Newton's Third Law. A student in elementary physics finds...

Newton's Third Law. A student in elementary physics finds himself in the middle of a large ice rink with a small but finite coefficient of friction between his feet and the ice. He has been taught Newton's Third Law. Since the law says that for every action there is an equal and opposite reaction, all forces add up to zero. Therefore he assumes that there will be no force possible to accelerate him toward the side of the rink and so he must stay at the center. (a) How do you tell him to get to the side? (b) Once he is at the edge, what do you tell him about Newton's Second and Third Laws?

Newton's Third Law. A student in elementary physics finds himself in the middle of a large ice rink with a small but finite coefficient of friction between his feet and the ice. He has been taught Newton's Third Law. Since the law says that for every action there is an equal and opposite reaction, all forces add up to zero. Therefore he assumes that there will be no force possible to accelerate him toward the side of the rink and so he must stay at the center.
(a) How do you tell him to get to the side?
(b) Once he is at the edge, what do you tell him about Newton's Second and Third Laws?

Key Concepts

Newton's Third Law

Newton's Third Law explains that every action has an equal and opposite reaction, meaning that forces always occur in pairs when two objects interact. This law is commonly misinterpreted to imply that forces cancel out, but in reality, the forces act on different objects. In the context of the problem, when the student pushes against the ice or the surrounding boundary, his action is met with an equal and opposite reaction force, which does not negate his ability to accelerate because the forces act on separate bodies.

Newton's Second Law

Newton's Second Law states that the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass (F = ma). This means that if there is a nonzero net force acting on an object, such as from friction when a person pushes against the ice, the object will accelerate. This is crucial in understanding that despite equal and opposite reaction forces, if there is an unbalanced net force, acceleration occurs.

Friction

Friction is the resistive force arising from contact between two surfaces, and even a small coefficient of friction can provide a necessary force for propulsion. In this scenario, the student can utilize the friction between his feet and the ice to push off and move towards the edge of the rink. Although the coefficient is finite and low, it still allows a net force to be generated for acceleration, thus enabling movement.

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