#### Transcript Document

```Sports Mechanics Principles
Sports Mechanics Principles
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Forces
Centre of Gravity
Newton’s Laws
Impulse
Reaction
Momentum
Acceleration
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Linear Motion
Curvilinear Motion
Projectile Motion
Drag Force
Lift Force
Spin
Angular Motion
Axes and Planes
Forces
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Internal forces – produced by the
muscles
External forces – gravity, air resistance
etc.
Forces
“something that causes an object to be
deformed or moved.”
(Roberts & Falkenburg, 1992)
Force can:
 Get objects moving
 Stop objects moving
 Change the direction of a moving object
 Change the speed of a moving object
 Balance another force to keep an object still
External Forces Worksheet
Gravity
Friction
Air resistance
Ground reaction force
Point of application
Direction
Resultant action
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Get objects moving
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Stop objects moving
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Change the direction of a
moving object
Change the speed of a moving
object
Balance another force to keep
an object still
Summation of Joint Forces
In whole body sports skills:
 Using (recruiting) joints in the order, big to
small, will make objects move faster.
(acceleration).
 Using (recruiting) joints in the order, small
to big, will usually result in deceleration.
Locating Centre of Gravity
Single segmental objects have their Centre of
Gravity directly above the base of support.
Sometimes the Centre of Gravity can be found
outside the body. (Arc)
Gravity: A Constant Force
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The Earth’s rotation produces a force
called gravity.
Gravity provides a constant force on
matter, which is commonly understood as
weight.
Weight is mass multiplied by gravity.
Gravity causes objects to travel toward
the earth at a constant rate of
acceleration. 10m/sec2
Human Body Centre of Gravity
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Standing still – centre of gravity is
located in the abdominal cavity, about 6
inches above the pubis symphysis.
As your position changes – so does your
centre of gravity.
The position of the centre of gravity will
determine whether the body is in
balance.
Definition
The centre of gravity is defined as the
point around which a body’s weight is
equally balanced in all directions.
(Hall, 1999)
Centre of Gravity, Stability &
Balance
Stability and balance will be easier if:
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The mass is large
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The base is large
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The centre of gravity is low
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The centre of gravity is located over the base
Handstand
Centre of Gravity
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When the force of gravity acts on a
body, it acts through the centre of
gravity and always moves towards the
centre of the earth.
Symmetrical objects like balls and
cubes have their CoG in the exact
centre of the object.
Objects are 3 dimensional, so the CoG
will be at the point where the axes of
all 3 planes meet.
Inertia - Newton’s First Law
Newton’s first law of motion states that:
“a body will continue in a state of rest or in a
straight line of uniform motion unless
acted on by an external force.”
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(Roberts & Falkenburg, 1992)
Inertia is the resistance of an object to
change.
An object at rest will remain at rest unless
acted upon by a outside force.
Impulse
When a force is applied to an object, the
product of the force (F) and the length
of time (t) that the force is applied, is
called the impulse of the force.
Impulse = Ft
Impulse is equal to Force x time,
measured in Newton Seconds.
Impulse
Depends on:
 The time for which
the force acts
 The size of the force
applied
Reaction -
Newton’s Third Law
Newton’s third law of motion states that:
“for every action there is an equal and
opposite reaction.”
(Roberts & Falkenburg, 1992)
Momentum
Refers to the quantity
or amount of motion
Momentum = Mass x
Velocity
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The runner has a mass of
75 kg and is running at 5
m.s-1.
What momentum does
he have?
375 kg.m.s-1
Acceleration -
Newton’s Second Law
Newton’s second law of motion states that:
“When a force acts on an object, the object
accelerates in the direction in which the force is
acting.”
Acceleration is the rate of change of velocity and
is determined by force.
Acceleration = The final velocity minus the initial
velocity divided by time.
A = v–u
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t
Linear Motion
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Movement in a
straight line of a
body or body part.
(Translatory motion)
The sprinter runs
from A to B.
Curvilinear Motion
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Movement along a
curved line.
Most jumps are
along a curved line.
Projectile Motion
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Motion of an object or person in flight.
Factors Affecting Pathways
The pathway of an object is determined
by:
 The angle of release.
 Drag force is a resistant force
 Lift force
 Type of spin
Drag Force
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Drag force is a resistance force
- a force that slows the motion
of a body through a fluid (air or
water).
Sportsmen reduce drag by
using specialised techniques,
equipment or clothing.
Streamlining reduces form drag.
"Photos courtesy of and copyright Free Range Stock,
www.freerangestock.com"
Lift Force
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Lift force is a force
generated
perpendicular to
fluid flow.
Direction of
fluid flow
Lift force
Types of Spin
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Spin is the rotation of a body or object.
Torque is the force which creates spin.
The type and amount of spin depends on how
much torque is applied and where it is applied.
TOPSPIN
SIDESPIN
BACKSPIN
Outcome of Spin
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Players learn to control the amount of
spin to achieve different effects.
Draw diagrams to represent the
outcome the different types of spin.
Angular Motion
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Sporting activity cannot be defined
purely as linear motion.
Even for the sprinter there is
considerable angular motion.
The legs and arms are rotating about
their particular axis.
Movement Axes
When standing:
 The vertical axis runs from head to foot
through the body’s centre of gravity.
 The frontal axis runs from side to side
through the body’s centre of gravity.
 The sagittal axis runs from front to back
through the body’s centre of gravity.
Movement Axes
There are three axes of movement around
which movement can occur.
 Vertical
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Horizontal
(Frontal)
Anterior/Posterior
(Sagittal)
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