PRESSURE in WATER - PowerPoint PPT Presentation

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PRESSURE in WATER

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Title: BIOMECHANICS APPLICATIONS Author: Robert Vigars Last modified by: rvigars Created Date: 5/24/1997 8:37:16 PM Document presentation format: On-screen Show (4:3) – PowerPoint PPT presentation

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Title: PRESSURE in WATER


1
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

2
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

3
DENSITYLower than Water
Higher than Water
  • Bone
  • Muscle
  • Air
  • Fat

4
ARCHIMEDES Principle
  • Upward buoyant F to volume of ---------
  • Floating- body Wt. Density to OR lt than water
    WD
  • Sinking- body Wt. Density gt than water WD

5
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

6
CB Center of Buoyancy
  • center of the volume of displaced water
  • Force of buoyancy acts at CB
  • CG and CB co-linear gt -----------
  • CG and CB out of line gt ---------- occurs due to
    Fgravity pushes ? while Fbuoyancy pushes ?
  • pitching effect results with rotation _at_ CB

7
Conditional Floater True Floater
  • lungs inflated Floats
  • lungs deflated Sinks
  • Floats with or without inflated lungs
  • fat content ?
  • fat concentrated near bodys CG
  • CG and CB are in line? no rotation about CB

8
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

9
HYDRODYNAMIC RESISTIVE FORCES
  • 1. ------- Drag or ------ Friction
  • 2. -------- Drag
  • 3. ------- Drag (not found in aerodynamics)

10
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

11
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

12
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

13
FIG 14.8 WAVE DRAG
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