STA Level 2 Certificatein Swimming Teaching

Tutor:

Hydrostatics and Hydrodynamics

Hydrostatics Hydro - meaning - water Static - meaning - not moving

The study of floating and buoyancy

Buoyancy Ability of an object to float in a liquid

Centre of Gravity

Centre of Buoyancy

STABLE UNSTABLE

DIRECTION OF ROTATION

STABLE UNSTABLE

Direction of Rotation

Centre of Gravity

Centre of Buoyancy

Density Is the weight of an object relative to its size? Expressed as mass to volume

Example: Grams per cubic centimetre Fresh water has a density of 1.00 Anything with a density above 1.00 sinks Anything with a density below 1.00 floats

Density: Human BodyBody Part Specific Gravity

Bone 1.8

Muscle 1.05

Fat 0.93

Average Body 0.98

The ability to float depends on body composition.

Human Body Types

Ectomorph Tall, lean with narrow shoulders and hips They have very little body fat

Endomorph Small with wide hips Have a high percentage of body fat

Mesomorph Broad shoulders and narrow powerful hips Classic triangular shaped person

Centre of Gravity / Buoyancy

Gravitational forces act downwards The point at which a suspended object would be

perfectly balanced in all direction

Buoyancy forces act upwards The imaginary point in the centre of the space of the

displaced water made by the object placed in it

Centre of Gravity: Human Body The centre of gravity, which is not a fixed point, lies just

below the naval and is closer to the front of the body When the centre of gravity and the centre of buoyancy

are equal and opposite together the body will remain stable – mushroom float

A shift in direction of centre of gravity and centre of buoyancy will result in the learner rolling

Floating

The ability to float is also influenced by: Centre of gravity – a force that acts downwards Centre of buoyancy – a force that acts upwards

Centre ofGravity

Centre ofBuoyancy

Water

Level

Centre of Gravity

Centre of Buoyancy

Water

Level

Floating Position Float position may be altered moving the limbs when the

body is in the horizontal Float position may be altered by the action of the head in

the vertical

ROTATION

Centre of Gravity

Centre of Buoyancy

Applying this to SwimmingC.O.G

C.O.B

C.O.B

C.O.G

Stable or unstable?

Which way does the learner rotate?

How can we use this information when we teach ?

Stability An object will be stable in the water when its

centre of gravity is vertically lined up with its centre of buoyancy

Centre of Gravity

Centre of Buoyancy

STABLE UNSTABLE

DIRECTION OF ROTATION

STABLE UNSTABLE

Direction of Rotation

Centre of Gravity

Centre of Buoyancy

Relevance to Teaching Learners with a density of greater than 0.98 need to put in

more effort to move in water Keep as much of the body in water when learning to swim The head is the heaviest part of the body Fat floats – Plump learners will struggle to regain feed

when swimming

Relevance to Teaching Explosive breathing most effective method of breathing Buoyant learners might roll when pushing and gliding or

floating Air filled buoyancy aids will make a learner float higher in

the water

Hydrodynamics Hydro – to do with water Dynamics – to do with forces that produce

movement The study of movement, propulsion and resistance Newton’s Laws of Motion

Newton’s Laws

Newton’s 1st Law of Motion Overcoming inertia Every object in a state of uniform motion tends to remain

in that state of motion unless an external force is applied to it

Newton’s 2nd Law of Motion To increase in speed the force applied needs to increase

Newton’s Laws

Newton’s 3rd Law of Motion For every action there is an equal and opposite

reaction

Application to Swimming

Newton’s 1st Law of Motion Water slows us down (resistance)

Newton’s 2nd Law of Motion In order to speed up the rotation of limbs must increase

or the force applied to the water must increase

Newton’s 3rd Law of Motion To move forward the water must be directed backwards

(propulsion in stroke)

Resistance Frontal resistance Surface friction Costume drag Wave drag Eddy drag

Frontal Resistance

Caused by: Incorrect body position

Reducing resistance: Flat body position Correct pathway of arms and legs in the stroke Tilt of the body in front and back crawl Undulation of body in breaststroke and butterfly

Surface Friction

Caused by: The “stickiness” of the water

Reducing resistance: Smooth, shaven skin Close fitting costumes Swimming caps

Free flow

Learner’s body

Costume Drag

Caused by: Loose and ill fitting costumes Long surfer type shorts

Reducing resistance: Close fitting costumes

Wave Drag

Caused by: Energy contained in the wave in a rotating form

Reducing resistance: Correct technique Anti-turbulence lane ropes

Direction of learner

Direction of waves

Eddy Drag

Caused by: Water not joining up quickly behind

learner

Reducing resistance: Streamlined, clean entry and exit Hands angled at entry Toes pointed

Direction of travel

Direction of water

Direction of travel

Direction of water

Paddle Using arms like an oar to grip the water The catch position in all strokes is important to gain

maximum purchase on the water and keep hold of it The action can be alternating or simultaneous This action occurs in all strokes

REACTION

ACTION

Reaction

Action

Finning The up and down movement of the legs either alternately

or simultaneously The downward pressure on the water drives the water

backwards, moving the learner forward Newton’s 3rd Law of Motion For every action there is an equal and opposite reaction

Backward Thrust

Downward Thrust

Resultant Force

Sculling Occurs in all strokes Can be movement of either the arms or the legs Breaststroke legs and treading water displays this

movement best

Sculling Sculling can enable the learner

to remain stationary or it can travel the learner

The force applied by the direction of the palm moves the learner in the opposite direction – Newton’s Law

The arm sculling movement is recognised by the elongated “S” pull

HIGH PRESSUREDIRECTION

OF HANDMOVEMENT

LOW PRESSUREWATER FLOWWater Flow

Direction of Hand Movement

High Pressure

Low Pressure

Lift

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