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.

When we push a truck parked along the roadside, then the road applies a static friction force in the opposite direction of force applied on the truck to oppose the motion of the truck. The static friction is adjustable in nature, i.e., the road offers only the required amount of friction force to keep the truck at rest. If we apply more force, the road applies more friction force (up to the highest value, known as limiting value of static friction. Hence the friction force cancels out the force applied.Here student's justification is that the two opposite and equal forces cancel each other and hence the truck does not move. However, the action and reaction forces do not cancel each other as they act on the different bodies whereas the truck did not move due to zero net force which is balanced by the static friction of the truck.