Question

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.

Answer 1

In Newton’s third law, two types of forces act which are known as action and reaction. In this law, two objects must be involved. Both the force i.e. action and reaction must be equal in magnitude and opposite in direction. The statement in question implies that every interaction, there is a pair of forces acting on the two interacting objects.

Complete answer:
When we push a truck parked along the roadside, the road implements a static friction force in the opposite direction of force implemented on the truck to oppose the motion or movement of the truck. The static friction is flexible in nature and hence, the road allows only the required amount of friction force to keep the truck at rest in position. If we apply more force then the road applies more friction force on the object. Hence the friction force cancels out the force which was applied.
The logic is that Action and Reaction always act on different bodies and in opposite directions, so they cannot cancel each other. When we push a massive truck, the force of friction between its tyres and the road is very large and therefore the truck does not move. The force of friction cancels the force applied by person push or force. So student justification is absolutely correct.

Additional information:
There is an equal and opposite reaction, this is a statement of Newton's third law which means action and reaction are equal and opposite. The law implies that when a first body exerts a force F on a second body, the second body will always exert a force F′ on the first body. If F is the force on the first body and F’ be the force on the second body since the forces F and F′ are equal in magnitude but opposite in direction then the force can be written as F=F’. Here F’ is the reaction and F is the reaction. For example when you hit your head on a wall accidentally, then force exerted by your head acts on the wall, at the same time the wall exerts an equal and opposite force. You can feel this reaction as pain.
Therefore, Newton's 3rd Law states that to every action, there's an equal and opposite reaction, which means action and reaction are equal and the opposite is a true statement.

Note:
In the above example, either one force may be considered the action or other force is treated as the reaction. In the field of science and technology, Newton's third law applies to things like the recoil of a gun, jet and rocket propulsion, humans walking every day, etc. this law can be violated in certain situations like non-equilibrium situations.