fluid mechanics

Question 1

fluid?

Answer 1

particles move freely, not solid

Question 2

flotation

Answer 2

maintain a stationary position on the surface of the water

Question 3

buoyant force

buoyancy

Answer 3

weight of person acting on the water

force that lifts upwards, against gravity

Question 4

archimedes principle

Answer 4

the buoyant force is equal to the weight of water a person displaces

Question 5

to float

Answer 5

weight must be less than (or equal to)
the maximum buoyant force
OR
the

Question 6

specific gravity

Answer 6

measure of the density of an object

Question 7

positively buoyant

Answer 7

float, body density < water density

Question 8

conditional floaters

Answer 8

float when have inspired air in lungs

Question 9

centre of buoyancy

Answer 9

rotation of axis in water, centre of volume of body displacing the water

Question 10

COB, COG don’t line up

Answer 10

torque will be created, rotation will occur

must be aligned vertically

Question 11

relative motion

Answer 11

e.g. water skiier, water looks like its moving past them
person standing on beach, it looks like the person is moving
can also apply to balls in the air, sidewinds, and wind in general

Question 12

drag force (def)

Answer 12

force exerted by a fluid, reduces speed

Question 13

types of drag

Answer 13

surface
profile or form
wave

Question 14

surface drag

Answer 14

rub against skin
Dependant on-
velocity of flow
surface area

Question 15

profile or form drag

Answer 15

turbulent flow conditions behind object

dependant on shape of the body and the cross sectional area of the body

Question 16

turbulence =

Answer 16

low pressure zone

Question 17

wave drag

Answer 17

interface between two fluids, causes waves
biggest impact on athletes travelling at high speeds
dependant on speed of the swimmer and vertical movement

Question 18

boundary layer

Answer 18

carries fluid on surface

region of relative motion between adjacent particles

Question 19

boundary layer separation

Answer 19

slow speed = laminar or streamline

relative flow increases = separation, turbulence

Question 20

reynolds number

Answer 20

characterises the flow as either laminar or turbulent
dependant on 
velocity
diameter of sphere
density/ viscosity of fluid

Question 21

R > 200,000:

Answer 21

fully turbulent flow (boundary layer)

Question 22

R (approx) 200,000

Answer 22

transition to type III flow

critical layer- boundary layer becomes turbulent, sticks back, decrease the amount of profile drag (around 60%)

Question 23

1

Answer 23

turbulent wake, surface + form drag, type II

Question 24

R < 1

Answer 24

type I, laminar flow, surface drag

Question 25

increasing temp impacts viscosity (how)

Answer 25

gasses, increase

liquids, decrease

Question 26

what happens to the density of air

when you increase, P, temp, humidity

Answer 26

p = increase air density
temp = decreases air density
humidity = decreases air density

Question 27

bernoulli’s principle

Answer 27

flow velocity fast = low pressure

force directed from high to low pressures

Question 28

fluid lift force

Answer 28

acting at right angles to drag

Question 29

angle of attack

Answer 29

main plane of direction and flow direction

Question 30

stall angle

Answer 30

if the angle of attack becomes too large, too much drag

Question 31

angle of release/projection

Answer 31

COG from horizontal, at release

Question 32

angle of attitude

Answer 32

main plane of the object and the ground

Question 33

centre of pressure

Answer 33

the point where the lift and drag (resultant force) act of the object

Question 34

magnus effect

Answer 34

ball moves to low pressure side, faster velocity

depends on the ratio between SRS and the linear speed of the ball

Question 35

SRS (surface rotation speed)

Answer 35

rotation rate x radius of sphere,