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Z 3rd Exam Biomechanics > PowerPoint Chapter 9 > Flashcards

PowerPoint Chapter 9 Flashcards

1
Q

What is fluid mechanics?

A

Fluid mechanicsis the branch of physics concerned with the mechanics of fluids (liquids, gases, and plasmas) and the forces on them.

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2
Q

The most familiar fluid to us is?

A

Water

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3
Q

Hydrostatics?

A

Hydrostatics – Science of water at rest

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4
Q

Hydrodynamics?

A

Hydrodynamics – Science of water in motion

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5
Q

Hydrodynamics has since developed into ____ ____ to incorporate the flow of ____ and other ____ ____?

A

Hydrodynamics has since developed into Fluid dynamics to incorporate the flow of Air and other dynamic fluids

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6
Q

Majority of Fluids are ____?

A

Majority of Fluids are Isotropic

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7
Q

How can fluids be described (3)?

A

Majority of Fluids are Isotropic
Described by defining
-mean mass/unit volume or Density (ρ)
-Temperature (T)
-Velocity (v)

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8
Q

Fluids yield to ____ ____ no matter how small the ____?

A

Fluids yield to Shear stress no matter how small the stress

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9
Q

Pressure to a ____ in a closed container is transmitted without loss to every portion of the ____ and to the ____ of the container?

A

Pressure to a fluid in a closed container is transmitted without loss to every portion of the fluid and to the walls of the container

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10
Q

What is buoyancy?

A

Vertical Supporting Force of a Fluid, upward directed

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11
Q

What is Pascal’s Law?

A

-Pressure at a point in a fluid is equal in all directions
-Ignore horizontal forces; canceled out
-Forces on bottom of object. A higher pressure at the lower portion of an object in water. Pressure difference causes a net force known as Buoyant force

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12
Q

What is Archimedes’ principle?

A

“Any object, wholly or partially immersed in a fluid, is buoyed up by a force equal to the weight of the fluid displaced by the object.”

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13
Q

What is translation (fluid buoyancy)?

A

Translation - an upward force exerted by a fluid opposes the weight of an immersed object

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14
Q

The size of the buoyant force is equal to ____________________________?

A

The size of the buoyant force is equal to the weight of the fluids displaced by the object.

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15
Q

What is positive buoyant?

A

Positive buoyant – object weighs < water displaced. Upward acceleration

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16
Q

What is negative buoyant?

A

Negative buoyant – object weighs > water displaced, Downward acceleration

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17
Q

What is the equation for buoyancy?

A

F(buoy) = rho(f) x V(disp) x g

rho = density of immersing fluid
V = Volume of displace fluid
g = gravity

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18
Q

What is the weight of water?

A

Weight of Water is 9800N/m3

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19
Q

As a scuba dive goes deeper the pressure ____?

A

As a scuba dive goes deeper the pressure increases

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20
Q

What is the science behind a flotation device?

A

Floatation devices
-↑ Buoyancy
-Lowering density
-Hollow construction

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21
Q

Describe the density of the body and different tissues?

A

The Body
-Its density is close to water
-Approx. 70% Water
-Muscle & Bone > Density than H2O
-Body Fat < Density of H2O

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22
Q

What is the center of buoyancy?

A

-The center of gravity of the displaced volume of water, equal in shape and volume of the submerged object it displaced.
-The point where force of buoyancy seems to be concentrated
-Higher than Center of Gravity

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23
Q

Describe dynamic fliud forces (what do they act on)?

A

Acts on a system that is moving through a fluid
The system deflects fluid particles to the outside in order to move through it.

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24
Q

What is dynamic fluid force?

A

Dynamic Fluid Force – The equal and oppositely directed force of the fluid particles in reaction to the applied force of the system moving through the fluid

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25
Q

What are two fluid forces?

A

The 2 Fluid Forces
Drag – parallel
Lift – perpendicular

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26
Q

What is relative motion?

A

Relative motion
-The motion of one object with respect to a reference point
-60mph. Car next lane. Vs Car in opposite lane

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27
Q

What is viscosity?

A

Viscosity
-A measure of the resistance of two adjacent layers of fluid molecules moving relative to each other
Internal friction of a fluid
More viscous fluids move more slowly
Less viscous fluids move more quickly

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28
Q

What is drag?

A

The force resisting motion between object and fluid.
Acts parallel to the flow of fluid by an object but opposite the direction of object motion.

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29
Q

Drag forces tend to ____ ____ the motion of the projectile through fluid?

A

Drag forces tend to slow down the motion of the projectile through fluid.

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30
Q

What effect does fluid density have on drag?

A

Effect of Fluid Density
-As Fluid Density increases so does drag force

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31
Q

What is the formula for drag?

A

F^D = ½ x C^D x p(rho) x A^p x V^2

FD- Drag force
CD- Coefficient of Friction
P- fluid density
Ap- Frontal area of projectile
V2- relative Velocity

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32
Q

What is the coefficient of drag?

A

Unitless quantity that expresses the capability of an object to create drag

33
Q

What does the coefficient of drag depend on?

A

Depends on:
-Shape of object
-Texture
-Orientation relative to fluid flow

34
Q

Higher Coefficient of drag = _______________________?

A

Higher Coefficient of drag = greater ability to generate drag force

35
Q

What are the two kinds of drag forces?

A

Surface Drag
Form Drag

36
Q

What is a boundary layer?

A

Boundary layer: the layer of fluid in immediate contact with the system in motion through a fluid

37
Q

What is laminar flow?

A

Laminar flow: fluid flow in which the molecules of fluid in the boundary layer follow the same smooth unbroken path completely around the object

38
Q

What is streamline?

A

Streamline: the path followed by the molecules of a layer of fluid

39
Q

What is fluid friction?

A

Fluid Friction
-Friction between fluid molecules and the surfaces of the object

40
Q

What are two names for fluid friction?

A

Known as skin friction or viscous drag

41
Q

Use a surfer to explain surface drag?

A

Best Example…….. The surfer
-The board creates a Boundary layer
-Layer of fluid in contact with the object as its moving through.
-Fluid closer to the board moves slower than the rest of the ocean water bc of surface drag
-The change in flow gets smaller and smaller with each successive layer until no friction is is present in outermost layers
-Waxing the surf board to ↓ friction of water and surface drag.

42
Q

What is surface drag affected by?

A

Surface Drag affected by:
Coefficient of Drag, Density of Fluid, Projected area, relative velocity

43
Q

What is form drag?

A

Resistance force to fluid flow created by a pressure differential when fluid flows around a submerged object.

44
Q

What are other names for form drag?

A

Also known as Pressure Drag, Shape Drag, Eddy Drag

45
Q

What is the largest fluid resistance in many sports?

A

Form drag

46
Q

How is form drag created?

A

Collision of the object and molecules of fluid create:
High pressure on the front of the object
Low pressure in the wake of the object.

(Resistance does occur with increased pressure
Bullet in water concept. Loses velocity quickly)

47
Q

What are the two different types of flows?

A

Laminar flow
Turbulent flow

48
Q

Laminar flow?

A

Low velocity conditions, streamlined objects, mostly undisturbed parallel layers

49
Q

Turbulent flow?

A

Fluid molecules bounce off object and each other mixing in chaos

50
Q

What is a water eddy?

A

Noticeable disruption in streamline resulting in Turbulent water flow.

51
Q

Transition between ____ and ____ is not distinct?

A

Transition between laminar and turbulent is not distinct

52
Q

For a sphere. The ____ ____ ____ can change and dramatically effect the response of the ball during a game?

A

For a sphere. The coefficient of drag can change and dramatically effect the response of the ball during a game.

(Ex. Baseball/ softball pitching, Golf ball, Basketball, Volleyball, Tennis)

53
Q

What are two ways to decrease drag pressure for humans?

A

Decrease Frontal area
Streamline

54
Q

What is form drag affected by?

A

Affected by:
-Coefficient of Drag
-Texture of object surface
-Density of fluid
-Projected area
-Relative velocity

55
Q

Drag increases when shape leads to ____ ____ ____ behind the moving object?

A

Drag increases when shape leads to low pressure zone behind the moving object

56
Q

What is wave drag?

A

A disturbance will create waves within the fluids that resist the motion of an object with area projecting at this surface.

57
Q

Why do objects not fall at the same rate?

A

Drag force

58
Q

What is terminal velocity?

A

The velocity at which drag force is equal to the weight of the falling object, and the object will no longer accelerate

Drag force = weight of object, no net force exists

59
Q

Describe the similarities and differences during freefall of 2 objects with the same shape and volume but 1 has a greater mass?

A

-Same drag force
-Different terminal velocities
-The more massive object needs more time to achieve deceleration

(Hail vs Rain drops)

60
Q

What is lift?

A

Fluid force acting perpendicular (90degrees) to the flow of fluid

61
Q

What does lift do in a system?

A

Lift tends to change the direction of the system in motion

62
Q

What does lift depend on?

A

Shape, Velocity, Rotation of object

63
Q

How does an airplane wing work?

A

Airplane Wing
-The key to lift is that wings cause air to be moved vertically downward.
-In other words, wings bend or deflect the paths of the streamlines.
Pulling the air downward lowers the pressure above the wing.

64
Q

Lift doesn’t always go up. It can go ____.
____ lift ____ an object?

A

Lift doesn’t always go up. It can go down
Downward lift stabilizes an object

65
Q

What are two ways (principles/laws) to explain lift?

A

Newton’s Laws
Bernoulli’s principle

66
Q

What is Bernoulli’s principle?

A

The pressure in a fluid is inversely proportional to the velocity of the fluid.
The faster the fluid flow : the lower the pressure the fluid will exert

67
Q

What is the equation for lift force?

A

FL = 1/2 x C(L) x (rho) x A (p) x v^2

FL = lift force
CL = coefficient of lift
 (rho)= density of the fluid through which the object is moving
Ap= projected area of the object (area oriented perpendicular)
v2 = relative velocity of the object with respect to fluid flow

68
Q

What is a foil?
(key to a foil)
(what ratio is key)

A

Any object that can generate lift while moving through a fluid
-Key: Angle of Attack is the optimal angle that maximizes lift and minimized drag
-Lift/drag ratio
-Too Steep? Lift no longer possible bc Drag > Lift this = Stall angle

69
Q

What is the Magnus effect?

A

Lift forces created by the spin of a sphere

70
Q

Size of Magnus force depends mostly on ____ and ____ ____?

A

Size of Magnus force depends mostly on spin and ball roughness

71
Q

What principle is closely correlated to the Magnus effect?

A

Bernoulli’s principle stating that a fluid moving with a high flow velocity exerts less pressure than a fluid moving with low flow velocity

72
Q

Why does the Magnus affect work?

A

Spin causes 2 phenomena
-Pressure gradient on one side of the spinning object to the other side.
-The boundary layer clings to the one side longer than other allowing for fluid particles to be deflected or accelerated.

73
Q

Equal and opposite ____ ____ causes a gradual curve of the path?

A

Equal and opposite reaction force causes a gradual curve of the path.

74
Q

Topspin creates a ____ ____?

A

Topspin creates a downward curve
(Downward lift force)

75
Q

A knuckle ball causes ____ ____?

A

A knuckle ball causes no spin.
(Unpredictable trajectory)

76
Q

What is the principle of spin?

A

Using Spin on a projectile to obtain an advantageous trajectory or bounce

77
Q

Clearly- ____ ____ affect the motion of objects through a fluid?

A

Clearly- fluid forces affect the motion of objects through a fluid.

78
Q

More ____ typically means a lower speed of projectile?

A

More spin typically means a lower speed of projectile

79
Q

How does newton’s laws of conservation of angular momentum affect spin and coaching?

A

If you didn’t get the right spin. The mechanics are wrong. Coaching Cue.

Z 3rd Exam Biomechanics (4 decks)

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