Fluids

Question 1

What is the unit for density?

Answer 1

kg/m^3 ; g/mL ; g/cm^3

Question 2

What is the equation for Density?

Answer 2

ρ = m/V

Question 3

What is the Density of Water?

Answer 3

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

Question 4

What is the equation for Buoyancy force?

Answer 4

Fg = ρVg (unit: N )

Weight of a volume of the given substance

Question 5

What is the equation for Specific gravity and when is it used?

Answer 5

SG = ρ/ (1g/cm^3)
Used to compare the density of a fluid with pure water at 1 atm and 4 degrees Celsius where its ρ = 1 g/cm^3. This will show whether the substance will flow or sink in water.

Question 6

What is the equation for Pressure?

Answer 6

P = F/A

Question 7

What is the SI unit for Pressure? How can the SI unit be converted to mmHg, torr, and atm?

Answer 7

Pascal(Pa). 1.013 x 10^5 Pa = 760 mmHg = 760 torr = 1atm. 1 Pa = 1 N/m^2

Question 8

What is Absolute pressure? What is the typical ambient pressure?

Answer 8

Total pressure on an object.
Ambient pressure + pressure from the fluid if submerged.

P = Po + ρgz
Po: Ambient pressure, pressure at surface
ρ: density of fluid
z: depth of the object

Typically, Po = 1atm

Question 9

What is Gauge pressure?

Answer 9

Difference between Absolute pressure and Atmospheric pressure

P(gauge) = P - P(atm) = (Po + ρgz) - P(atm)

Question 10

What is Pascal’s principle?

Answer 10

If pressure is applied at one point in an incompressible fluid, the pressure if distributed out evenly.

Question 11

What is the equation for Pascal’s principle, comparing the pressure at two different pistons?

Answer 11

Pressure remains the same; P = F1/A1 = F2/A2

Question 12

What is the equation that shows the Volume displaced by piston 1 comparing with piston 2?

Answer 12

Volume remains the same; V1 = A1d1 = A2d2

Question 13

How is work related to pressure and volume changes in two pistons? Show with the equation

Answer 13

W = PV(cos Θ)

= (F1/A1)(A1d1) = F1 x d1 = F2 x d2

Question 14

What is Archimede’s principle?

Answer 14

Law of buoyancy.

F(buo) = ρV(disp)g = ρV(sub)g

Question 15

How is Specific gravity used to find out how much volume of the material has sinked in H2O?

Answer 15

If ice’s ρ = 0.92 g/mL, ice will be submerged 92% of volume, and 8% floating.

Question 16

What is buoyancy force essentially equal to?

Answer 16

weight of the object floating

Question 17

If 70% of an object is submerged in fluid A, then how big will the ρ of the object be compared to fluid A?

Answer 17

70%.

If fluid ρ is 1, then object ρ is 0.7

Question 18

What is Viscosity(η)?

Answer 18

Resistance to flow

Question 19

What is the difference between Laminar and Turbulent Flow?

Answer 19

Laminar flow: smooth and orderly, layers of fluid that flow parallel to each other

Question 20

What is Poiseuille’s law and its equation?

Answer 20

Rate of flow is ^4 proportional to radius, and inversely related to Length of the pipe
Q = (π)(r^4) (ΔP) / 8ηL
Q: flow
ΔP: Pressure gradient
η: Viscosity
L: Length

Question 21

What is Turbulent flow?

Answer 21

rough and disorderly pattern

Question 22

When do we observe turbulence in the flow?

Answer 22

When the speed of fluid exceeds the critical speed

Question 23

What is the formula for critical speed?

Answer 23

v = (N)(η) / ρD
N: Reynold's number
D: Diameter
η: Viscosity
ρ: Density

Question 24

How is Flow rate(Q) related to speed of fluid(v) and cross sectional area(A)?

Answer 24

Q = v1 A1 = v2 A2
v1: speed of fluid at point 1
v2: speed of fluid at point 2
A1: cross sectional area 1
A2: cross sectional area 2
Conservation of Energy = two systems are balanced, so if one increases the other decreases

Question 25

What is Bernoulli’s equation and what does it demonstrate?

Answer 25

P1 + 1/2ρv(1)^2 + ρgh(1) = P2 + 1/2ρv(2)^2 + ρgh(2)
Dynamic pressure + Static pressure will be constant in a closed container at any two points
If Dynamic P increases, Static P decreases, and vice versa.

Question 26

What is Venturi effect? draw a diagram and explain.

Answer 26

Static pressure = P + ρgh
Dynamic pressure = 1/2(ρv^2)
As Static pressure increases, Dynamic pressure decreases, and vice versa.
Static pressure is at a point where Cross sectional area is big
Dynamic pressure is at a point where Cross sectional area is small
High Velocity = Low pressure. Venturi effect.