According to the third law of motion when we push on an object, the object pushes back on us with an equal and opposite force. If the object is a massive truck parked along the roadside, it will probably not move. A student justifies this by answering that the two opposite and equal forces cancel each other. Comment on this logic and explain why the truck does not move.

According to the third law of motion when we push an object, the object pushes us back with an equal and opposite force. These two forces are called as action-reaction pair.

The student’s justification is incorrect since action and reaction always operate on different bodies and hence cannot cancel each other. When two equal and opposite forces act on the same body, they cancel each other.

A truck parked on the side of the road has a heavy weight and generates greater friction between the tyres and the ground than the force applied. As a result, the truck will only move if a force greater than the friction force is applied to it.