chapter 8 Flashcards
when is a fluid force ignored
projectile motion
when is a fluid force life-saving
skydiving
the force due to immersion in a fluid
buoyant force
is a low body fat or high body fat person more likely to float
high
magnitude of buoyancy is related to
size, how much is immersed
direction of buoyancy
always acts vertically upward
buoyant force magnitude equal to ______ displaced by object
weight of the volume of fluid
more water displaced=___buoyant force
greater
if weight of object >weight of water displaced
sink
if weight of object = weight of water displaced
float
if weight of object < weight of water displaced
rise
ratio of weight of object to weight of the same volume of water
specific gravity
if specific gravity <1, object
float
if specific gravity > 1, object
sinks
ratio of mass and volume
density
specific density of bone and muscle
> 1, sink
specific density of fat
<1, float
Air in lungs decreases
specific density of the body
Swimming: weight and buoyant forces not aligned when legs are
horizontal
legs sink, weight and torque become
colinear, no torque
key to floating
weight and buoyant force must align before angular momentum becomes too great
dynamic fluid force present when an object moves ____ or when fluid moves ____
within a fluid, past an immersed object
fluid forces directly proportional to
density of fluid, square of the relative velocity between body and fluid
fluid density and surface area are __ terms
linear
relative velocity is a ___ term
squared
double v –> __x dynamic fluid force
4
you standing still, wind blowing against you at 5m/s; RV=
0-(-5)=5
you running at 5m/s, no wind; RV=
5-0=5
you running at 5m/s, wind blowing against you at 5m/s; RV=
5-(-5)=10
you running at 5m/s, wind blowing behind you at 5m/s; RV=
5-5=0
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
drag force
what variable is the most impactful in drag force
v
___affects drag coefficient
shape
drag forces slow down or speed up an object
slow down
two ways drag force is produced
surface drag, form drag
friction between fluid molecules and surface of the object
surface drag
rougher surfaces create larger ___ forces
friction
impact forces between the molecules and the object
form drag
broad, flat leading surfaces of an object create larger __ forces
impact
if the fluid molecules stay close to the surface of the object at the LEADING surface forms grad force pusing towards the _____
rear
if the fluid molecules stay close to the surface of the object at the TRAILING surfaceform drag forces pushing towards the
front
when molecules stay close to the surface
laminar flow
when molecules separate from the surface
turbulent flow
how to reduce drag coefficient
make body surface, clothing, equipment smooth
streamline the shape of the body and equipment
reduce total SA exposed to flow
form drag greater at ___ velocity
surface drag greater at ___ velocity
faster
slower
how much drag comes from a persons body
70%
how is drag force beneficial in rowing
paddles and oars create drag force to propel the boat or shell
how is drag force beneficial in skydiving
parachutes use drag force to make landing safe
when is drag force beneficial in water exercise
rehab and cross-training
lift is ___up
not always
component of the resultant dynamic force on the object acting perpendicular to the relative motion
lift force
lift force changes direction of ___ of the object in the fluid
relative motion
lift force can be directed in ___ direction ____ to fluid flow
any
perpendicular
lift force relation to which of newtons laws
3rd law
faster moving fluids produce less force laterally than do slower moving fluids
bernoullis principle
airfoil
object with two surfaces aligned with the fluid flow
one surface more curved
fluid moves faster over flatter or curved surface
curved
curved surface=___ fluid =____perpendicular force
faster, less
flatter surface = __ fluid= ___perpendicular force
slower, more
lift force is the net effect between
unequal perpendicular forces
Magnus effect
lift force acts on a spinning ball
topspin
upper surface has forward velocity relative to center of ball
lower surface has backward velocity
lift force acts___ on a ball with topspin, acts ___ on a ball with backspin
down, up
curveball in baseball
sidespin creates lift force sideways on a ball
dynamic fluid is the resultant of which 2 forces
lift and drag
center of pressure is the
point of application of the force
if center of pressure and cg are not aligned
torque is created
