BIOMECHANICS

Types of motion

Definitions:

Motion: movement occurs when an object has changed position in space and in time due to the application of forces

§  linear motion – where movement is along a straight or curved line, there is no rotation, and all body parts move in the same direction at the same speed (e.g. an ice skater gliding after they completed movement or a cyclist who stops pedalling)

§  angular motion – where all the parts of a body move through a rotational pathway, through the same angle, in the same direction and at the same time (e.g. when a gymnast performs a giant circle on a bar, the entire body rotates, with the axis of rotation passing through the centre of the bar)

§  general motion – combination of linear and angular motion (when defining by itself definition of linear and angular motion is required) (e.g. cyclist moving in a straight line in result of the rotation of the legs about the hip joint)

§  projectile motion – a projective is an object propelled into the air or water and affected only by the forces of gravity and air resistance

·       application of linear motion to sport in relation to:

§  speed

Measure of the distance an object travels per unit of time

Representative of how quickly you cover a given distance

Calculated by dividing distance travelled by the time taken

§  velocity

Speed in a given direction

Calculated by dividing displacement travelled by the time taken

A change in velocity could be representative of a change in speed, change in direction, or both

So if the direction of the moving body changes then the velocity changes, even though the speed might stay the same

§  acceleration

The rate at which the velocity of a body changes with the respect to time

·       Positive acceleration: Velocity is increasing

·       Negative acceleration: Velocity is decreasing

·       Zero acceleration: No change in velocity

Newtons Laws

·       definition of Newton’s First, Second and Third Laws of Motion, and how they apply to sporting contexts

Newtons first law: Law of inertia: an object in motion will stay in motion unless acted on by another force

Sporting Example:

Create a movement: netball with remain in the hands of a player until they apply force to the ball to pass it to a teammate.

Change a movement: once thrown, the netball will continue travelling at constant velocity in the direction thrown until caught by another player, when the ball’s velocity will decrease

Newtons second law: The acceleration of a body is proportional to the force applied to it and inversely proportional to the objects mass (F=MA)

Sporting example: a netball shooter uses newton’s second law of motion to judge the size of the force needed to give the correct change in momentum to the ball

Newtons third law: for every action there is an equal and opposite reaction

Sporting example: swimmer pushing of the wall after a tumble turn

Balance

·       definition of the principle of balance and how it applies to sport in relation to:

The ability to neutralise forces that disturb equilibrium

§  base of support

The greater the base of support, the greater the degree of stability.

§  height of centre of gravity

The higher the centre of gravity above the base of support, the less table the object is.

§  line of centre of gravity

The closer the line of gravity is to the limits of the base of support, the less degree of stability of the object. Movement is easier when the line of gravity falls outside the objects base of support.

§  mass

The greater the mass of an object, the greater its stability will be, given that all other factors are equal (e.g. sumo wrestling).

§  static balance

The ability to hold a stationary position (e.g. completing a handstand or staying still on a block)

§  dynamic balance

The ability to hold a position to execute an outcome (e.g. catching a wave while surfing, riding a skateboard, kicking a ball in soccer)

Projectile Motion

Definition: a projectile is an object propelled into the air or water and affected only by the forces of gravity and air resistance.

·       application of projectile motion to sport in relation to:

optimal projection

parabolic trajectory

Horizontal component: Affected by air resistance and relates specifically to the horizontal distance covered by a projectile

Vertical component: Affected by gravity and relates specifically to the height reached by the projectile

Release of projectiles

o   angle – theoretical angle for release is 45 degrees provided the height of release and landing height remain equal and spin and air resistance is not present. Angles over 45 degrees results in shorter horizontal distances, greater vertical distance and longer flight times (e.g. high jump, pole vault and American football). Angles less than 45 degrees result in shorter horizontal distances, shorter vertical times and shorter flight times (e.g. throwing a softball, cricket ball or rugby pass)

o   velocity – the greater the speed or velocity of release, the greater the distance a projectile will carry. Release speed is the most critical factor when maximising the distance travelled. The projectile’s velocity at the instant release will determine the height + length of the trajectory provided all other factors are held constant

o   height – the greater the height of release of a projectile, the greater the horizontal distance it will cover, provided all other factors are equal. When the projectile is released from the same level at which it lands, the time for the projectile to reach its peaks equals the time it takes to land. When projectile is released from a lower position at which it lands, the time taken for the projectile to reach its peak is greater than the time taken to land. When the projectile is released from a higher position it than which it lands, the time for the projectile to reach its peak is less than the time it takes to land

Levers

Definition of 3 classes of levers:

Axis (fulcrum)

Resistance (load)

Force (effort)

Key terminology:

Fulcrum/axis – The point around which the lever rotates

Effort/force arm – the distance between the fulcrum and the point at which the force is applied

Resistance arm – the distance between the fulcrum and the centre of the resistance

Input (effort) force – force exerted on the lever

Output (Resistance) force – force exerted by the lever

Function of levers:

1.      Force multiplier – Increase the application of force by making the force arm longer than the resistance arm this can be done by

·       Moving the axis/fulcrum on a 1^st class lever to increase the size of the force arm

·       Creating a 2^nd class lever which naturally has a longer force arm

2.      Speed multiplier – Increase movement speed by making the resistance arm longer than the force arm achieved by

·       Moving the axis/fulcrum on a 1^st class lever to increase the size of the resistance arm

·       Creating a 3^rd class lever which naturally has a longer resistance arm

Different classes of levers:

First class lever

Definition – the axis is located in the middle, with the force and resistance on either side

Sporting example – heading a soccer ball

Function – Speed multiplier: a force can move a resistance through a greater range of motion when the force arm is shorter than the resistance arm. This creates a speed multiplier

Function – Force multiplier: a force can move an increased resistance when the force arm is longer than the resistance arm, this creates a force multiplier

Second class lever

Definition – the axis is located at the end, with the resistance in the middle and force applied at the end

·       1^st and 2^nd class levers are rare in the human body

·       An example of a 2^nd class lever is a wheelbarrow, where a large force arm ensures more strength can be applied (force multiplier)

Sporting example – Performing a push up or calf raise

Function – force multiplier

·       A force can move an increased resistance when the force arm is longer than the resistance arm

·       2^nd class levers naturally create this

Third class levers

Definition – the axis is located at one end, with the application of force in the middle and resistance applied at the opposite end

·       The most common type of lever in the human body

When looking at the human body –

·       The muscle attachment represents the application of force

·       The joint usually represents the axis

·       The weight represents the resistance