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How do force, speed and Newton's laws explain how athletes move and change motion in sport?

Apply the concepts of force, speed and Newton's laws of motion to sporting actions

A focused answer to the O-Level ESS outcome on force and motion. Force, speed, and Newton's three laws of motion applied to sprinting, throwing and contact in sport.

Generated by Claude Opus 4.89 min answer

Reviewed by: AI editorial process; not yet individually human-reviewed

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  1. What this dot point is asking
  2. The answer
  3. Examples in context
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What this dot point is asking

SEAB wants you to apply the ideas of force, speed and Newton's three laws of motion to sporting actions. The central idea is that movement in sport obeys simple physics: forces change motion, and understanding how lets you explain sprinting, throwing, jumping and collisions.

The answer

Force and speed

A force is a push or a pull that can start, stop, speed up, slow down or change the direction of an object. In sport, muscles generate forces that move the body and implements.

Speed is how fast something moves, calculated as distance divided by time:

speed=distancetime\text{speed} = \frac{\text{distance}}{\text{time}}

measured in metres per second. Acceleration is the rate at which speed changes, which is what a force produces.

Newton's three laws of motion

Newton's laws describe how forces change motion.

  • First law (inertia): an object stays at rest, or keeps moving at constant velocity, unless a resultant force acts on it. A stationary ball stays still until kicked.
  • Second law: the acceleration of an object is proportional to the resultant force and inversely proportional to its mass, written F=maF = ma. Kick a ball harder and it accelerates more; the same kick accelerates a light ball more than a heavy one.
  • Third law: for every action there is an equal and opposite reaction. A sprinter pushes back and down on the ground, and the ground pushes the sprinter forwards and up with an equal force.

Applying the laws in sport

The laws explain technique. A sprinter drives hard against the blocks (third law) so the reaction force accelerates them forwards; a thrower applies a large force over a long range to maximise the implement's acceleration (second law); a goalkeeper must apply a force to stop a moving ball, which would otherwise keep going (first law).

Examples in context

Example 1. A sprinter exploding from the blocks. The athlete drives their legs backwards and downwards against the blocks; by Newton's third law the blocks push back with an equal and opposite force that accelerates the sprinter forwards. A more forceful drive means a larger reaction force and, by the second law, a faster start.

Example 2. A goalkeeper catching a powerful shot. The ball would keep moving by the first law, so the keeper must apply a force to stop it. By bringing the hands back as they catch (increasing the time), they reduce the force needed and the sting, applying the relationship between force, mass and changing motion.

Try this

  • Cue. Calculate the average speed of a swimmer who covers 50 m in 25 s. (speed=50/25=2 m s−1\text{speed} = 50 / 25 = 2\ \text{m s}^{-1}.)

  • Cue. State Newton's third law and give a sporting example. (For every action there is an equal and opposite reaction; a swimmer pushes water backwards and is pushed forwards.)

  • Cue. Explain, using F=maF = ma, why a player can kick a light ball faster than a heavy medicine ball with the same effort. (For the same force, acceleration is inversely proportional to mass, so the lighter ball accelerates more and leaves the foot faster.)

Exam-style practice questions

Practice questions written in the style of SEAB exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.

Original6 marksState Newton's three laws of motion and give a sporting example of each.
Show worked answer →

First law (inertia): an object stays at rest, or moves at constant velocity, unless acted on by a resultant force. Example: a hockey ball stays still on the pitch until a player strikes it with the stick.

Second law: the acceleration of an object is proportional to the resultant force and inversely proportional to its mass (F=maF = ma). Example: a footballer who kicks the ball harder (more force) gives it greater acceleration.

Third law: for every action there is an equal and opposite reaction. Example: a sprinter pushes back on the blocks and the blocks push the sprinter forwards with an equal and opposite force.

What markers reward: each law stated correctly and a clear, distinct sporting example for each (an object at rest until struck, more force giving more acceleration, and an equal and opposite reaction).

Original5 marksA sprinter runs 100 m100\ \text{m} in 12.5 s12.5\ \text{s}. Calculate their average speed, and explain how Newton's second law relates the force they apply to their acceleration.
Show worked answer →

Average speed: speed=distancetime=10012.5=8 m s−1\text{speed} = \dfrac{\text{distance}}{\text{time}} = \dfrac{100}{12.5} = 8\ \text{m s}^{-1}.

Newton's second law states F=maF = ma, so for a given body mass the greater the resultant force the sprinter applies against the ground, the greater their acceleration. A more powerful drive produces a larger force and therefore a quicker acceleration from the blocks.

What markers reward: the correct use of speed=distance/time\text{speed} = \text{distance}/\text{time} giving 8 m s−18\ \text{m s}^{-1} with units, and a correct link from F=maF = ma to greater force producing greater acceleration for a fixed mass.

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