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KNSS 201: Biomechanics > Fluid Dynamics > Flashcards

Fluid Dynamics Flashcards

1
Q

Define fluid dynamics.

A

study of the effect of the forces that are created when an object travels through a fluid

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2
Q

What is considered a fluid?

A

gases, vapours, and liquids and fluids (sometimes even grains or fine powders)

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3
Q

The 2 fluids that concern us the most are:

A
  • air

- water

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4
Q

Name 3 forces that concern us in fluid dynamics.

A
  • buoyancy
  • drag
  • lift
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5
Q

What is buoyancy?

A

the tendency of an object to float or rise in a liquid or a gas

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6
Q

What is Archimedes principle?

A

any body in a fluid will experience a buoyant force equal to the weight of the volume of the fluid it displaces

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7
Q

Buoyancy is an indicator of ______.

A

density

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8
Q

Density =

A

mass/volume

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9
Q

What is the centre of buoyancy?

A

the point at which the buoyant forces are said to act

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10
Q

Where is the centre of buoyancy in a homogenous body?

A

same as the centre of mass

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11
Q

Where is the centre of buoyancy in a human body?

A
  • mid-chest
  • superior to CoG
  • determines how a body “sits” in water
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12
Q

…..

A

…..

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13
Q

Name the characteristics of a fluid.

A
  • laminar flow

- turbulent flow

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14
Q

What does laminar flow consist of?

A
  • layered
  • closest layer hugs the surface
  • more movement further out
  • bonds between layers = viscosity
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15
Q

What does turbulent flow consist of?

A

layering breaks down to a significant level

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16
Q

What is drag?

A
  • the opposing force acting on an object travelling through a fluid
  • acts in a direction which is opposite to the propelling force
17
Q

What are the 3 kinds of drag?

A
  • surface or friction drag
  • form or pressure drag
  • wave drag
18
Q

What is surface drag?

A
  • similar to friction in that it is reduced by smoothing the surface on which it acts
  • layer of fluid right next to surface is slowed
19
Q

What are 4 factors that affect surface drag?

A
  • relative velocity of fluid flow
  • surface area of body
  • viscosity of the fluid
  • roughness of the body surface
20
Q

What is form drag?

A
  • affected by the area

- caused by pocket of turbulence behind moving body (the faster the relative motion, the greater the turbulence

21
Q

How does form drag create pressure differential?

A
  • positive at leading surface, negative behind

- force directed from high to low

22
Q

How do golf ball dimples relate to form drag?

A
  • creates layer of turbulent flow
  • this layer is carried with the ball
  • flow of the rest of the fluid is laminar = less pressure differential
23
Q

What is theoretical square law?

A
  • all other factors being equal, friction/form drag increases with the square of the relative velocity of motion
  • except for with wave drag, which increases with the cube of the relative velocity of motion
24
Q

Drag has a greater impact for _____ speed sports such as…

A
  • high speed

- downhill skiing, bobsled, luge

25
Q

What is wave drag?

A
  • “wall” of water created in front
  • builds up high pressure
  • greater the velocity, greater the pressure
  • greater impact on swimmer (increases according to the cube of the velocity)
  • effects only felt in water
26
Q

What is lift?

A
  • right angles to the relative flow
  • different pressures on opposing sides of the object (from high to low)
  • up or down
  • Newton’s 3rd law: reaction forces of fluid against object resulting from object’s force applied to fluid
27
Q

What is Bernoulli’s principle?

A

the total energy in steady flowing fluid system is a constant along the flow path. An increase in the fluid’s speed must therefore be matched by a decrease in its pressure

28
Q

What is the Magnus effect?

A
  • spin on a ball causes the path of the ball to be curved
  • ball curves a certain way because it is deflected from a high pressure to a low pressure
  • curve occurs in direction of spin (low pressure)
  • see diagram
29
Q

Give an example of theoretical square law.

A

cyclist crouching low can create a ten-fold reduction in drag

KNSS 201: Biomechanics (7 decks)

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