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biomechanics > chapter 8 > Flashcards

chapter 8 Flashcards

1
Q

when is a fluid force ignored

A

projectile motion

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2
Q

when is a fluid force life-saving

A

skydiving

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3
Q

the force due to immersion in a fluid

A

buoyant force

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4
Q

is a low body fat or high body fat person more likely to float

A

high

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5
Q

magnitude of buoyancy is related to

A

size, how much is immersed

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6
Q

direction of buoyancy

A

always acts vertically upward

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7
Q

buoyant force magnitude equal to ______ displaced by object

A

weight of the volume of fluid

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8
Q

more water displaced=___buoyant force

A

greater

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9
Q

if weight of object >weight of water displaced

A

sink

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10
Q

if weight of object = weight of water displaced

A

float

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11
Q

if weight of object < weight of water displaced

A

rise

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12
Q

ratio of weight of object to weight of the same volume of water

A

specific gravity

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13
Q

if specific gravity <1, object

A

float

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14
Q

if specific gravity > 1, object

A

sinks

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15
Q

ratio of mass and volume

A

density

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16
Q

specific density of bone and muscle

A

> 1, sink

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17
Q

specific density of fat

A

<1, float

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18
Q

Air in lungs decreases

A

specific density of the body

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19
Q

Swimming: weight and buoyant forces not aligned when legs are

A

horizontal

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20
Q

legs sink, weight and torque become

A

colinear, no torque

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21
Q

key to floating

A

weight and buoyant force must align before angular momentum becomes too great

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22
Q

dynamic fluid force present when an object moves ____ or when fluid moves ____

A

within a fluid, past an immersed object

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23
Q

fluid forces directly proportional to

A

density of fluid, square of the relative velocity between body and fluid

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24
Q

fluid density and surface area are __ terms

A

linear

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25
Q

relative velocity is a ___ term

A

squared

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26
Q

double v –> __x dynamic fluid force

A

4

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27
Q

you standing still, wind blowing against you at 5m/s; RV=

A

0-(-5)=5

28
Q

you running at 5m/s, no wind; RV=

A

5-0=5

29
Q

you running at 5m/s, wind blowing against you at 5m/s; RV=

A

5-(-5)=10

30
Q

you running at 5m/s, wind blowing behind you at 5m/s; RV=

A

5-5=0

31
Q

component of the resultant dynamic force that acts on an object in opposition to the relative motion of the object with respect to the fluid

A

drag force

32
Q

what variable is the most impactful in drag force

A

v

33
Q

___affects drag coefficient

A

shape

34
Q

drag forces slow down or speed up an object

A

slow down

35
Q

two ways drag force is produced

A

surface drag, form drag

36
Q

friction between fluid molecules and surface of the object

A

surface drag

37
Q

rougher surfaces create larger ___ forces

A

friction

38
Q

impact forces between the molecules and the object

A

form drag

39
Q

broad, flat leading surfaces of an object create larger __ forces

A

impact

40
Q

if the fluid molecules stay close to the surface of the object at the LEADING surface forms grad force pusing towards the _____

A

rear

41
Q

if the fluid molecules stay close to the surface of the object at the TRAILING surfaceform drag forces pushing towards the

A

front

42
Q

when molecules stay close to the surface

A

laminar flow

43
Q

when molecules separate from the surface

A

turbulent flow

44
Q

how to reduce drag coefficient

A

make body surface, clothing, equipment smooth
streamline the shape of the body and equipment
reduce total SA exposed to flow

45
Q

form drag greater at ___ velocity
surface drag greater at ___ velocity

A

faster
slower

46
Q

how much drag comes from a persons body

A

70%

47
Q

how is drag force beneficial in rowing

A

paddles and oars create drag force to propel the boat or shell

48
Q

how is drag force beneficial in skydiving

A

parachutes use drag force to make landing safe

49
Q

when is drag force beneficial in water exercise

A

rehab and cross-training

50
Q

lift is ___up

A

not always

51
Q

component of the resultant dynamic force on the object acting perpendicular to the relative motion

A

lift force

52
Q

lift force changes direction of ___ of the object in the fluid

A

relative motion

53
Q

lift force can be directed in ___ direction ____ to fluid flow

A

any
perpendicular

54
Q

lift force relation to which of newtons laws

A

3rd law

55
Q

faster moving fluids produce less force laterally than do slower moving fluids

A

bernoullis principle

56
Q

airfoil

A

object with two surfaces aligned with the fluid flow
one surface more curved

57
Q

fluid moves faster over flatter or curved surface

A

curved

58
Q

curved surface=___ fluid =____perpendicular force

A

faster, less

59
Q

flatter surface = __ fluid= ___perpendicular force

A

slower, more

60
Q

lift force is the net effect between

A

unequal perpendicular forces

61
Q

Magnus effect

A

lift force acts on a spinning ball

62
Q

topspin

A

upper surface has forward velocity relative to center of ball
lower surface has backward velocity

63
Q

lift force acts___ on a ball with topspin, acts ___ on a ball with backspin

A

down, up

64
Q

curveball in baseball

A

sidespin creates lift force sideways on a ball

65
Q

dynamic fluid is the resultant of which 2 forces

A

lift and drag

66
Q

center of pressure is the

A

point of application of the force

67
Q

if center of pressure and cg are not aligned

A

torque is created

biomechanics (14 decks)

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