PRESSURE in WATER

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PRESSURE in WATER

• F force exerted by water against submersed body
  
• A area of that body over which F is applied
• water pressure mass of water above body
• pressure ? with depth weight of the water ?
• FIG D.6 on page 99

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WD Weight Density of Water

• Wt. Density (WD) weight per unit volume
• Salt Water has more wt. density than fresh water
  due to salt giving more mass to the water
• Water is NOT compressible / Air IS compressible
• density of water does not change with depth
• air density does change as follows? altitude,
  ? temperature ? density of air

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DENSITYLower than Water
Higher than Water

• Bone 50 more dense
• Muscleslightly more dense

• Air
• Fat

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ARCHIMEDES Principle

• Upward buoyant F to volume of displaced water
• Floating- body Wt. Density to OR lt than water
  WD
• Sinking- body Wt. Density gt than water WD

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FIG 14.2c Negative Buoyancy
FIG 14.2b Positive Buoyancy
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Positive Buoyancy Negative
BuoyancyFigure 14.2b Figure 14.2c

• Net Forces ? 0
• water WD ?
• body WD ?
• body WD ? due toless fat, more muscle

• Net Forces ? 0
• water WD ? than body
• body WD ? than water
• body WD ? due to more fat tissue

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CB Center of Buoyancy

• center of the volume of displaced water
• Force of buoyancy acts at CB
• CG and CB co-linear Float
• CG and CB out of line rotation occurs due to
  Fgravity pushes ? while Fbuoyancy pushes ?
• pitching effect results with rotation _at_ CB

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Conditional Floater True Floater

• lungs inflated Floats
• lungs deflated Sinks
• when drown-proofing
• 1. Exhale then Inhale
• 2. Long hold of air
• 3. CG close to CB

• Floats with or without inflated lungs
• fat content ?
• fat concentrated near bodys CG
• CG and CB are in line? no rotation about CB

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RUNNING IN WATER
a) feet on floor
b) feet do not contact floor
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Running in Water

• often used in therapy or for adaptive groups
• shallow water ? buoyancy ?? load on legs
• deep water ? buoyancy ? ? load on legs
• does not seem to transfer training effect to land
  running due to SPECIFICITY in Training

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HYDRODYNAMIC RESISTIVE FORCES

• 1. Skin Friction
• 2. Profile Drag
• 3. Wave Drag (not found in aerodynamics)

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Skin Friction

• aka Surface Drag
• caused by water moving past surface of body
• ? body surface roughness , ? with water viscosity
  
• ? with smooth surface, tight skin
• least significant Drag Force in swimming

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Profile Drag (aka Form Drag)

• Caused by body front edge pushing water apart
• ? size of front area ? Drag, ?speed ? Drag
  
• Water flow slowed in front ? ? pressure zone
• Water speeds up in back ? ? pressure zone
• Drag ? with streamliningFIG 14.6 on page 461 and
  FIG 14.7 on page 462

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Wave Drag ( Dwave )

• Bow waves act against forward moving body
• caused by moving through or near water surface
• Dwave? with speed of body moving in water
• Dwave? with up and down motions of the body
• Bow wave in Front Crawl allows breathing with
  reduced profile drag

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FIG 14.8 WAVE DRAG