Biomechanics Introduction

Planes of motion& Axes of rotation

LEVERS

The function of a lever in the body is either: To overcome a force greater than the effort used eg

a crowbar / a calf raise To move something a greater distance eg an

overarm throw

A lever consists of: A fulcrum or pivot point – a joint Load – could be gravity, body weight, added weight e.g. gym equipment Effort – provided by muscular contractions

THE LEVERS IN THE BODY ARE THE BONES OF THE SKELETON –

LEVERS CAN BE ADDED IN THE FORM OF SPORTING IMPLEMENTSRACKETSCLUBSBATS

Sporting levers

•Golf clubs are selected according to length – a longer club will produce a longer lever and will send the ball further

•A defender in hockey will use a heavier stick

•An overarm serves in tennis makes the most use of the power by making the lever as long as possible

•A cricketer hitting for 6 will play the shot to make the most of a long lever produced by his body, arms and the bat.

LEVERSREMEMBER- FLE

The part of the lever that is located in the

middle

First Order Lever The fulcrum is in the middle The load is at one end and

the effort applied at the other

Example in the body = Joint at the neck

Second Order Lever

The Load is in the middle The fulcrum is at one end,

the effort applied at the other

Example in the body = The ankle joint

Third Order Lever

The effort is in the middle The load is at one end, the fulcrum at

the other

Example in the body = most of our skeletal muscles

FORCES Before looking at sport & movement, we must understand

FORCE

A force is a push or pull that alters or tends to alter the state of motion of a body

A Force can cause a body at rest to move – (taking a football penalty- the force applied with the foot make the ball move)

A force can cause a moving body to: Change direction – (returning a tennis shot) Accelerate – (a sprint finish) Decelerate – slowing down at the bottom of the ski slope) Change an object’s shape – (jumping on a trampoline)

If a force is applied through the middle of an object – it causes LINEAR MOTION

If a force is applied off-centre it will cause spin or ANGULAR MOTION

Many sporting examples are a combination of both angular and linear motion:

•The upper body shows “LINEAR MOTION”

•Whilst the legs show “ANGULAR MOTION”

This combination is called “GENERAL MOTION”

•Internal forces are generally produced by concentric muscle contraction

•External forces could be:

•Gravity

•Air resistance (water resistance)

•Friction

•Reaction

NEWTON’S LAWS OF MOTION

“A body continues in a state of rest or of uniform velocity unless acted upon by an external force” Law of inertia

NEWTON’S FIRST LAW

NEWTON’S SECOND LAW

“When a force acts on an object, the rate of change of momentum experienced by the object is proportional to the size of the force and takes place in the direction in which the force acts” – Law of acceleration

NEWTON’S THIRD LAW

“For every action there is an equal and opposite reaction” - reaction

Consider: An ice hockey puck is hit by a player & travels across the ice to rebound from the far wall of the rink.

Assume that the friction between the puck & the ice & the air resistance are negligible, & that the puck travels from R to L

Use Newton’s Laws of motion to explain what is happening in the following situations:

1.While the puck is stationary before being hit

2.While the stick is in contact with the puck

3.While the puck is travelling across the ice before it hits the wall

4.While the puck is in contact with the wall

TASK:Write a short piece to apply what you know from today’s lesson to your selected sport

Can you explain how forces are functioning to:

•Cause something to move

•Change direction

•Accelerate

•Decelerate

•Change the shape of an object

Selected sport: trampolining

•Forces acting - pull of gravity makes the performer return to the trampoline – force of the performers muscles changes the shape of the trampoline bed – the force of the trampoline against the performer will cause them to change direction

•Application of Newton’s Laws - External force of performers muscles causes movement (1st Law of acceleration) – The greater the distortion of the bed, the greater the force acting to push the performer upward – they will therefore go higher (2nd Law of acceleration) – The action of landing on the bed causes the reaction of sending the performer upward (3rd Law of reaction)

Centre of Gravity / Centre of Mass

“The point at which the body is balanced in all

directions”

Centre of Gravity & stability The lower the centre of gravity is – the more

stable the position

Base of support

The larger the base of support – the more stable the position

Line of GravityAn imaginary line straight down from

the centre of gravity / mass•If the line of gravity is at the centre of the base of support – the position is more stable

•If the line of gravity is near the edge of the base of support – the position is less stable

•If the line of gravity is outside the base of support – the position is unstable

To work out the centre of gravity of a 2D shape-

Hang the shape from one point & drop a weighted string from any point on the object

Mark the line where the string drops Repeat this by hanging the object from

another point Mark the line again where the string drops The centre of gravity is where the two lines

cross

Jessica Ennis – London 2012