The Moon and the ocean
The rising and falling of the sea.
How it Works
The moon is what "creates" waves. The moon's gravitational force pushes and pulls the oceans waters, that creates waves. It uses centrifugal force pushes it out and the gravitational pull the waves in.
Knod, D. (1990) Image retrieved from:http://www.sac-be.com/tides_in_a_nutshell.shtml