Spec PE - biomechanics ATAR YEAR 11

biomechanics

the production of motion and the effects of forces relative to the body.

benefits of biomechanics

Technique efficiency, Injury reduction, Modifications of sport usage, Technological development of equipment

3 types of motion

liner motion, angular motion and general motion

liner motion

Takes place through linear pathway, either in a curved or straight line

All parts of the body move at the same speed, in the same direction, and over the same distance

- Example: a ski jumping moving through the air in the glide phase (curved)

- Example: ice skater gliding after they completed a race (straight)

Angular motion

Takes place when objects turn about an axis of rotation

All body parts travel through the same angle, in the same direction, in the same time. (not same distance!)

Can take place around 3 different axes of rotation

- Example: 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

Example: cyclist may move in a straight line because of the rotation of the legs about the hip joint

linear motion: distance

Path of body as it moves from one location to another

linear motion: displacement

How far you finish from start point in set direction

linear motion: speed

Distance ÷ Time, doesn't tell max speed, doesn't indicate speeding up or speeding down

linear motion: velocity

Displacement ÷ Time

Given direction

linear motion: acceleration

Final velocity - initial velocity ÷ Time

- Positive - increasing

- Negative - decreasing

- Zero - no change

- Due to gravity: causes parabolic trajectory of all projectiles (9.8m/s)

- Uniform acceleration: body accelerates @ constant rate in both magnitude & direction

angular motion: vector

A quantity that has both magnitude and direction

angular motion: angular distance

The exact length of an angular path

angular motion: angular displacement

The angle between the initial and final positions of the body

angular motion: angular speed

Angular distance ÷ time

angular motion: angular velocity

Angular displacement ÷time

coordination of linear motion

Sequential vs simultaneous movement- accuracy and power summation of velocity

Types of forces

sub maximal and maximal force

sub maximal force

Less than maximal force, generally used when accuracy is most important.

maximal force

Result of perfect force summation, maximal muscle contraction and excellent technique to achieve maximal force.

summation of force- kinematic chain

Process that determines how to best use body segments depending on demands of the task. power or accuracy

summation of force: power

more segments used, forces usually sequentially summated

summation of force

less segments needed and usually summated simultaneously

force summation

Simultaneously and sequentially

force summation: simultaneously

- All body parts move at same time to produce force

- Used to produce accuracy

force summation: sequentially

- All body parts moved in sequence to produce a force

- Produce maximal force in whole body actions

Successful summation of a force

-Body parts move in sequence to generate largest force or acceleration possible.

-To sequentially produce maximal force effectively. Flowing principals need to be applied.

successful summation of force: principles

- Stronger and larger muscles of thighs and trunk are moved first followed by faster and smaller muscles

- Sequentially accelerate each body part so that optimum momentum passes from one body part to next.

- Each body part should be stable so next body part accelerates around stable base from one body part to next

- Use as many body parts as possible, so force can be applied over maximum possible time

- Follow through is important to prevent acceleration of last segment and sale dissipation of force

- Ensure all forces are directed at target

Stability

Objects resistance to movement, from a balanced position

static stability

when an object is at rest and not moving with linear or angular motion

dynamic stability

when an object is in motion and moving with linear or angular motion

balance

The ability to neutralize forces that disturb equilibrium

- Standing on one leg

- Scoping ball up on run

centre of gravity

-The point around which body weight is equally balanced in all directions

- Also, referred to as centre of mass

- Standing still, centre of gravity is in abdominal cavity

- Position changes, centre of gravity does

- The position of centre of gravity will determine if body is in balance

centre of gravity in sport

How jump and pole vault, where athletes are trying to attain maximum height, individuals will endeavour to position COG outside their body. Having it pass beneath the bar whilst their body goes above it to achieve max height

base of support

area around by the outermost regions of contact between body and support surface

Factors affecting balance and stability

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Factors affecting balance and stability: mass of object

greater mass of an object, the greater its stability will be, given that all other factors are equal

Factors affecting balance and stability: size of objects base support

greater area support, greater degree of stability

Factors affecting balance and stability: height of the COG above base of support

the line of gravity or pull of gravity will always pass vertically through the centre of an objects mass

- higher centre of gravity above base of support, less stable the object is

Factors affecting balance and stability: position of line of gravity relative to base of support

line of gravity is an imaginary vertical line passing downwards through centre of gravity. The clearer the line of centre of gravity it is to the limits of the base of support, the less the degree of stability of object.

- Movement is easier when the line of gravity falls outside the objects base of support

Factors affecting balance and stability: extra

- Increasing the size of base of support in the direction of oncoming force

- Horizontally positioning the COG near the edge of the base of support on side of external support.

Centre of gravity, stability + balance

In many sports skills, players are required to unbalance quickly to have fast movement time. This can be done by either:

1. Decreasing size of effective base

2. Displacing the centre of weight quickly outside the effective base (move line of gravity close to base of support)

- EG. When receiving serve in tennis player must be prepared to move quickly in a sideways direction. In order to respond to a wider serve the player sways from side to side keeping centre of weight in motion across base of support. With centre of weight in motion less effort is required to unbalance the player when decision to move direction is made. At last moment players will be seen to bring feet closer together thereby decrease size of effective base and facilitating and unbalancing effort.

sports requiring low stability

Sprint starts, Tennis serve, any aspect of sport requiring quick lateral movement or change of direction

Sports requiring high stability

Wrestling, weight lifting, collision sports

Newton's laws: Force production

The concept of force is common to all newton's laws. Force is the pulling or pushing affect of a body on another body that can

- Get objects moving

Stop objects moving

- Change direction of moving object

- Change speed of moving object

- Balance another force to keep object still

+ Force is defined in simple terms as any push or pull acting on a body.

+ Forces are applied when 1 body comes into contact with another

+ A force is required to initiate, slow down or stop movement of an object

+ Measures in newton's

+ Forces may be external

- Gravity

- Friction

- Air resistance

- Water resistance

+ Can also be internal

- Action of muscles and tendons on skeletal system

Newton's first law of motion states that

A body continues in its state of motions or state of rest unless acted upon by a force.

Newton's first law of motion

The size of the force required to change the state of motion of an object depends on the mass of the object. The greater the mass, the greater force needed to move it.

Inertia

amount of resistance to a change in an objects state of motion

- The greater an objects inertia, the greater the force required to initiate its movement or change its state of motion

- Directly proportional to an objects mass

Newton's second law of motion states that

The rate of change of acceleration to a body is proportional to the force applied to it and indirectly proportional to its mass

Newton's second law of motion: force

The greater force applied to an object, the faster the acceleration will be. Acceleration is directly proportional to force applied

FORCE = MASS X ACCELERATION (m/s/s)

Newton's second law of motion: momentum

MOMENTUM = MASS X VELOCITY

- Object can only have momentum if its moving

- Greater objects momentum, the more force needs to be applied to either stop or slow object down

- When two bodies collide, the one with most momentum will be less effected

Newton's second law of motion: conservation of linear motion

principal states total momentum of two objects before and after impact are equal

- momentum of one object is transferred on contact with other objects resulting in no change in total momentum rather transfer of momentum

Newton's second law of motion: impulse

Change in momentum of an object

IMPULSE = FORCE X TIME

Longer the force can be applied to an object and greater size of the force applied, the greater an object impulse

- Impulse is important in impact and collision situations

Newton's third law of motion states that

For every action, there is an equal and opposite reaction

- when two object act upon each other, the forces are opposite in direction and equal in magnitude.

Projectile motion

A projectile is an object propelled into the air or water by an external force

Projectile motion: 2 forces acting upon it

Air resistance

- Important in ski jumping, skydiving

- In discus, javelin, gold, air resistance affects the aerodynamic characteristics of the projectile

Gravity

- Downwards force brings projectile back to ground

Trajectory of a projectile

Path of projectile is referred to as its trajectory

It has two components causing the trajectory of the projectile to curve

- Horizontal

- Vertical

Factors affecting flight of projectile

determined by

- Angle of release

- Height of release

- Speed of release

- Gravity

- Air resistance

- Spin

angle of release

Determine trajectory shape

With all other things held constant also determines:

1. Time object stays in air

2. Horizontal distance object moves

Theoretical optimum angle of release for distance = 450, provided height of release and landing height remain equal and spin and air resistance not present (never happens on earth)

Height of release

Many sports involve projecting ball from given height and ball landing at ground level

Greater height release of projectile, greater horizontal distance, provided all other factors are equal

1. Release height = landing height = 45 0

2. Release height < landing height > 450

3. Release height > landing height < 450

- Athlete must not sacrifice speed for added release height or optimal angle of release, when one is shifted closer to optimum, another moves further away from being optimal.

Velocity at take off

Greater velocity of release, greater distance projectile will carry

- Speed is most important factor for maximizing distance travelled

- Velocity of projectile at instant of release will determine height and length of the trajectory as long as all other factors are hell constant

3 Axes of rotation

1. Medial axis- navel to lower back (cart wheel)

2. Longitudinal axis- head to toe vertically (ice skater spinning)

3. Horizontal axis- hip to hip (diver performing a forward somersault)