Biomechanics and Skilled Performance

M O T I O N: P R O J E C T I L E , L I N E A R , R O TAT I O N A L & C O M B I N AT I O N

S P E E D & V E L O C I T Y

S U M M AT I O N O F F O R C E , D I R E C T I O N & I M PA C T

L E V E R A G E

N E W T O N ’ S L AW S O F M O T I O N

C E N T R E O F M A S S : B A L A N C E A N D S TA B I L I T Y

E Q U I L I B R I U M , S TAT I C & D Y N A M I C

I M P R O V E D T E C H N O L O G Y & P E R F O R M A N C E

Biomechanics and Skilled Performance

Motion: Linear, Rotational, & Combination

Linear Motion All points in a body travel over the same distance at the

same time in a straight line.Rotational (or Angular) Motion

When the body moves around an axis. Internal axis example:

joint External axis example:

A gymnastic barCombination (or General) Motion

A combination of linear and angular motion. Example: Riding a bike Paddling a kayak

Motion: Projectile

Projectile Motion Any object that moves through the air after being released

can be considered a projectile.A projectile always follows a predetermined path

determined by the angle of release.Gravity and air resistance also affect this

predetermined path.The larger the object the greater the surface

area the more it will be affected be air resistance.

The larger the mass of an object the less it will be affected by air resistance.

Motion: Projectile

Projectile motion is affected by:Angle of Release

The optimum angle of release is 45 degrees. Each sport has its own optimal angle of release based on height and

speed of release.Speed or Velocity of Release

An increase in speed at release point results in a larger horizontal distance.

Height of Release A shot put is released from above 1.5m – Because it already has

some vertical distance more emphasis can be placed on horizontal distance. Angle of release is therefore slightly less than 45 degrees.

When the release point is lower than the landing point the angle of release must be greater than 45 degrees, example: basketball shot.

Speed & Velocity

Speed Distance divided by time.

Velocity Is the speed of an object plus a direction (straight

line) Displacement divided by time Displacement is the change in position a body makes

(m).

Summation of Force

Summation of Force Involves individual forces that combine to create a larger total

force. Correct technique allows for summation of forces to be maximised.

This produces the greatest force. Poor summation of force reduces the force generated by the body.

(see page 283 of blue book)Example – throwing a cricket ball

Body Segment Mass x Speed =Momentum Total Mo.(kg) (m/sec) (kg/m/sec) (kg/m/sec) Trunk 25 4 100 100 Shoulder 20 5.5 110 210 Upper arm 3 15 45 255 Lower arm 2 30 60 315 Hand 1 90 90 405 total momentum

SPEED INCREASES AS BODY SEGMENT MASS DECREASES

Impact

Impact = Force x duration of the force (impulse) Elasticity & Restitution

How elastic something is determines how quickly it returns to its original shape after force is applied. This relies on the following factors: Playing Surface Composition

The softer the surface the lower the elasticity the harder the more elasticity.

Ball Composition The harder the ball the more rebound energy it possesses i.e quickly

returns to original shape (restitution). Temperature

Greater rebound will result when the ball is heated. A golf ball will bounce further on a 40 degree day than a 5 degree day.

Striking Implement Large amounts of compression results in a loss of energy which is not then

used as rebound energy. An aluminum bat hits further than a foam bat. Speed of Implement

The faster the implement on contact the greater the force generated.

Leverage

Levers are simple machines that make work possible and most times easier.

A lever consists of 3 basic components: Effort (force)

In the body this effort comes from the muscles. Resistance (load or weight)

This may be a body part, hitting implement, ball etc…. Axis (fulcrum or pivot)

In the body the axis point is the joint.

Leverage

First class: Effort (force) Axis ResistanceSecond class: Effort (force) Resistance AxisThird class: Resistance Effort (force) Axis

Levers

Other terms associated with levers Effort Arm

Length of the lever from Axis to the Effort. This can increase or decrease in size affecting the

effectiveness of the lever. Resistance Arm

Length of the lever from Axis to the Resistance. This can increase or decrease in size affecting the

effectiveness of the lever.

Levers

Levers

• A Longer Effort Arm and a Shorter Resistance Arm generates more force. See diagram 8.61.

• A Shorter Effort Arm and Longer Resistance Arm generates more speed. See diagram 8.62.

Most of the levers in our bodies are 3rd class levers. What are they designed to do create more force or more speed?

More speed as the Effort and the Axis are close together. The Effort Arm is considerably shorter than the Resistance Arm.

Short Effort Arm equals more speed.

Long Effort Arm equals more force

Levers

• Increased speed can be generated with a longer lever.

• It is not reasonable to extend a lever too far because it cannot be swung quickly due to weight and length.

• Increasing length and decreasing weight is one way to achieve a longer leaver and speed.

• A lever size can be maintained and have a greater mass therefore generating more force. Speed should not be sacrificed to achieve this.

Newton’s Laws of Motions

Inertia – Newton’s First Law of Motion A body at rest will stay at rest unless acted on by an unbalanced

force. A body in motion will remain in motion unless acted on by an unequal force.

Mass is a measurement of inertia. The amount of inertia an object has depends on its mass.

The greater the mass the greater the force required to change its state of motion, whether at rest or moving.

Implications for sport include: A larger athlete with more inertia will be harder to stop. To generate the same inertia (how hard he/she is to stop) as a larger

athlete a smaller athlete will need more speed.


On earth a rolling or sliding object will eventually slow down and stop. What is generally the force associated with slowing down a rolling or sliding object? Friction

Describe a sporting example which involves Newton’s law of inertia. Sumo wrestling – Sumo’s use this principle. The

bigger the contestant the harder it is to push him outside the ring.


Force and Acceleration – Newton’s Second Law of Motion

The change in speed of an object indicates a change in acceleration.

Kick a football at rest and it begins to move. The force (kick) causes movement and since it was not moving it has now accelerated. Therefore Force causes Acceleration.

Mass also affects acceleration. A heavier object will accelerate slower than a lighter one when the same force is applied.

Acceleration = Force (F)Mass (m)


With specific reference to Newton’s 2nd Law, explain how removing much of the interior of a racing car allows for greater acceleration. Acceleration = force/mass: so if a race car has some of

its mass removed (and the engine remains the same) it will create more acceleration, as there is the same amount of force moving a lighter mass.


Action and Reaction – Newton’s Third Law of Motion Whenever one object exerts a force on a second

object, the second object exerts an equal and opposite force on the first object.

Newton’s 3rd Law Action Reaction• The red arrow is the force produced by the body pushing down on the blocks.

• The yellow arrow is the equal and opposite reaction.

• Diagrams 8.74 and 8.75 demonstrates the importance of the angle of force.

Centre of Mass: Balance and Stability

Centre of Gravity Centre of gravity is a theoretical point through which

gravity acts on an object. An object is balanced when the centre of gravity is

located inside the base of support.

Centre of Gravity Base of support


Why doesn’t this object topple over?Because the centre of gravity is inside the base of support.

Which way would this object fall and why? It would fall to the left because the centre of gravity is outside and to the left of the base of support.


If you had to explain to basketball player how to improve their defensive stance what would they need to do and how would you explain it to them? A wide base of support is important requiring the feet to be spread wide. As well as spreading the feet wide the player needs to bend their knees

this lowers the centre of gravity creating more stability. Distribute weight evenly over the base of support. Put both arms up and

out. Only reaching out with one arm will shift the centre of gravity away from the centre.

Static Equilibrium Occurs when the body is stationary. Held positions in gymnastics are

examples.Dynamic Equilibrium

Running is an example. The process of running involves alternating balancing and unbalancing the body.


Rotating Movement Increases stability – a fast spinning top as opposed to

a slow spinning top.Surface Friction

Can influence stability – running on sand as opposed to running on ice.

Additional Mass Mass influences stability. Hard to unbalance but once

unbalanced hard to re balance.


• Where on these two diagrams would the base of support be and the centre of gravity?

• Is the runner in a stable or unstable position in diagram 8.90? Explain.The runner is in an unstable position because the centre of gravity is well outside the base of support. If they do not continue the running action they would fall over.

The Direction of Force• The direction of force impacts on the centre of an objects gravity.• A table tennis ball for example when hit through the centre of gravity will move forward with no spin.• If the same ball is hit above the centre of graity it creates forward movement with rotational movement or topspin.• Hit below the centre of gravity it will produce forward movement and rotational movement or backspin.

Improved Technology & Performance

Clothing More aerodynamic designs have assisted athletes in

sports like, cycling, skiing, swimming and athletics. Improved thermoregulation enables athletes to

remain cooler during competition. Alternately technology has improved clothing allowing athletes to compete in colder climates such as mountaineering and surfing.

Modern materials allow a greater range of movement. Sporting shoes are now designed specifically for the

sport being played. Shoes can be specific to the type of foot and the playing conditions (surface).


Equipment Design The discovery of different metals or alloys has

improved hitting implements. Aluminum, titanium and graphite.

Lighter but stronger materials enable bigger implements (increasing the sweat spot).

Manipulation of shape (Big Bertha driver), composition (tyre selection in racing) or contours (dimples on a golf ball) can improve a piece of equipment.


Surfaces A move away from traditional surfaces like grass,

concrete, bitumen to synthetic surfaces.

Synthetic grass absorbs more shock than concrete, is more stable under foot than grass, is more consistent in bounce and harder wearing.

In hockey this artificial turf has produced a faster more skillful game.

Tennis is unusual because it is played on variety of surfaces at elite level – clay, grass and hard court / rebound ace.

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Biomechanics and Skilled Performance