The rising and falling of the sea is known as rising tide and ebb tide. Why does the tide rise? Actually, it is the sun and the moon that are pulling the tide. When the water on one side is pulled, the other side of the sea falls.

　　The earth has a special kind of attraction known as gravitation. It is this gravitation that pulls you back when You JUMP; it is also this gravitation that attracts the sea water. When there is a strong gravitation， the tide rises; when there is a weak gravitation, the tide ebbs.