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)