Fluid Motion Flashcards
Fluid
A substance that flows when subjected to a shear stress
Primary fluids that affect human movement
- Air
- Water
Relative Velocity
Velocity of a body with respect to the velocity of something else, such as the surrounding fluid
Laminar Flow
Flow characterized by smooth, parallel layers of fluid
Turbulent Flow
Flow characterized by mixing of adjacent fluid layers
Fluid Properties
- Density
- Specific weight
Buoyancy
- A fluid force that always acts vertically upward
- F(b) = V(d)γ
- F(b) = buoyant force
- V(d) = displaced volume
- γ = fluid’s specific weight
Archimedes Principle
The buoyant force acting on a body is equal to the weight of the fluid displaced by the body
Center of Volume
- Point around which a body’s volume is equally distributed
- Point at which the buoyant force acts
Drag Force
- A force caused by the dynamic action of a fluid that acts in the direction of the fluid flow
- F(D) = ½ C(D) ρ A(p) v²
F(D)
Drag force
C(D)
Coefficient of drag
Coefficient of Drag
Unitless number that is an index of a body’s ability to generate fluid resistance
ρ
Fluid density
A(p)
Surface area of the body oriented perpendicular to the fluid flow
v
velocity of the body relative to the fluid
Skin Friction
- Resistance derived from friction between adjacent layers of fluid near a body moving through the fluid
- AKA surface drag or viscous drag
Form Drag
- Resistance created by a pressure differential between the lead and rear sides of a body moving trough a fluid
- AKA profile drag or pressure drag
Wave Drag
Resistance created by the generation of waves at the interface between 2 different fluids, such as air and water
Lift Force
- Force acting on a body in a fluid in a direction perpendicular to the fluid flow
- F(L) = ½C(L)ρA(p)v²
F(L)
Lift force
C(L)
Coefficient of lift
Coefficient of Lift
Unitless number that is an index of a body’s ability to generate lift
ρ
Fluid density
A(p)
Surface area of the body against which lift is generated
v
Velocity of the body relative to the fluid
Foil
Shape capable of generating lift in the presence of a fluid flow
Bernoulli Principle
- An expression of the inverse relationship between relative velocity and relative pressure
- High-velocity areas = low pressure areas
- Low-velocity areas = high pressure areas
Semifoil Shape
Certain projectiles can experience some lift force, but others cannot due to their spherical shape
Angle of Attack
Angle between the longitudinal axis of a body and the direction of the fluid flow
Magnus Force
Lift force created by spin
Magnus Effect
- Deviation in the trajectory of a spinning object toward te direction of spin, resulting from the Magnus force
- Lift force created by spin
Propulsive Drag
Force acting in the direction of a body’s motion
Propulsive Drag Theory
Theory attributing propulsion in swimming to propulsive drag on the swimmer
Propulsive Lift Theory
Theory attributing propulsion in swimming at least partially to lift actin on the swimmer
Stroke Technique
- Swimming speed is the product of stroke length (SL) and stroke rate (SR)
- Focus on increasing force applied to increase SL
