Biomechanics Y12

Momentum

Measure of the amount of motion possessed by a moving body.

Impulse

Application of force over a period of time to change the momentum of an object.

Increasing Momentum

Increase the force and time component

Decreasing Momentum

Increase the time component

Coefficient of Restitution

Measures the elasticity of the collision between an object and a given surface. Measures the amount of energy remaining in the object after the collision

Elascticity

Measure of how much rebound exists following a collision

Angular Motion

Refers to the quantity of motion possessed by a rotating body.

Moment of Inertia

Refers to the resistance of a rotating object to change its state of motion.

Third Class Levers

Axis located at one end, force in the middle and resistance at the other end.

Function of 3rd Class Levers

Serve as a speed multiplier

Speed Multiplier

The end of a lever travels a greater displacement over the same period, meaning velocity is greater at the distal end of a lever.

Balance

The ability to neutralise forces that disturb the equilibrium or the ability to maintain or hold its position

Factors affecting balance

Base of support, centre of gravity height, line of gravity position, mass of the object.

Base of support

The greater the base of support, the more balanced you will be

Height of the centre of gravity

The lower the height of the centre of gravity, the more balanced you will be

Line of gravity

The closer the line of gravity is to the middle of the base of support, the more balanced you will be.

Mass of the object

The greater the mass, the more balanced you will be

Examples of athletes that need less stability

Slips fielder, tennis player, goal keeper

Examples of athletes that need to be more stable

Sumo wrestlers, weightlifters, defenders taking a fend off

Summation of forces

How the body segments interact to meet the task’s demands. Forces acting between the segments of a body can transfer energy between segments.

Simultaneously

All body parts move at the same time to produce a force. Generally used to produce accuracy, however some methods use it to attain maximum power.

Sequentially

Sequential combination of forces produced by different parts of the body, acting together to maximise force.

Fluid Mechanics

The natural science of fluids in motion. Sometimes forces have little effect, others it has a large effect

Major Fluid Forces

Drag (horizontal impact), Lift (vertical impact)

Boundary Layer

Thin layer of air surrounding or attached to a projectile

Laminar

Smooth flow, large turbulent pocket at the back of projectile

Turbulent

Rough flow, small turbulent pocket at the back of the ball

Boundary Layer Separation

where the boundary layer breaks away from the ball

Turbulent Flow

Flow in which the velocity at any point varies erratically

Laminar flow

A type of fluid flow in which fluid moves smoothly in individual layers or streams.

Low velocity

Boundary layer clings to surface, separation well towards the rear, minor drag.

High velocity

Separation occurs further forward, drag increases

Surface roughness

Rough surfaces create turbulent boundary layers, reducing the effect of drag.

Oval Shape

Boundary layer clings to surface, separation well towards the rear, minor drag.

Round Shape

Separation occurs further forward, increased drag

Drag

Fluid friction force is generated by the interaction of a solid body with a fluid

Factors affecting drag

Velocity, frontal cross-section size, size and shape of object, density

3 Types of Drag

Pressure, Wave, Surface

Pressure Drag

Caused by the flow of fluid separating when an object moves through it.

Surface drag

Friction on the surface of the body or object as it moves through a fluid

Wave Drag

When an object in motion moves through a fluid and produces waves.

Resistance Arm

The distance from the resistance to the effort

Force Arm

The shortest perpendicular distance between a force’s line of action and an axis of rotation

Bernoulli’s Principle

Relates to the pressure created from a moving fluid over an object, whereby fast flowing fluid produces a low-pressure and slow-moving fluid produces a high-pressure area. The air particle above the wing travels a greater distance than the particle below the wing in the same amount of time. This means they are travelling at a higher velocity.

Lift

Lift only occurs in objects which are spinning or not perfectly symmetrical.

Magnus Effect

The force that acts perpendicular to the forward path of a spinning object. Used to describe the effect of rotation on an objects path. When a ball is struck with eccentric force, there is both linear and angular rotation. The rotating ball interacts with oncoming air. The resulting curve is the magnus effect.

Types of Spin

Topspin, Backspin, Sidespin

Top Spin

Causes the ball to drop/dip and travel shorter in flight, which allows for a greater margin of error when hitting. The ball can be hit with more velocity, impacting the opponent’s time to return the shot.

Backspin

This causes the ball to rise higher in the air and travel further. This applies to activites aiming to maximise distance. It can be used to help keep the ball in play in Tennis to allow time to get back in position.

Sidespin

Causes the ball to curve left or right, depending on what side of the ball spin is imparted. It can be used to curve the ball away from the opponent’s reach, or around an obstacle.