PRESSURE in WATER

• F = force exerted by water against a 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 ] • see FIG D.6 on page 99

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

DENSITYLower than Water Higher than Water

• Air

• Fat

• Bone 50% more dense

• Muscleslightly more dense

ARCHIMEDES Principle• Upward buoyant F

= to volume of displaced water• Floating

- body Wt. Density = to OR < than water WD• Sinking

- body Wt. Density > than water WD

Positive Buoyancy Negative BuoyancyFigure 14.2b Figure 14.2c

• Net Forces 0• water WD than body • body WD than water• body WD due to more

fat tissue

• Net Forces 0• water WD • body WD • body WD due to

less fat, more muscle

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

Fgravity pushes while Fbuoyancy pushes • pitching effect results with rotation @ CB

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

body’s CG• CG and CB are in line

no rotation about CB

Running in Water

• often used in therapy or for adaptive groups• shallow water = buoyancy load on legs• deep water = buoyancy load on legs• Figure 14.4 on page 457• does not seem to transfer training effect to land

running due to SPECIFICITY in Training

RESISTIVE FORCES• 1. Skin Friction

• 2. Profile Drag

• 3. Wave Drag

Skin Friction

• 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

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 streamlining

FIG 14.6 on page 461 and FIG 14.7 on page 462

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 • see FIG 14.8 on page 464• Bow wave in Front Crawl allows breathing with

reduced profile drag