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Physics > Fluids > Flashcards

Fluids Flashcards

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1
Q

Fluids

A

are able to flow and conform to shapes of their containers; ie: gases, liquids

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2
Q

What is the equation for density?

A

p = m/V

Units: kg/m^3 or g/mL or g/cm^3

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3
Q

What is the density of water?

A

1 g/cm^3 = 1000 kg/m^3

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4
Q

What is the equation for an objects weight when you have density?

A

Fg = pVg

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5
Q

What is the equation for specific gravity and why is it useful?

A

SG = p/ 1 g/cm^3
It is a useful tool for determining if an object will sink or float in water. If the SG > 1, then the object will sink. If the SG < 1, then the object will float

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6
Q

What is the equation for pressure?

A 
P = F/A
P = pressure
F = magnitude of the normal force vector
A = area
Units = Pascal (Pa) = 1 N/m^2, mmHg, torr, atm
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7
Q

What are the conversions between the four units of pressure?

A

1.013 x 10^5 Pa = 760 mmHg = 760 torr = 1 atm

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8
Q

What is absolute/hydrostatic pressure?

A

the total pressure that is exerted on an object that is submerged in a fluid

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9
Q

What is the equation for absolute pressure?

A 
P = P0 + pgz
P = absolute pressure
P0 = incident/ambient pressure (surface pressure)
p = density of fluid
g = a due to gravity
z = depth of the object
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10
Q

What is gauge pressure?

A

the difference between the absolute pressure inside an object and the atmospheric pressure outside

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11
Q

What is the equation for gauge pressure?

A

Pgauge = P - Patm = (P0 +pgz) - Patm
Pgauge =
P = absolute pressure
Unless the surface pressure is equal to atm pressure, then Pgauge = pgz

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12
Q

Hydrostatics

A

the study of fluids at rest and the forces and pressure associated with standing fluids

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13
Q

Pascal’s Principle

A

a pressure applied to an incompressible fluid will be distributed undiminished throughout the entire volume of the fluid

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14
Q

Hydraulic system

A

Operate on pascal’s principle to generate mechanical advantage

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15
Q

What equation would you use for a two piston hydraulic system utilizing pascal’s principle?

A

P = F1/A1 = F2/A2

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16
Q

What is Archimedes’ Principle?

A

states that a body wholly or partially immersed in a fluid will be buoyed upwards by a force equal to the eight of the fluid it displaces

17
Q

What is the equation for buoyacy?

A

Fbouy = pfluidVfluiddisplacedgravity = pfluidVfluidsubmergedgravity

18
Q

What is surface tension?

A

causes the liquid to form a thin but strong layer like a “skin” at the liquid’s surface

19
Q

What is cohesion?

A

the attractive force that a molecule of liquid feels toward other molecules of the same liquid

20
Q

What is adhesion?

A

the attractive force that a molecule of the liquid feels toward the molecules of some other substance

21
Q

Fluid Dynamics

A

study of fluids in motion

22
Q

What is viscosity?

A

the resistance of a fluid to flow (n)

23
Q

What is viscous drag?

A

a nonconservative force that is analogous to air resistance

24
Q

What is the units for viscosity?

A

Pas = (Ns/m^2)

25
Q

What kinds of flow can a fluid have?

A

Laminar flow - smooth and orderly

Turbulent flow - rough and disorderly

26
Q

How do you calculate laminar flow?

A 
Using Poiseuille's Law:
Q = pi*r^4*deltaP/8*m*L
Q = flow rate (volume flowing per time)
r = radius of the tube
deltaP = pressure gradient
n (eta) = viscosity of the fluid 
L = length of pipe
27
Q

What is the relationship between the pressure gradient and the radius of a tube in laminar flow?

A

it is inverse exponential to the fourth power

slight changes in radius have significant effects on the pressure gradient

28
Q

What are eddies?

A

swirls of fluid of varying sizes occurring typically on the downstream side of an obstacle

29
Q

What is critical speed?

A

a speed of flow that if exceeded, the flow turns into turbulent flow. critical speed depends on the physical properties of the fluid and the diameter of the tube

30
Q

What is the boundary layer?

A

a thin layer of fluid adjacent to the wall that is in laminar flow when the rest of the fluid has passed the critical speed in turbulent flow

31
Q

What is the equation for critical speed?

A 
v(subc) = N(subR)*n/pD
v(subc) = critical speed
N(subR) = Reynolds number (will be given)
n = viscosity of fluid
p = density
D = diameter of the tube
32
Q

What are streamlines?

A

indicate pathways followed by tiny fluid elements (some times called fluid particles) as they move

33
Q

Flow rate vs linear speed

A

Flow rate is constant (for a closed system) - volume per time while linear speed changes relative to cross sectional area and is not constant. Linear speed is a measure of the linear displacement of fluid particles in a given amount of time

34
Q

What is the equation for flow rate (aka the continuity equation)?

A

Q = v1/A1 = v2/A2
Q = flow rate
v1 and v2 = linear speeds of the fluid at points 1 and 2
A1 and A2 = cross-sectional areas at these points

35
Q

What is Bernoulli’s equation?

A 
P1 +1/2pv1^2 + pgh1 = P2 +1/2pv2^2 + pgh2
P = absolute pressure of the fluid
p = density of the fluid
v = linear speed
g = gravity
h = height of the fluid above some datum
36
Q

What is energy density and how does it relate to pressure?

A

Energy per cubic meter which is equal to pressure. higher pressures have higher energy densities

37
Q

Venturi flow meter

A

an hourglass shaped tube on it’s side with two tubes sticking straight up, one on one side and another in the middle part. When fluid flows through, it has to increase it’s linear speed in the narrow middle and pressure decreases so the liquid in the vertical tube decreases relative to the other tube

38
Q

What is the Venturi effect?

A

with a lower absolute pressure, the column of fluid sticking up from the venturi tube will be lower at the middle vertical tube than the other vertical tube

Physics (10 decks)

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