Summary

Summary — Unit VIII: Biomechanics and Sports

• Biomechanics is the science of the movement of a living body — how muscles, bones, tendons and ligaments work together — and it is part of kinesiology. It helps us understand motion in sport and improve technique, safety and performance.
• Newton's three laws of motion underpin all sporting movement. The first law (law of inertia) explains why a body stays at rest or in uniform motion until an external force acts; the second law (law of momentum), F = m × a, links force, mass and acceleration (a 2 kg discus accelerated at 20 m/s² needs a 40 N force); and the third law (law of reaction) states that every action has an equal and opposite reaction, as in a swimmer's start or a jumper driving against the ground.
• Levers in the body are made of bones (the lever), joints (the fulcrum), muscular effort and a load. There are three classes — first class (fulcrum in the middle), second class (load in the middle) and third class (effort in the middle, the most common class in the human body) — each with its own sporting applications.
• Equilibrium (stability) is a state of balance in which opposing forces cancel out. It is either static (balance at rest — all forces and torques sum to zero) or dynamic (balance during movement at constant velocity). Stability is increased by a lower centre of gravity, a wider base of support, greater weight, keeping the CG over the base, greater friction and anticipating the direction of force — summed up in the five guiding principles of stability.
• The centre of gravity (CG) is the point where the whole weight of a body is taken to act; in standing it lies near the upper pelvis (about 56.18% of height in men and 55.14% in women). Controlling the CG helps an athlete move, stop, accelerate, throw, lift and pull.
• Friction is the contact force that opposes motion between two surfaces. It is static (before motion starts) or kinetic (sliding, rolling and fluid friction, once motion has begun), and is reduced by polishing, lubricating, using wheels and ball-bearings, and streamlining. Friction is a "necessary evil" — essential for grip, braking and pushing off, yet a cause of wear, injury, wasted energy and overheating. …