Explain the application of the law of action and reaction in swimming and sprinting.

Concept understanding — Newtons Third Law

Newton’s Third Law: The Law of Action and Reaction

Imagine you are pushing a heavy box across the floor. You feel the box pushing back against your hands — that resistance is not your imagination. Or think of jumping off a small boat onto a dock: the boat drifts backward as you leap forward. These everyday experiences point to a deep truth about how forces work in the world.

Newton’s Third Law says: Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force back on the first. In simpler words, forces always come in pairs — you cannot push something without that something pushing back on you, with the same strength, in the opposite direction.

Important

The two forces in a Third Law pair always act on different objects. This is the most common point of confusion. The force you apply to the box acts on the box; the force the box applies to you acts on you. They are not two forces cancelling each other out — they are acting on separate bodies.

Why this matters beyond physics

For a commerce or humanities student, this law is not about equations. It is about understanding that every action has a reaction — not as a vague metaphor, but as a precise principle of how the physical world is structured. When you walk, your foot pushes backward against the ground, and the ground pushes you forward. When a rocket launches, it pushes exhaust gases downward, and those gases push the rocket upward. Nothing moves in isolation.

This idea has a powerful implication: you cannot exert a force on something without experiencing an equal force yourself. If you try to push a wall, the wall pushes you back just as hard — you feel it in your arms. If you pull a rope, the rope pulls you. Every interaction is mutual.

A few key points to remember

Forces always come in pairs. There is no such thing as a single, isolated force.
The two forces are equal in strength and opposite in direction.
They act on two different objects — never on the same object.
The pair of forces happen at the same time. There is no delay between action and reaction. …

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Newton's third law — every action has an equal and opposite reaction — explains how swimmers push water backward to move forward and sprinters drive the ground backward to accelerate forward.

Why Newton's Third Law Matters in Sport

Every movement in sport requires an athlete to generate force against something external. You cannot simply "will" yourself forward; you need a surface or medium to push against. Newton's third law states that whenever one body exerts a force on a second body, the second body exerts an equal force in the opposite direction on the first. This reciprocal pair of forces is what makes all locomotion possible. In swimming and sprinting, the athlete applies force to the environment (water or ground), and the environment applies an equal and opposite force that propels the athlete.

Understanding this principle transforms how coaches teach technique: the goal is not just to move your limbs quickly, but to apply force effectively against the medium so that the reaction force is maximized in the desired direction.

Application in Swimming

When a swimmer pulls her arm through the water during the freestyle stroke, she pushes the water backward and downward. The water, in turn, exerts an equal and opposite force on her hand and forearm — pushing her body forward and slightly upward. The larger the surface area of the hand and the faster the pull, the greater the backward force on the water and thus the greater the forward reaction force.

The same principle governs the kick. As the legs drive water backward, the water pushes the swimmer forward. Efficient swimmers angle their hands and feet to maximize the backward component of the force, ensuring that the reaction force has a strong forward component rather than being wasted in vertical or sideways motion.

Even the dive at the start illustrates the law: the swimmer pushes forcefully against the starting block, and the block pushes back with equal force, launching the swimmer into the air and forward into the water.

Tip

Swimmers often use paddles in training to increase the surface area of the hand, which increases the force applied to the water and thus the reaction force — building strength and reinforcing the feel of an effective pull.

Application in Sprinting

A sprinter accelerates by driving her foot backward and downward into the track. The track cannot move, so it exerts an equal and opposite force — forward and upward — on the sprinter's foot. This reaction force is what propels the athlete forward. The harder and more effectively the sprinter pushes against the ground, the greater the forward reaction force and the faster the acceleration.

At the start, the sprinter pushes explosively against the starting blocks. The blocks push back with equal force, driving the athlete out of the crouch and into the first strides. During the race, each foot strike is a miniature version of this exchange: the sprinter applies a force to the ground, and the ground applies an equal force that maintains or increases her speed.

Technique is crucial. If the sprinter's foot slips or if the push is directed too much vertically (jumping rather than driving forward), the reaction force is not optimally aligned with the direction of motion, and speed suffers. Elite sprinters learn to apply force at an angle that maximizes the horizontal component of the reaction. …

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Q.Explain the application of the law of action and reaction in swimming and sprinting.

Why Newton's Third Law Matters in Sport

Application in Swimming

Application in Sprinting

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