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 Solutioning 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.

Friction and force of truck

When we push a truck parked along the roadside, then the road implements a static friction force in the opposite direction of force implemented on the truck to oppose the motion of the truck. The static friction is flexible in nature, hence, the road allows only the required amount of friction force to keep the truck at rest. If we apply more force, the road applies more friction force. Hence the friction force cancels out the force applied. In short we can explain it as follows

  • The truck has a large mass therefore the static friction between the truck and the road is very high.
  • To move the car, we have to apply force more than static friction.
  • Therefore, when someone pushes the truck and the truck does not move,
  • Hence the applied force gets cancel by the frictional force which is equal in magnitude but in opposite direction.

Answer

The logic is that Action and Reaction always act on different bodies, 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 so the truck does not move. The force of friction cancel the force applied by person push. So student justification is correct

Leave a Comment

Your email address will not be published. Required fields are marked *

BOOK

Free Class