Chapter 11: Fluid Mechanics And Physical Activity

Question 1

• Define fluid dynamics
• What is laminar flow?
• What is turbulent flow?
• Explain what ‘Eddies’ are and how it can be used in paddling.
• Explain what a vortex is
• Explain what wakes are
• Define drag
• How do you reduce the effects of drag?
• The strength of drag depends on what 5 factors?
• What are the 3 types of drag that make up total drag?

Answer 1

• Study of fluids in motion; that is, the way liquids and gases move or flow.
• Flow of a fluid past an object where the fluid flows in continuous lines or layers.
• Random changes in momentum, pressure and velocity characterised by the mixing of adjacent fluid layers.
• Swirls and reverse currents that occur when a liquid/gas flows past an obstruction. Inside an eddy is calm water whereas outer parts are the fast currents. A paddler moving upstream will move from 1 eddy to the next, allowing time to navigate and choose the safest route.
• When fluids are stirred, forming a spinning action around an axis creating a whirlpool effect.
• Represents turbulent flow pattern in the area directly behind an object moving through a fluid.
• The resistance to motion of an object or body moving through a fluid.
• Make the fluid flow as smoothly as possible past the object (increasing laminar flow) rather than stirring it up (decreasing vortices)
  1. Velocity of movement
  2. Frontal cross section of moving body
  3. Size of object
  4. Shape of object
  5. Viscosity of the fluid
• Pressure drag, surface drag, and wave drag.

Question 2

• What is pressure drag?
• What is the boundary layer?
• What is streamlining?
• The magnitude of the surface drag can be affected by what 3 factors?
• What is Bernoulli’s principle?
• Explain the dimples on a golf ball
• What is surface drag?
• What is viscosity?

Answer 2

• Concerns the separation of fluid when a body moves through it. Areas of high pressure are created on the leading surfaces of a body, and low pressure are created on the trailing surfaces. This is known as pressure differential. When the pressure meets again downstream, eddies form creating a slowing effect.
• Immediate layer of fluid near the surface of an object as a fluid moves over it.
• Cross section of the body at right angles to the flow, shape and position of the body and smoothness of surface.
• Making fluid flow smoothly past an object to reduce drag.
• As the speed of a moving fluid increases, the pressure within the fluid decreases.
• The dimples create turbulence in the boundary layer. This ensures the fluid flow remains attached to the surface much further to the back of the ball and for longer, before boundary layer separation. Smaller turbulent wake behind the ball ensures less pressure drag and the ball travels further compared to a smooth ball.
• The friction on the surface of a body as it moves through a fluid.
• fluid’s resistance to flow.