Topic 2 of 6 · Form 5
Biomechanics
Weight, reaction, friction (spikes increase friction), air resistance (streamlining in cycling), and the effect of spin (Magnus effect – topspin dips, backspin lifts).
Notes for this topic 1 file, in order
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Newton's laws in sport
- First law: inertia – a ball stays at rest until kicked.
- Second law: F = ma – greater force gives greater acceleration.
- Third law: reaction forces – a sprinter pushes back on the blocks and is driven forward.
Forces
Weight, reaction, friction (spikes increase friction), air resistance (streamlining in cycling), and the effect of spin (Magnus effect – topspin dips, backspin lifts).
Momentum and impulse
Momentum = mass × velocity; impulse = force × time = change in momentum. Follow-through increases contact time and impulse.
Worked example: A 0.45 kg football leaves the boot at 25 m s⁻¹ from rest; contact lasts 0.01 s. Find the average force.
Change in momentum = 0.45 × 25 = 11.25 N s; F = 11.25 ÷ 0.01 = 1 125 N
Levers in the body
- First class: neck extension (fulcrum between effort and load).
- Second class: rising on the toes (load in the middle).
- Third class: most limbs, e.g. biceps curl (effort in the middle) – speed and range of movement.
Projectile motion
Distance depends on release speed, angle and height; optimum angle is 45° when release and landing heights are equal, less when the release point is higher (shot put about 40°).
Centre of mass and stability
A lower centre of mass and wider base improve stability (wrestling, rugby scrums).
Check yourself
- Which class of lever operates at the elbow during a biceps curl?
- Why does follow-through improve a shot in golf or cricket?
- Why is a shot put released at less than 45°?
Show answers
- Third class.
- It increases contact time, increasing impulse and the ball's momentum (and improves accuracy).
- The release point is above the landing point, so a slightly lower angle gives maximum distance.
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