Post on 23-Dec-2015
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Sports Mechanics Principles
Sports Mechanics Principles
Forces Centre of Gravity Newton’s Laws Impulse Reaction Momentum Acceleration
Linear Motion Curvilinear Motion Projectile Motion Drag Force Lift Force Spin Angular Motion Axes and Planes
Forces 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 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
GravityFrictionAir resistanceGround reaction forcePoint of applicationDirectionResultant action
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 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 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 & BalanceStability and balance will be easier if: The mass is large The base is large The centre of gravity is low The centre of gravity is located over the base Headstand Handstand
Centre of Gravity 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.”
(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.
ImpulseWhen 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 = FtImpulse 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
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
t
Linear Motion
Movement in a straight line of a body or body part. (Translatory motion)
The sprinter runs from A to B.
Curvilinear Motion
Movement along a curved line.
Most jumps are along a curved line.
Projectile Motion
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 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 Lift force is a
force generated perpendicular to fluid flow.
Direction of fluid
flow
Lift force
Types of Spin 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
BACKSPIN
SIDESPIN
Outcome of Spin 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 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
Horizontal (Frontal)
Anterior/Posterior (Sagittal)