Fluid mechanics

• Fluid Friction

  refers to objects moving through fluids, referred to as drag in water, air resistance in air
• Air Resistance

  force that opposes the horizontal motion of an object whilst moving through air.

  Decrease velocity, mostly has no effect, factors;

  -weight

  -speed

  -amount of frontal cross-sectional area

  -smoothness of surface area
• Drag

  -Resists/opposes motion of object through air/fluid

  -Dependant on velocity

  -surface drag -> skin friction, roughness of surface increases drag

  -form drag -> air molecules contact object decreases velocity of object, increase cross sectional area, increase form drag.
• Form Drag

  Caused by the shape of the object as it moves through fluid. influenced by the objects cross-sectional area + frontal shape.

  Occurs when the molecules in the air come into contact with the object and its slow velocity

  pressure is high at front, low at back

  creating a pressure differential
• Surface Drag

  "Skin drag"

  Friction between surface and fluid environment

  smoother surface-> less friction -> less resistance

  reduce surface area -> less surface drag
• How swimmers reduce drag

  • Smooth skin suits -> swim caps
  • Shaving -> increase smoothness, allows swimmers to move more efficiently
  • Greater contact with the water, the greater the surface drag due to increase in skin friction
• Laminar Flow

  • Fluid moves smoothly
  • smooth path
  • less resistant to movement/velocity
• Turbulent Flow

  • Irregular fluctuations
  • change in magnitude/direction
  • increase friction
  • decrease velocity