How do momentum and impulse explain why follow through increases ball speed and why bending the knees softens a landing?
Define momentum and impulse and apply the impulse momentum relationship to generate force and to absorb force safely in sport
A focused answer to the WACE Year 12 Physical Education Studies Unit 3 content on momentum and impulse. Momentum as mass times velocity, impulse as force times time, the impulse momentum relationship, and how follow through generates speed while bending joints on landing reduces force for safety.
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What this dot point is asking
WACE wants the two definitions, the relationship between them, and two applications: generating speed and absorbing force. The strongest answers manipulate the relationship to explain why technique changes the force or velocity.
Momentum
Momentum is the quantity of motion a body has, calculated as mass times velocity. Because an athlete's mass is essentially fixed during a skill, momentum is changed by changing velocity. A heavier, faster rugby player carries more momentum and is harder to stop than a lighter, slower one.
Impulse
Impulse is the force applied multiplied by the time over which it acts. The impulse momentum relationship states that the impulse applied to a body equals its change in momentum. This single relationship explains both generating and absorbing force, because it can be read two ways: a force over a time produces a velocity change, and a required velocity change can be spread over a longer time to reduce the force.
Generating force: follow through
To give a ball maximum speed, the athlete maximises the impulse applied to it. Following through keeps applying force to the ball over a longer time before release or after contact, increasing the impulse. A larger impulse means a larger change in momentum, and since the ball's mass is fixed, that means a higher release velocity. This is why a long follow through in a throw, a tennis serve or a golf drive is not decoration but a way to extend the contact time and increase the impulse.
Absorbing force: safe landings and catching
When landing from a jump or catching a fast ball, the body must lose a fixed amount of momentum (stopping the motion). By increasing the time over which this happens, the force experienced is reduced, because force times time is fixed. Bending the knees, hips and ankles on landing lengthens the stopping time and lowers the peak force on the joints. Drawing the hands back while catching a hard ball does the same. This is the basis of safe technique and injury prevention.
How this maps to the exam
Questions either ask how an athlete maximises ball speed or how they reduce force on landing or catching. State the relevant definitions, quote that impulse equals change in momentum, then explain whether time is being increased to build impulse (for speed) or to reduce force (for safety).