Question

To move a boat ahead in water, the boatman has to push the water backwards by his oar. Explain.

Answer 1

According to Newton's third law of motion, every action has equal and opposite reaction. So if boatman wants to move the boat ahead in water, he has to push the water backwards. By pushing the water, boatman applies a force on water in backward direction. In turn, water applies the same amount of force in forward direction, moving the boat ahead.