Earth are at their greatest when the three bodies are aligned, which occurs near the full and new Moons. The Earth is then extended along that line According to Ingersoll. "The water responds the greatest, but the solid Earth responds as well," he explains. "Water flowing in the oceans and rocks moving underground, both of which lose kinetic energy, are the answer. As a result, the Earth is rotating slower and the day is growing longer."