* The tides. The tides are the rise and fall of sea levels caused by the gravitational pull of the moon and sun. They ebb and flow twice a day, with high tide occurring when the moon is directly overhead or underfoot, and low tide occurring when the moon is at right angles to the Earth.

* The wind. The wind is the movement of air caused by differences in air pressure. It can be strong or weak, and it can come from any direction. The wind ebbs and flows as the air pressure changes.

* The waves. Waves are caused by the wind blowing over the water. They can be large or small, and they can travel great distances. Waves ebb and flow as the wind changes speed and direction.

* The seasons. The seasons are caused by the Earth's tilt on its axis as it orbits the sun. The seasons ebb and flow as the Earth moves around the sun, with spring, summer, fall, and winter occurring as the Earth's position changes.

* Human emotions. Human emotions can also ebb and flow. We can feel happy, sad, angry, or scared at different times, and these emotions can change quickly or gradually. Our emotions ebb and flow as we react to the events in our lives.