Biomechanical Movement: Fluid Mechanics

Question 1

What is fluid mechanics?

Answer 1

• The study of an object or human body that travels through liquid or gas
• E.g. Swimmers travel through liquid, dicus travels through gas
• Both of these are slowed by friction/drag

Question 2

What are dynamic fluid forces?

Answer 2

• Concerned with the movement of liquid and gases
• Drag and lift are dynamic fluid forces
• Cycling, swimming, sprinting (drag)
• Discus, javelin (drag and lift)

Question 3

What is drag?

Answer 3

• A force that will slow something down
• Can be a resistance force
• Caused by a body travelling through a fluid
• Acts in opposite direction of motion
• Has a negative effect on velocity

Question 4

What is surface drag?

Answer 4

• Friction between the surface of an object and the fluid environment.
• Example: Swimmers -
  …they wear specialised smooth suits, caps and shave body hair; this makes them smooth
  …suits also squash fleshy areas, more streamlined
• This reduces surface drag and increases velocity.

Question 5

What is form drag?

Answer 5

• Refers to the impact of the fluid environemnt on an object.
• Forces affecting the leading edge of an object increases form drag.
• Forces affecting the trailing edge of an object reduces form drag.
• Example: Cyclists -
  …form drag relates to streamlining
  …a large form drag offers less turbulent air for anything following
  …cyclists will use other riders slipstreams.
  …air passes around the first rider
  …form drag is reduced for the second rider meaning they require less energy

Question 6

What is streamlining?

Answer 6

• Shaping a bodu so it can move through fluid efefctively and quickly
• Streamlined body’s incorporate a ‘gradual taper’
• The streamlied shape allows air to move past in layers
• Enables air to flow smoothly
• Reduces fluid drag

Question 7

What is laminar flow?

Answer 7

• Layers of fluid flow slide smoothly over one another
• They undertake smooth paths or layers
• Less resistant to movement

Question 7

What is turbulent flow?

Answer 7

• Flow in which the fluid undergoes irregular fluctuations or mixing constantly undergoing changes in magnitude and directions
• It increases friction and fluid drag and decreases velocity

Question 8

Reducing form drag in cycling?

Answer 8

• As the wind hits the front cyclist, air goes around the sides.
• The cyclist behind uses the ‘air pocket’ created
• Needs to be close: 15-30cm
• Can save 30% more energy

Question 9

What are the factors that reduce and increase drag?

Answer 9

• Velocity of the moving body
• Frontal cross sectional area
• Shape/surface of moving body

Question 10

The velocity of the moving body.

Answer 10

• The greater the velocity of a body through a fluid, the greater the drag force
• In sports that are very quick, its important to reduce the effects of drag
• This is done by streamlining as much as possible

Question 11

Example: Velodrome cycling

Answer 11

• Helmet is designed to encourage laminar flow
• Bike is light weight carbon fibre frame, aerodynamic features
• Body position: head over the bars, low over front wheel, arms tucked
• Clothing: compressed. Skin suit, specially designed tyres which reduces turbulent flow

Question 12

The Cross Sectional Area of the moving body.

Answer 12

• The CSA of a moving body can reduce or increase drag
• A large CSA will increase drag
• In some sports reducing effects od drag is essential for success

Question 13

The Shape/Surface of moving body.

Answer 13

• A more streamlined, aerodynamic shape reduces drag
• Sports scientists are regularly trailing drag resistant clothing
• This helps competitiors with ‘marginal gains’

Question 14

Example: Badminton

Answer 14

• Shape and surface of a shuttle cock results in:
• Much larger drag force from air resistance
• The shuttle is unusual in its shape with feathers
• It’s also very light
• Due to a large drag force, it loses speed quickly