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.
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The truck has a large mass. Therefore, the static friction between the truck and the road is also very high. To move the car, one has to apply a force more than the static friction. Therefore, when someone pushes the truck and the truck does not move, then it can be said that the applied force in one direction is cancelled out by the frictional force of equal amount acting in the opposite direction. Therefore, the student is right in justifying that the two opposite and equal cancel each other.
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The logic given by student is not correct because two equal and opposite forces cancel each other only in the case if they act on the somebody. According to Newton’s third law action and reaction force always act on two different bodies, so they cannot cancel each other. When a massive truck is pushed then the truck may not the force applied is not sufficient to move the truck.
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