Post on 22-Dec-2015
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
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)
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