fluid mechanics

• Fluid mechanics/dynamics


  The movements of liquids and gases and how forces affect them.
• Drag force


  A force that acts in opposite to motion.
• Surface drag (skin drag)


  Friction between the surface of an object and the fluid environment.
• Form drag (shape drag)


  Impact of the fluid environment on an object.
• Lift force


  Causes a body to move perpendicular to the direction of travel.
• Streamlining


  Shaping the body so it can move quicker through a fluid.
• Angle of attack


  The tilt of a projectile relative to the air flow
• Bernoulli's principle (cyclist helmet)


  Where air molecules exert less pressure the faster they travel and more pressure when they travel slower.
• Aerodynamics


  The flow of air around a projectile that changes the speed and direction of an object.

  Wind in-front- headwind.

  Wind behind- tailwind.
• Hydrodynamics


  The flow of water around a projectile which can influence the speed and direction of the object.
• Air resistance


  It is a frictional force which occurs when air passes over the surface of objects.
• Laminar flow (skip-able)


  When a football (uniform shape) travels through the air layers of airflow passes the ball in smooth symmetrical lines.
• Turbulent flow (skip-able)


  Air travels round an object the air directly in contact with the object is slowed down by surface friction. On fast moving objects the air is unable to keep in contact with the surface breaks away to form fast moving ripples of air.
• factors that increase & decrease drag - the velocity of a moving body

  the greater the velocity of a body through a fluid, the greater the drag force. E.g., a racing car, sprinter or cyclist will experience a greater air resistance in their competition which increases drag. Consequently  in a sport that is very quick it is important to reduce the effects of drag, this is done by streamlining the body as much as possible.
• factors that increase & decrease drag - cross sectional area of a moving body 


  a large cross-sectional area increases drag. In some sports reducing the effects of drag is crucial to ensure success. E.g., in the tour de France the competitors reduce their cross sectional area by crouching low over the handle bars, rather than sitting up right. Similarly, speed skiers reduce the effects of drag by crouching low – allow them to travel faster.
• Factors that increase and decrease drag

  • Shape and characteristics of a moving body
• A more streamlined aerodynamic shape

  Reduces drag
• Sports scientists are regularly trialling drag resistant clothing to achieve 'marginal gains' in speed, to give competitors the edge over their opposition
• Drag resistant clothing

  • Speed skier's helmet that extends to his shoulders
  • Speed skier's special form fitting suit
  • Speed skier's aerodynamic boots
  • Cycling clothing with ridges
  • Cycling aerodynamic helmet with air ducts
• Purpose of drag resistant clothing

  To reduce the effects of drag and increase speed
• Badminton shuttlecock


  • Unusual shape with feathers
  • Light
• Badminton shuttlecock's shape and surface


  Result in a much larger drag force from air resistance
• Larger drag force from air resistance

  Means the shuttlecock loses speed quickly