Biomechanical principles: motion (linear, angular), force, momentum, levers, projectile motion, Newton's laws of motion, the application of biomechanics to improving performance

QCE Physical Education Unit 1 covers biomechanics as the application of physics principles to human movement. This dot point covers the concepts the syllabus expects and how to apply them to specific sporting movements.

Linear and angular motion

Linear motion is movement in a straight line. A 100m sprinter's centre of mass moves linearly down the track.

Angular motion is movement around an axis. A gymnast doing a flip rotates around their centre of mass. A discus thrower rotates around their longitudinal axis before release.

Most sporting movements combine both. A long jumper has angular motion in the legs during the run-up and at takeoff, plus linear motion of the centre of mass through the jump phase, plus more angular motion (the hitch-kick) during flight.

Newton's three laws of motion

The foundational physics principles.

Newton's First Law (inertia)

An object at rest stays at rest, and an object in motion stays in motion at constant velocity, unless acted upon by a force.

Sport application. A stationary soccer ball stays at rest until kicked. A puck on ice continues moving across the rink because friction is low. A sprinter at the blocks does not move until they apply force to the blocks.

Newton's Second Law (force, mass, acceleration)

The acceleration of an object is proportional to the net force acting on it and inversely proportional to its mass:

Sport application. A heavier rugby player requires more force to accelerate than a lighter player. A discus thrower applies force over a distance to generate the discus's acceleration. The relationship between force and resulting acceleration determines power output.

Newton's Third Law (action-reaction)

For every action there is an equal and opposite reaction.

Sport application. A sprinter pushes against the ground; the ground pushes back, accelerating the runner. A swimmer pushes water backwards; the water pushes the swimmer forwards. A high jumper presses down on the ground; the ground reaction force lifts them. Action-reaction is the basis of all locomotion.

Force

Force is a push or a pull that causes a change in motion. Measured in Newtons (N).

Key force concepts in sport:

• Net force. The sum of all forces acting on an object. If forces balance, net force is zero and no acceleration occurs.
• Friction. Force opposing motion at a surface contact. Sport demands different friction characteristics - high friction at sprint spike points, low friction on a curling stone.
• Air resistance (drag). Force opposing motion through air. Significant for cyclists, runners, ski jumpers; the basis for aerodynamic equipment design.
• Ground reaction force. The force the ground exerts on the athlete in response to the athlete pushing down. Measurable with force plates.
• Buoyancy. The upward force water exerts on a submerged body. Critical for swimming biomechanics.

Momentum and impulse

Momentum is mass times velocity:

A 100 kg rugby player moving at 5 m/s has momentum of 500 kg m/s.

Impulse is force applied over time:

Impulse equals the change in momentum. To produce a large change in momentum (e.g., launching a discus, accelerating a sprinter), you can either apply a large force for a short time, or a smaller force for a longer time, or both.

Sport application. A javelin thrower's "long pull" technique applies force over a longer arm path, producing larger impulse and thus greater javelin velocity at release. A landing gymnast bends their knees to extend the time over which force is absorbed, reducing the peak force on bones and joints.

Levers

The human body is a system of levers, with bones as lever arms and joints as fulcrums.

First-class lever

Fulcrum between effort and load. Example: the neck (atlanto-occipital joint as fulcrum, neck muscles as effort, skull as load).

Second-class lever

Load between fulcrum and effort. Example: a standing calf raise (ball of foot as fulcrum, body weight as load, calf muscle as effort).

Third-class lever

Effort between fulcrum and load. Example: a biceps curl (elbow as fulcrum, biceps as effort, weight in hand as load). Most human joints work as third-class levers.

Third-class levers trade force for speed. The biceps must produce more force than the weight being lifted, but the hand moves further and faster than the muscle contracts.

Projectile motion

A projectile in flight is acted on by gravity (downward) and air resistance (opposing motion).

The three factors affecting projectile motion:

• Speed of release. Higher release speed produces longer flight.
• Angle of release. For maximum horizontal distance with no air resistance, 45 degrees is optimal. In practice, slight adjustments matter (a shot put is released from above ground, so optimal angle is around 38-42 degrees).
• Height of release. Higher release height extends flight time and thus horizontal distance.

Sport application. A long jumper aims for around 18-22 degrees release angle because their forward velocity matters more than absolute distance per unit of effort. A shot putter aims for around 38-42 degrees. A basketball free throw aims for around 50-55 degrees because backboard return is desirable.

Application to improving performance

The point of biomechanics in QCE Physical Education is to use the science to make athletes faster, stronger, or more skilled.

Examples:

• Sprinters. Analysis of ground reaction force, stride length and frequency, body angle out of the blocks. Force plates and high-speed video identify inefficiencies.
• Swimmers. Analysis of stroke mechanics (catch, pull, push, recovery) to maximise propulsion and minimise drag.
• Throwers. Analysis of release angle, speed, and height to maximise distance. Discus throwers spend years refining the spin technique.
• Gymnasts. Analysis of angular velocity, body position, and timing of movements.
• Cyclists. Analysis of pedalling technique, aerodynamic position, power output.

How this dot point applies

A typical QCE Unit 1 question asks you to apply biomechanical principles to a specific movement in a chosen physical activity. Strong responses:

1. Identify the relevant biomechanical concepts (force, momentum, levers, Newton's laws as appropriate).
2. Use precise terminology and units.
3. Apply the concepts to the movement specifically.
4. Identify what an athlete or coach could change to improve performance.

Biomechanics is one of the technical foundations of Unit 1 and is referenced in Unit 3 (tactical decisions about how to move) and Unit 4 (designing training programs that improve the biomechanical drivers of performance).