fluid mechanics - lesson 10 Flashcards
define fluid flow
The natural science of fluids (liquids and gases) in motion.
what are the 3 fluids forces?
Drag (usually works horizontally)
Lift (usually works vertically)
Bouyancy (works vertically)
what is fluid resistance?
As an object moves through a fluid (air or water), it disturbs it.
- The greater the disturbance to the fluid, the greater the transfer of energy from object to a fluid
what are the two factors affecting fluid resistance?
denisty (air)
viscosity (liquid)
how does density affect fluid resistance?
more dense the fluid = the more disturbed the fluid becomes = greater the resistance
how does viscosity affect fluid resistance?
more viscous the fluid (internal resistance of a fluid to flow) = the more disturbed the fluid becomes = greater the resistance
what is the equation of total drag?
total drag = form drag + wave drag +surface drag
what is surface drag?
the drag created due to a fluid moving over an object resulting in friction between the surface of the body and the fluid
what factors affect surface drag?
- Relative velocity of moving object
- Relative roughness of surface object
- Density/Viscosity of the fluid
- Amount of surface area of the object
what is form drag?
Resistance created by the pressure differential between the front and back of an object moving through a fluid
what factors affect form drag?
- cross sectional area of the object presented to the fluid
- velocity of object > higher speed = greater form drag
- surface roughness
- shape of the object
what drag forces affect cyclists?
SURFACE DRAG and FORM DRAG
how can a cyclist reduce surface drag?
- Wear smooth, tight-fitting clothes (minimize surface area)
- Shave legs
how can cyclists reduce form drag?
- Assume streamlined position = reduce cross-sectional area
- Use Aerodynamic rims
- Aerodynamic helmets (teardrop shape)
- Aerodynamic bike components
define wave drag
the drag created by the body at the interface of two fluids interacting whereby waves are created
what factors affect wave drag?
- Velocity of Wave
- Technique-more streamline will reduce wave drag.
- Open Water v Closed Conditions
how does surface roughness affect surface drag and an example of reducing surface drag?
rougher surface, greater surface drag
swimmers shave and use lotion to reduce surface drag
relationship between the surface area of the object and surface drag
greater surface area, greater surface drag
how does CSA presented to fluid affect form drag?
greater CSA presented to fluid, increases form drag
how does the velocity of the object affect form drag?
at higher speeds, athletes experience greater levels of form drag
how does surface roughness affect form drag?
rougher surfaces, decrease form drag
air clings to the surface for a longer period, causing later separation point
rough surfaces increase surface drag at high velocities
how does the shape of the object affect form drag?
oval ball has less form drag than round ball
swimmers wear tight fitting suits to compress body and produce a more streamliner body shape
how does relative velocity/height of wave affect wave drag?
greater velocity/height of the wave greater wave drag
how do open water v closed conditions affect wave drag?
swimmers in open water are more affected by wave drag from swimmers around them and from seas and swell
lane ropes reduce wave drag by helping dissipate moving surface water
