Q.State Newton's third law of motion. Use it to explain how a rocket is able to accelerate itself forward even in the vacuum of outer space, where there is no air for it to push against.

Newton's third law states that whenever one body exerts a force on a second, the second exerts an equal and opposite force back on the first. A rocket engine works by burning fuel and continuously expelling the resulting hot exhaust gas out of the rear of the rocket at very high speed. In doing so, the rocket exerts a large force on this exhaust gas, pushing it backward. By Newton's third law, the exhaust gas simultaneously exerts an equal and opposite force back on the rocket, pushing it forward.\n\nThis explains a common misconception: a rocket does not need anything external -- such as the surrounding air -- to "push against" in order to move forward, unlike, say, a car's tyres pushing against the road, or a swimmer's hands pushing against the water. The entire action-reaction pair here exists purely between the rocket and the exhaust gas it itself expels; both members of the pair belong to the rocket-and-its-fuel system, and neither one involves the air at all. Consequently, a rocket engine works exactly as well -- indeed better, since there is no air resistance opposing …

Identify the actual action-reaction pair -- rocket pushes exhaust gas backward, exhaust gas pushes rocket forward -- and note that both members of this pair b …

• Believing (a very common misconception) that a rocket pushes against the surrounding air to move forward, which would wrongly predict that rockets cannot work in the vacuum of space. …