Biomechanics

Angular displacement

The change in angle between the starting and current positions in radians

Angular acceleration

The rate of change of angular velocity

Moment of intertia

A body’s resistance to rotational motion (I = Emr²)

What factors increase the moment of inertia?

Having a larger mass

A larger distance from the centre of the body

Angular momentum

Quantity of rotation of a body (L = Iw)

Drag

A force that resists a body’s motion in a fluid

Surface drag

Friction between the surface of an object and the fluid around it

Form drag

The impact of the fluid on the object

Lift

Upwards force acting on an object in a fluid

Factors affecting drag

Velocity of the body

Cross-sectional area of the body

Shape and surface area of the body

Mass of the body

Bernoulli principle

The principle states that a longer path causes air to travel faster. Faster air results in lower air pressure, so a pressure difference is created between the faster and slower moving air, and a gradient is formed from the slower to the faster air, causing a resultant force in that direction

1^st class lever system

Fulcrum in the middle

2^nd class lever system

Load in the middle

3^rd class lever system

Effort in the middle

Example of 1^st class lever

Elbow during extension

Example of 2^nd class lever

Ankle during plantar flexion

Example of 3^rd class lever

Knee during extension and flexion

Forces affecting motion

Muscular force

Gravity/Weight

Air resistance/Drag

Friction

Impulse

The change in force multiplied by time

Negative impulse

Impulse when a performer lands

Positive impulse

Impulse when a performer takes off

Larger net positive impulse results in?

Larger acceleration

Magnus effect

The effect on a spinning ball where the ball is rotating in the direction of air flow causes faster air and a higher pressure. This then causes the other side to have a lower relative pressure, and a pressure gradient is formed between the high → low pressure sides, so the ball will move in that direction

Three factors affecting horizontal displacement of a projectile

Angle of release

Speed of release

Height of release

Optimum angle of release for equal height release and landing

45^o

Optimum angle of release for higher release height

<45^o

Optimum angle of release for lower release height

>45^o

Factors affecting stability

Size of base of support

Body mass

Position of centre of mass

Position of line of gravity

Linear motion

The movement of the centre of gravity of an object along a straight or curved path

How to cause angular motion

Apply a force (Torque) outside the centre of mass of an object