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# Biomechanics Revision 2016

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## Jenny Hall

on 14 September 2016

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#### Transcript of Biomechanics Revision 2016

Conservation of Angular Momentum =

The angular momentum generated at take off remains constant throughout the flight phase of a movement (angular motion) until the athlete lands.

To maximise the movement efficiency during flight, the athlete can only manipulate their
mass and velocity
of rotation.

Remember
– An athletes angular momentum is the product of three components – the athletes rate of spin (i.e.
angular velocity
), the athletes
mass/rotary inertia
and the distribution of the athletes mass (i.e. how extended or tucked the athlete is relative to
the axis of rotation
).

THE BOTTOM LINE IS……………
The flight of the athletes in different sports lasts only a short time. The athletes cannot push or pull against the air to increase or decrease their angular momentum. As a result, the A.M. they give themselves at take off, stays the same (i.e. is constant) for the duration of the flight.

From the Diving Explanation…….

DIVER:

TUCK

LAYOUT
Conservation of Linear Momentum =
Mass x Velocity
=
Mass x Velocity

MOMENTUM STAYS CONSTANT THROUGHOUT

Conservation of Angular Momentum =

TUCK PHASE
Decrease
Rotary Inertia/Mass OR Moment of Inertia x
Increase
Angular Velocity (spin fast) THEN
LAYOUT PHASE
Increase
Rotary Inertia/Mass or Moment of Inertia x
Decrease
Angular Velocity (so you can land safely)

As mass is constant – each aspect is inversely proportional

Momentum is a measure of the amount of motion possessed by that moving body
It is a measure of the force needed to stop or start a motion OR
How hard it is to stop a moving object
Momentum can = motion or movement
Momentum=Mass x Velocity
Remember we need to apply a force to create momentum or movement or change momentum

Momentum

Moment of Inertia or
Rotary Inertia
INERTIA!
The characteristics are resistance and persistence

THEREFORE
Force is needed to produce motion stop movement, or change direction and speed during movement
NEWTONS 1st LAW!

Inertia is resistance to change in motion......

LINEAR

Linear, Curvilinear, Angular or General Motion?

When looking at a skill or movement pattern from a biomechanical perspective, it is often easier to break the skill down into the linear and angular components and analyse them individually.

1.
Linear Motion
involves movement where all parts move in the same direction at the same time along a line or curved line.
2.
Angular Motion
is movement of a body part or object around an axis of rotation.
3.
General Motion
involves translation and rotation at the same time.

Wednesday 21 September 2016,
start 1.40pm-2.40pm
60 minutes, GymC
49 marks - 30% weighting
m/c, short answers and long/extended questions

BIOMECHANICS UNIT TEST FORMAT 2016

Littlewood, K, et al Physical Education VCE Units 1 & 2,Nelson Thomson Learning, 2006, Ch. 4 and 5.
Hosford, G.T, Sports Biomechanics ‘A Handbook for Teachers and Coaches of Sports Skills Victoria, BIPE Publications, 1993.

Bibliography

Is the sequential or simultaneous movement of body parts to produce maximum speed
Begin with the largest and slowest segments and finish with the smallest and fastest segments
It allows full range of movement, maximum summation! (and also increases accuracy)

Summation of Momentum
What segments should be used?
In what order should they act?

Summation of Forces - Rowing

What segments should be used?
In what order should they act?

Summation of Forces - Throwing

FORCE SUMMATION

ROTARY MOTION =
Is the body’s moment of inertia (rotary inertia) x angular velocity
IF YOU

MOMENT OF INERTIA (
INCREASE
THE DISTANCE FROM

THE AXIS OF ROTATION) YOU VELOCITY BUT IF YOU

MOMENT OF INERTIA (
DECREASE
THE DISTANCE FROM THE AXIS

OF ROTATION) YOU VELOCTY

Angular Momentum =

Newtons Third Law explains why momentum is always conserved in any collision

Conservation and Transfer of Momentum

Conservation of Angular Momentum
REACTION

Third Law of Motion (Angular)

For every action there is an equal and opposite reaction.
OR
For every Force there is an equal and opposite Force.

Third Law of Sport!

Torque (angular force) and is the turning effect of a force and is the product of the magnitude (size) of the force, and the length of the force arm (or moment arm or lever).

Torque or Rotary Force - or Moment of Force
Angular acceleration is proportional to the torque (rotary/turning force) acting and takes place in the direction of that torque.
BIG ROTARY FORCE = BIG ROTARY ACCELERATION

Second Law of Motion (Angular) – just substitute Torque (angular/rotary force)
Impulse is Force multiplied by Time.
How is this helpful for athletes?
When athletes apply a greater force over a longer period of time – such as a follow through in a serve or kick or a strike OR cushioning a catch, they can usually either increase the outgoing momentum (and hence velocity of a throw or swing or hit) or decrease the in-coming momentum.
Impulse simply means a change in momentum.
Remember this principle says that force x time gives a change in momentum (m.v)
The bigger range of movement you can use – the bigger impulse you can apply – increase impulse by increasing range of movement
You can create more force over time and the change in momentum (or motion) is bigger as a result!

IMPULSE - a greater range of movement & follow through
There is a relationship between force, mass and acceleration:

F=ma
The heavier an object is, the more force is required for any given amount of acceleration
In objects of constant mass, force is directly proportional to acceleration
Athletes with a smaller mass can accelerate at a faster rate - as acceleration is inversely proportional to force
a = F/m
- so heavier athletes require greater force to accelerate them at the same rate.
This law also relates to momentum, as the momentum of an object is the change in rate of velocity over time (acceleration) multiplied by its mass
Newton’s Second Law of Sport - Acceleration
NEWTONS SECOND LAW
The total force on a body is the mass of the body multiplied by its acceleration
F=ma

If a limb needs to be rotated rapidly, the mid joint (i.e. knee, elbow) should be flexed early and deeply. This gets them accelerating to get them moving!

Flex for Speed

Rotary Inertia and the Limbs
Dependent on the mass of the object and how this mass is distributed relative to the axis of rotation (and the moment arm) - or radius of rotation.
Moment of Inertia
By flexing at the mid joint, the moment of inertia of the limbs can be reduced dramatically, speeding them up and thereby reducing the energy requirements for movements.

Click on the link below to see the race walker in action!
https://goo.gl/images/iFYfwH
Is determined primarily by the mass of the object
It takes a great deal of force to accelerate or decelerate a body
Maintaining constant velocity (or zero velocity - that is not speeding up or slowing down) is more energy efficient at times!

First Law of Motion –
Law of Inertia
The tendency of an object to maintain its state of motion
It is proportional to mass
The greater the mass the greater the inertia!

Its a resistance to change.........

Inertia

Objects like to do what they are currently doing! Unless we apply a force to them!

Newtons First Law of Motion or Sport –
is also called the
Law of Inertia

Is a push or a pull
A blow or an impact
Frictional forces
Force of Gravity
Ground reaction forces
Joint reaction forces
Fluid resistance
Inertial forces
Elastic forces
Magnus effect (of Lift force)
FORCES always act in pairs
It’s a change in velocity - we can speed up, slow down or change direction!
Acceleration is how quickly velocity changes!
Velocity
is speed with direction (distance / time)

Angular Velocity = Rotational Speed

Remember constant velocity is useful for the athlete! Why?
Linear displacement is the distance and direction in which an object moves in a straight line during a given time. The “straight line” distance between the start and finish. Don’t forget we also have angular displacement measured in revolutions.
Distance is the length of the path taken when a body moves from one point to the other.
The actual distance an athlete travels from start to finish.
Distance or Displacement
The father of Calculus, Newton used his outstanding mathematical ability to describe the laws of motion Principia Mathematica Philosophiae Naturalis (published 1668)

Sir Isaac Newton (1642-1727)
The Laws of Motion or Sport!

What segments should be used?
In what order should they act?

Summation of Forces - Kicking

If you’ve got it, use it
Use it in the correct order
Get the timing right
Stabilise it once it has acted (otherwise no transfer)

Summation of Force/Momentum/Velocity –
The Rules!

The following situations represent practical applications of which of Newton’s laws of SPORT?

Newton’s Laws of Sport OR Motion
For every force that is exerted by one body on another there is an equal and opposite force exerted by the second body on the first

Third Law of Motion

The greater the forward lean on take off the greater the angular acceleration.

Newton’s Second Law of Motion – applied to Diving

Is the body’s reluctance to change its angular (rotary) motion
Remember usually relates to an axis of rotation
Think about where the mass is distributed (e.g. is the athlete tucked or extended?)
Remember we come back to this when we discuss angular momentum

A rotating body will continue in a state of constant rotary motion/angular momentum until an external torque (rotary force)
acts upon it.
First Law of Rotary Motion (Angular)
No force = No movement

Gravity

Every body continues in its state of rest or motion in a straight line unless compelled to change that state by external forces exerted upon it.
NEWTONS First Law of SPORT
Mass
is the amount of matter that makes up an object

Weight
is a measure of the force gravity exerts on a body

Therefore we commonly use weight as an indirect measure of mass.
MASS OR WEIGHT?

The rules that govern Exercise Science
Refresher for test and lab!
BIOMECHANICS
Technique Analysis

What segments should be used?
In what order should they act?

Summation of Forces –
Tennis Volley

Elbow

Trunk

Legs

Time

Angular Velocity

In order for the efficient transfer of force in a multi-joint action, each joint must begin to act when the previous joint has reached it’s maximum velocity or force.
The principle of Summation of Forces or Momentum or Velocity
General Motion
THE LAW OF INERTIA
or Rotary Inertia
a heavy racquet is harder to swing!
Big Force = Big Acceleration
Impulse
Starting out..
Motion
Mass/inertia
Distance/Displacement
Velocity & Acceleration
Forces
2nd Law of Sport
The Law of Acceleration
Big Force = Big Acc'n

1st Law of Sport
Inertia & Rotary Inertia
No Force = No Movement

3rd Law of Sport
Law of Reaction
Equal & Opposite Forces

Questions?
Summation of Force & Momentum
Newtons Laws of Sport!
Conservation & Transfer of Momentum & Angular Momentum
ACTION
REACTION
Throwing
Kicking
Striking
In order for the efficient transfer of force in a multi-joint action each joint must begin to act when the previous joint has reached it’s maximum velocity or force.

Newtons Laws of Motion
FORCE & MOTION
An object will always apply a reaction torque proportionate in size but opposite in direction
A rotating body will continue in its state of constant angular momentum (rotation) until an external torque compels it to change its state of motion.
This is also called the law of conservation of angular momentum.
How does Biomechanics enhance sports performance and improve movement efficiency?
Torque (angular/rotary force) is the turning effect of a force and is the product of the magnitude of the force, and the length of the force arm (or moment arm or lever). A greater turning effect (or torque) is usually caused by a longer moment arm.
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