2.2 Mechanics - Fluid Dynamics (Lvl 2)

Question 1

How is density decribed?

Answer 1

How closely packed particles are in a solid, liquid or gas.

In other words, the amount of mass per unit volume.

Question 2

What is the difference between densities of a material as a solid, liquid and gas?

Answer 2

Solid and liquids have very similar densities due to be tightly packed in both states.
Gas is less dense because the particles are spread further apart which means it has a high volume.

Question 3

What does density depend on?

Answer 3

The type of material.

Question 4

How is density calculated?

Answer 4

Desnity = Mass/ volume (p=m/V)

p = kg/m^3
m = kg
V = m^3.

Question 5

Mass is often in grams, when used to calculate density. How would you provide the answer is kg/m^3?

Answer 5

Multiply by 1,000.

Question 6

What is specific gravity often referred to as?

Answer 6

Relative density.

Question 7

What is the purpose of specific gravity?

Answer 7

Used to compare the densities of two substances and iare compared with water at 4 degrees celcius.

Question 8

What is the formula of specific gravity?

Answer 8

SG = p1/p2

SG = Specific gravity
p1 = p of a liquid or solid OR p of a gas. (kg/m^3)
p2 = p of water OR air (kg/m^3).

or

SG = w1/w2

w1 = Weight of a volume of a liquid or solid OR Gas (kg/m^3)
w2 = Weight of water of equal volume OR air of equal volume (kg/m^3).

Question 9

How are specific gravities measured?

Answer 9

Using a hydrometer.

Question 10

How does a hydrometer work?

Answer 10

A float rises and sinks depending on the density of the liquid.

Float rises when in denser liquid.
Float sinks when is less dense liquid.

Question 11

In Fluid pressure, how is the pressure exerted determined?

Answer 11

By the height of he column and the type of fluid.

Question 12

What does Pascals Law explain?

Answer 12

That when a pressure is applied to a contained liquid, he liquid exerts an equal pressure at right angles to the container that encloses it.

Question 13

What is the formula for Pascals Law?

Answer 13

F = A x P

F = Force produced by a hydraulic piston (N)
A = Area of the piston (m^2)
P = pressure exerted by the fluid (kg/m^3).

Question 14

What could be gained in a hydraulic system by using a piston with a small area to force a fluid into a cylinder with a larger piston?

Answer 14

Mechanical Advantage.

Question 15

What is viscosity?

Answer 15

The resistance of a fluid to change in shape, or to relative movement of neighboring portion within the fluid.

Viscosity denotes opposition to flow and is caused by the internal friction between molecules.

Question 16

What does the viscosity of a fluid determine in spraying, injection molding and surface coating?

Answer 16

The liquid flow.

Question 17

What determines how the air will flow around an aircraft?

Answer 17

1. Viscosity
2. Density.
3. Compressibility
4. Temperature.

Question 18

Why is it important to know the viscosity of fuel at different temperatures?

Answer 18

It has an influence on how well they atomise.

Question 19

Viscosity of liquids changes with temperature, how so?

Answer 19

Decreases rapidly with an increase in temperature.

Question 20

Viscosity of gases changes with temperature, how so?

Answer 20

Increases with an increase in temperature.

Question 21

What factors determines the amount of fluid friction on a solid object?

Answer 21

1. Viscosity
2. Surface texture
3. Shape of the object.

Question 22

What occurs when a solid object travels through a liquid of gas?

Answer 22

Fluid resistance or fluid friction.

Question 23

What is a method of decreasing fluid friction?

Answer 23

Streamlining.

Question 24

What is the standard ISA speed of sound?

Answer 24

340 m/s.

Question 25

At what speeds is the effects of compressibility particularly important?

Answer 25

Supersonic speeds.

Question 26

What happens to air molecules at supersonic speeds?

Answer 26

Becomes increasingly compressed due to the speed of the airflow.

Question 27

If a liquid is compressible, what will cause an increase in the liquid internal temperature?

Answer 27

Increase in pressure.

Question 28

What is total pressure?

Answer 28

The sum of dynamic and static pressure.

Question 29

What is dynamic pressure?

Answer 29

The pressure that emerges from velocity of the fluid in motion.

Question 30

What does Bernoulli’s theorem explain?

Answer 30

The relationship between potential energy and kinetic energy in a fluid.

Question 31

What does Bernoulli’s theorem state?

Answer 31

That when energy is neither added to nor taken away from a fluid in motion, the potential energy, or pressure, decreases when the kinetic energy or velocity increases.

Question 32

In Bernoulli’s theorem, what is the difference between potential energy and kinetic energy?

Answer 32

Potential energy in caused by the fluid pressure.

Kinetic energy is caused by the fluids movement.

Question 33

In a venturi tube, what must a fluid do to pass through the narrow section in the middle?

Answer 33

Decrease its pressure and increases its velocity.

Question 34

What are the three types of energy involved in moving fluids?

Answer 34

1. Gravitation potential energy.
2. Pressure energy
3. Kinetic energy.

Question 35

Where might venturi tubes be used on aircraft?

Answer 35

To operate gyroscopic instruments.