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Biomechanics > Chapter 5 > Flashcards

Chapter 5 Flashcards

1
Q

what is the buoyancy force

A
  • acts in opp direction of gravity
  • dependent on relationship btwn density and volume
  • always acts vertically upward in GRS
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2
Q

based on buotancy when will an object sink/be motionless/float

A

sink: in water when specific gravity is >1
- until wieght of displaced water equals weight of object (will never happen so will settle)
motionless: weight of displaced water equals weight of object
float: in water when specific gravity <1

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3
Q

what is relative velocity?

A

difference btwn the velocities of the two systems

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4
Q

how do you find relative velocity during a head wind

A

add the velocities together

  • or subtract the negative b/c the velocity will be going in opp direction of you
  • fluid going opp direction than object
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5
Q

how do you find relative velocity during a tail wind?

A

subtract velocities

-fluids going in same direction as object

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6
Q

how do you find relative velocity during a perpendicular cross wind

A

cross wind does not effect velocity of the system

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7
Q

how do you find relative velocity during an angled cross wind

A
  • only look at x comp of velocity of wind

- identify if it is a tail or head wind then add or subtract x comp (tail: subtract, head: add)

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8
Q

laminar vs turbulent flow

A

lam: fluid flows smoothly around object and streamlines remain intact
turb: non smoothly flowing fluid and streamlines are broken

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9
Q

what is drag force

equation for drag

A
  • force that acts parallel and in opp direction of object moving
  • =(1/2)(CD)(CSA)(FD)(V2)
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10
Q

break down the equation for drag

A
  • CD: coeffcient of drag; reflects streamlinedness of objects
  • CSA: cross sectional area, surface area in contact w/ fluid flow, perp and para CSA
  • FD: fluid density, increase = increase in drag
  • V: relative velocity, dominant factor in drag force
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11
Q

factors affecting surface drag

4 of them

A
  • smoothness of object
  • parallel CSA of object (sides)
  • density of fluid
  • relative velocity
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12
Q

factors affecting form drag

4 of them

A
  • shape of object msotly the change of shape toward trailing edge
  • perpendicular CSA of object (leading edge)
  • density of fluid
  • relative velocity
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13
Q

what is surface drag

A
  • friction created when streamlines slid over surface of object
  • boundrey layer is slowed
  • nest layer slowed but to lesser extent
  • laminar flow needs to be intact
  • best at slow velocities
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14
Q

what is form drag

A
  • high velocities
  • high pressure zone develops at leading edge
  • low pressure zone devlops at trailing edge
  • pressure gradiant goes opp of motion (from high to low)
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15
Q

what is the lift force?

A
  • perpendicular to oncoming flid flow
  • perpendicular to drag force
  • acts along y axis in local reference system
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16
Q

what is the bernoullis principle

A

fluid pressure inversly related tor fluid velocity

17
Q

what happens to velocity and pressure during pos/neg angle of attack

A
  • pos: HV/LP on top portion and LV/HP on bottom portion

- neg: LV/HP on top portion and HV/LP on bottom portion

18
Q

what is the stall angle

A
  • critical maximum angle of attack

- when lift force suddenly decreases to zero

19
Q

what is the magnus effect

A

lift force on spinning objects

20
Q

what happens to lift force during a top spin on a ball?

A
  • boundrey layers start spinning with ball
  • when boundrey layer is moving in same direction as streamlines HV/LP
  • when boundrey layers are moving in opp direction as streamlines LV/HP
  • ball will fall faster than just gravity acting on it b/c of downwards magnus force
21
Q

what happens to lift force during back spin on a ball?

A
  • same direction = HV/LP
  • opp direction = LV/HP
  • ball will curve upward if looking from side view b/c of upward force
  • ball will curve to the left if looking from top view
22
Q

terminal velocity is affected by…

5 of them

A
  • streamlinedness
  • CSA
  • fluid density
  • relative velocity
  • weight
23
Q

what can sydiver manipulate to have same VERTICAL position as another skydiver

A
  • form drag
  • perpendicular CSA
  • flipped reference system so y axis = x axis in GRS
  • drag force acts in x axis
24
Q

what can a skydiver manipulate to have same HORIZONTALposition as another skydiver

A

lift force

  • flipped reference system so x axis = y axis in GRS
  • lift force acts in y axis
25
Q

what does the streamlinedness of an object depend on

A
  • smoothness
  • shape
  • hoe shape is presented to fluids flow

Biomechanics (15 decks)

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