Transcript File

Sport
Biomechanics
Understanding how a skill is performed
mechanically is an important stepping
stone to understanding how it can be
learned.
Basic Laws of Biomechanics
 Sir
Isaac Newton developed three laws to
explain the relationship between forces
acting on a body and the motion of the
body.
What is a Force?
 A force
is a push or a pull. Forces are
measured in Newtons. Did you know that
forces only exist when objects interact!
What is a Force?
 A force
gives energy to an object.
Whenever two objects touch, forces are
involved.
What is a Force?
 A force
can cause acceleration, a change
in direction or deceleration. A force is NOT
required to keep an object in motion
 Examples:
-Drag, Friction, Thrust, Gravity, Weight,
Magnestism
Law 1: Law of Inertia

An object at rest will remand at rest unless
acted upon by some external force.

The greater the inertia an object has the
greater the force needed to move it.
Objects at rest remain at rest unless acted on by
a net force.
A lot of inertia!
Very little inertia.
Since the train is so huge, it is
Since the baby carriage is so small, it
difficult to change its speed. In
is very easy to change its speed. A
fact, a large net force is required to small net force is required to change
change its speed.
its speed.
Objects in motion remain in motion in a straight
line (unless acted upon by an outside force).
A lot of inertia!
Very little inertia.
Since the train is so huge, it is
Since the soccer ball is so small, it is
difficult to stop it once it is moving. very easy to stop it once it is moving.
It is difficult to change its speed. In A small force is required to change its
fact, a large net force is required to
speed.
change its speed.
Law 1: Law of Inertia

In what sports would a lot of inertia be to the
athletes advantage?
-Sumo, Scrumming

In what sports would a lot of inertia be to the
athletes disadvantage?
- Sports requiring quick
- change of direction
Inertia & the Golf Swing

How does inertia affect the golf swing?
Club Head
Golf Ball
Law 2: Law of Acceleration

When a force acts upon a mass, the result is
acceleration of that mass.
a.
The greater the force, the great the acceleration.
The smaller the mass, the greater the acceleration.
The mass will accelerate in the direction the force is
applied.
b.
c.
F
(force)
=
m
(mass)
x
a
(acceleration)
Big masses are hard
to accelerate. Big
masses require big
forces to change
speed.
Small masses are
easy to accelerate.
Small masses require
small forces to change
speed
Assume that both steam engines below
apply the same amount of force.
A heavy train has a difficult
time accelerating. Big
masses require big forces to
change speed.
When the same force is
applied to a less massive
train its acceleration is
greater. Small masses
require small forces to
change speed.
Law 2: Law of Acceleration

How can we apply this law of acceleration to the
golf swing?
- The greater the initial force (contracting
muscles), the greater the acceleration of the club
head and the greater acceleration on the golf
ball on contact.
- The greater the force, the further the golf ball
will travel.
Law 3: Action - Reaction Law
 For
every action, there is an equal and
opposite reaction.
 When
we apply a force this is known as an
action force.
 The
object we apply the force to, applies a
force back, this is a reaction force.
Law 3: Action - Reaction Law
 These
two forces always work in pairs,
and are opposite in direction and equal
in size.
The forces here are equal and opposite. Neither
the dog nor its owner pulls with greater force.
They pull with the same force in opposite
directions
The forces will be equal when the truck
crashes into the car.
Since the car is smaller, the car will have a
greater acceleration.
If forces are always equal and opposite, how
can anything move?
Here is a famous problem: A horse is pulling on a
cart, and the cart pulls back with the same amount
of force. If all forces are equal, how can the horse
and cart move?
Answer: The horse moves because the force he
exerts with his hooves is greater than the force of
the wagon pulling him back.
If forces are always equal and opposite,
how can anything move?

What forces act on the cart? The horse pulls it forward,
and there is a backward force from the ground: friction. If
the horses' pull exceeds the friction of the cart, it will
accelerate.
Acceleration will occur if one force pair (push of
ground/push of horse)
is greater than another force pair (friction/pull of cart).
If forces are always equal and opposite,
how can anything move?
Example 2: If the person's friction forces against the
floor are greater than the refrigerator's friction
forces, the fridge will accelerate.
Motion
General Motion
Angular Motion
Types
of
Motion
Curvilinear Motion
Linear Motion
Linear Motion
When all parts of the body move in a
straight parallel lines (same distance
in same time).
Examples
-Dropping a ball
-Sliding in to first base
-Tobogganing down a hill
Curvilinear motion
When all parts of the body move in a
curved path along parallel lines.
Examples
-free fall sky diving
-path of a tennis serve
-flight of golf ball
Angular Motion
Rotation about an axis that can be
either internal or external.
Examples
-swinging around a high bar
-a bicep curl
-a golf swing
General Motion
Linear motion of the body as a result
of angular motion of other parts of
the body.
Examples
- Cycling
- Swimming
- Kayaking
Projectile Motion
Any object released into the
air is termed a projectile.
All projectiles have a flight path and
flight time depending on how they
affected by the variables below.
-Gravity
-Air Resistance
-Angle of Release
-Speed of Release
-Height of Release
-Spin
Gravity
Gravity acts on a body to give it mass.
The greater the mass of an object the
greater the influence of gravity upon it.
What is the effect of gravity on a
projectile?
- It decreases the height a projectile can
attain.
Gravity
Gravity
Air Resistance
Air resistance acts on the horizontal
component of a projectiles path.
Angle of Release
The angle of release of a projectile
determines the flight path.
a. If the angle of release is high, the
projectile has a longer flight time but
decreased distance.
a. If the angle of release is low, the
projectile has less flight time but
increased distance*
*However if the angle is too low, distance is poor.
Angle of Release
How is distance
and height
manipulated in golf
for the best shot?
- Angle of club head.
Speed of Release
Velocity (speed of motion) of release
will determine the size of the flight
path.
Height of Release
The greater the height of release
the greater the distance gained
Spin
There are two main types of spin
1. Top spin- distance is decreased
with topspin.
2. Back spin- distance is increased
with backspin.
Back Spin
A backspin shot creates a region of low pressure
on top of the ball and a region of high pressure
below. As a consequence, the ball floats suddenly
thereby increasing the distance attained.
Topspin
Q. So how does Topspin work?
A. A topspin shot creates a region of
high pressure on top of the ball and
a region of low pressure below. As a
consequence, the ball dips suddenly
thereby decreasing the distance
attained
A golf ball acquires spin when it is hit. Backspin is imparted for
almost every shot due to the golf club's loft (i.e., angle between the
clubface and a vertical plane). A spinning ball deforms the flow of air
around it similar to an airplane wing; a back-spinning ball therefore
experiences an upward force which makes it fly higher and longer
than a ball without spin.
The amount of backspin also influences the behavior of a ball when it
impacts the ground. A ball with little backspin will usually roll out for
a few yards/meters while a ball with more backspin may not roll at all,
even backwards. Sidespin occurs when the clubface is not aligned
perpendicularly to the plane of swing. Sidespin makes the ball curve
left or right: a curve to the left is a draw, and to the right a fade (for
right-handed players).
Accomplished golfers purposely use sidespin to steer their ball
around obstacles or towards the safe side of fairways and greens.
But because it's sometimes difficult to control or predict the amount
of sidespin, balls may take an undesirable trajectory, such as hook to
the left, or slice to the right (for right-handed players).
Stability
&
Balance
Centre of Gravity
The point in the body about which all
parts of the body are in balance or
the point at which gravity is centred
COG is not confined to one location,
as the body moves so the COG
moves with it in the direction the
movement occurs
RUNNING EXAMPLE
•This runner has an upright trunk
•Level pelvis
•Centre of gravity is well behind the
contact point of the leading foot
•This allow progressive loading of the
leading leg
•With a trunk leaning forwards
•The centre of gravity is almost directly over
the foot as it lands
•The loading on the foot, ankle, knee,
pelvis rises steeply
Increasing Stability
Stability is increased when Centre of
Gravity is lowered
Increasing Stability
Stability is increased when the line of
gravity falls within the BOS (Base of
Support
Increasing Stability
Stability is increased with increased mass
Why?
Greater inertia – requires more force by
an opponent to move the line of gravity
Eg. Rugby – a bigger forward pack has an
advantage in scrums
Increasing Stability
Stability also is increased when BOS
is extended in the direction of an
oncoming force
Stability is increased when the line of
gravity is moved towards an
oncoming force
Biomechanics
of
Torque
(Rotational Force)
Biomechanics of Torque
Rotational movements play an
important part in all sports skills
Rotation can involve:
-the whole body (diving, gymnastics)
-objects (pitching or bowling a ball)
-the body and equipment as levers
(batting, golf)
Axis of Rotation
The axes of rotation of the body act
through the COG
There are 3 axes of rotation
Longitudinal – eg pirouette
Transverse - eg forward roll
Sagittal
- eg cartwheel
Levers
Levers are designed to allow either a
greater resistance to be moved with
a given force
Or to increase the velocity (speed) at
which an object can be moved using
a given force
Parts of a Lever
Levers consist of 3 parts;
a) Resistance
b) Force
c) Fulcrum
The distance from where a force is applied to
the fulcrum is called the force arm (FA)
The distance from where a resistance acts to the
fulcrum is called the resistance arm (RA)
First Class Lever
The fulcrum lies between the resistance and the force
FA shorter than RA favours speed and range of movement
FA longer than RA favours force output
First Class Levers
Second Class Lever
The resistance lies between the pivot and the force
The force arm and the resistance arm are on the same side
of the lever
The FA is always longer than the RA
Second Class Levers
Third Class Lever
The force lies between the resistance and the fulcrum
The FA is shorter than the RA
In third class levers, the force applied is always greater
than the resistance
Third Class Levers
Torque
As all levers produce rotation about an axis, they
also produce torque.
Torque is defined as a turning force
T = F
x
D
Torque = Force x Distance
The greater the force applied to a given force
arm the greater the torque
The longer the force arm with a given force
applied the greater the torque
Initiating Rotation
In order to initiate rotation on any
object, or human body an eccentric
force must be applied
An eccentric force is a force applied
away from the COG
Apply this principle to explain how a
pitching wedge works!
Angular Velocity and
Speed of Rotation
Angular Velocity is the rate of spin of
an athlete or object as they move in
a particular direction
Speed of Rotation is how quickly
parts of an object or athlete move in
a rotational movement
Angular Velocity and Speed
of Rotation
Speed of rotation of an object increases
the further it is away from the axis of
rotation
Speed of rotation of an object increases
the greater the angular velocity
Speed of rotation of an object is a product
of angular velocity and the radius of the
object from the axis of rotation
Force Summation
As we know, in order to generate
momentum a force must be applied
to a body
An athlete is able to achieve a
maximum velocity or force by the
transfer of momentum through
successive body part movements.
Handball
Shot Put
Force Summation
Rule 1: Use All Body Segments
To maximise muscular force we want
to use as many body segments as
possible.
Force Summation
Rule 2: Stretch Out
Before we begin the sequence of
body movements we should stretch
muscles out to their optimal length
to allow muscles to be contracted
with max force.
Force Summation
Rule 3: Sequencing of Body Segments
Generally we move larger muscle groups
first and smaller muscle groups last
Force generated by the larger muscle is
groups passed on to the smaller ones
Force Summation
Rule 4: Timing of Body Segments
To produce max force we need to
ensure that the right body segment
is adding to the overall force at the
right time
If timing is out of order movement
will lack co-ordination and force
generation is lessened or lost
Force Summation
Rule 5: Full Range of Motion
We need to move body segments
through the greatest range of motion
that we can.
Greater the range of motion, the
higher the speed of the extremities
on release/contact