STA Level 2 Certificate in 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 STABLEUNSTABLE 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 Body Body PartSpecific Gravity Bone1.8 Muscle1.05 Fat0.93 Average Body0.98  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 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 Swimming C.O.G 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 STABLEUNSTABLE 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 1 st 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 2 nd Law of Motion  To increase in speed the force applied needs to increase

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

Application to Swimming Newton’s 1 st Law of Motion  Water slows us down (resistance) Newton’s 2 nd 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 3 rd 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

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 3 rd 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 Water Flow Direction of Hand Movement High Pressure Low Pressure Lift

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