Fluids

Question 1

Finding weight of volume of substance

Answer 1

Fg = density•V•g

Question 2

Specific gravity

Answer 2

SG=density/ 1g/cm^3

Unitless number

Question 3

Pressure

Answer 3

P=F/A
Pressure =Force/Area

Unit: Pascal (Pa)
1 Pa=1 N/m^2

1.013 X 10^5 Pa = 1 atm

Scalar quantity

Question 4

Absolute (Hydrostatic) Pressure

Answer 4

P=Po + density•g•z

Po= incident or ambient pressure (pressure at surface)
z=depth of object

Question 5

Gauge Pressure

Answer 5

Difference between the absolute pressure in the atmosphere pressure

P(gauge)= P-P(atm)

P= Po + density•g•z

Question 6

Pascal’s Principle

Answer 6

An incompressible fluid will have an undiminished pressure transmitted to every portion of the fluid and to the walls of the vessel containing the fluid (pg 119)

P=F1/A1=F2/A2
V=A1d2=A2d2

Note: the larger the area, The larger the force, although this force will be exerted through a smaller distance

Question 7

Archimedes principle

Answer 7

And object wholy or partially immersed in a fluid will be buoyed upwards by force equal to the weight of the fluid that it displaces

F(buoy)= denaity(fluid)•V(displaced fluid)•g= density(fluid)•V(submerged)•g

Note: ALWAYS use density of fluid, NOT object

Question 8

Viscosity

Answer 8

The resistance of a fluid to flow

Pascal•s (N•s)/m^2

Question 9

Laminar flow

Answer 9

Smooth and orderly; layers of fluid to flow parallel to each other; determine flow by using

Q= (pi•r^4•Delta P)/ (8nL)

Q=flow rate
n= eta (viscosity of fluid)
L=length of pipe

Question 10

Poiseuille’s law

Answer 10

Q=(pi•r^4•Delta P)/(8nL)

MCAT usually focus on relationship between radius and pressure gradient, which is inverse exponential to the 4th power; a slight change in radius of the tube will have significant effect on pressure

Question 11

Turbulent flow

Answer 11

Rough and disorderly flow of fluid; form eddies (swirls of fluid) around object

Question 12

Critical speed

Answer 12

Dependent upon physical properties of a fluid; once exceeded, fluids demonstrate complex flow patterns, and laminar flow occurs in them layer of the fluid by wall

Vc=Nr•n/density•D

Vc=critical speed
Nr=Reynolds number
n=eta (viscosity)
D=diameter of tube

Question 13

Flow rate

Answer 13

Volume of unit per time; constant and independent of changes in a cross sectional plane of a closed system

Question 14

Linear speed

Answer 14

A measure of the linear displacement of fluid particles in a given amount of time; the product of linear speed and cross-sectional area is equal to the flow rate

Q=v1A1=v2A2

Q=flow rate
v=linear speeds
A=area

Equation is known as continuity equation

Question 15

Bernoulli’s equation

Answer 15

P1 + 1/2density•v1^2 + density•gh1= P2+1/2density•v2^2 + density•gh2

V=linear speed
G=acceleration of gravity
H=height of fluid above some datum

The sum of the static pressure and dynamic pressure will be consistent with in a closed container for an in compressible fluid not experiencing viscous drag

Question 16

Energy density

Answer 16

Energy per cubic meter

If u multiply pressure by meters over meters you get N•m/m^2=J/m^3

Question 17

Static Pressure

Answer 17

Same equation as absolute pressure, but h is used to specify height instead of depth

P=Po + density•g•h

Question 18

Venturi effect

Answer 18

As area decreases, the linear speed increases. Then, as the dynamic pressure increases at the smaller area, the absolute pressure must decrease. With a lower absolute pressure, the fluid sticking up from a tube will be lower than that of a larger area

Question 19

Density

Answer 19

D=mass/volume

Units: kg/m^3. May also see g/mL or g/cm^3

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