Question

Why do rivers flow down to the sea?

Answer 1

Water always moves down the slope, i.e., from higher elevation to lower elevation. And sea is always at a lower elevation. So water flow down to the sea.

Answer 2

We know that water(liquids) always flow down from a higher to a lower surface and since sea is lower than hills the above mentioned phenomenon occurs .This happens because of 2 facts:
1.Force of Gravity.
2.Liquids possessing translatory motion slip and slide against each other to flow down from a higher to a lower level.