Dynamics - Fluid Mechanics

Question 1

Fluid

Answer 1

A substance that flows/changes shape of the volume it occupies.

Question 2

Examples of fluids

Answer 2

Gases or liquids

Question 3

Liquid differ from gas…

Answer 3

Intermolecualr forces keeping them together.

Question 4

Densit

Answer 4

Mass divided by volume occupues, or mass per unit volume

Question 5

How density differs with material?

Answer 5

Air is 1.20kg/m3 whilst ice 0.92x10^3 kg/m3

Question 6

Force in a fluid..

Answer 6

Any surface in contact with the fluid due to collisions by the molecules

Question 7

Example of a surface and a fluid presse.

Answer 7

A surface in a fluid to remain at rest must experience equal magnitude of force on both sides.

Question 8

Equation for pressure?

Answer 8

p = F/A

Question 9

How is pressure measured?

Answer 9

In pascals.

Question 10

Describing pressure in a fluid…

Answer 10

Bottom and top have area A with elevations y and y+ dy respectively, with volume dV = A dy, mass is dm = p dV = pA dy and weight is dw = dm g = pgA dy.

Question 11

What is dp/dy equal to?

Answer 11

Negative density x gravity, so as y increases, pressure decrease, pressure decreasing as move up in the fluid

Question 12

Hydrostatic Equilibrium

Answer 12

The balance between the pressure gradient force and gravitational pull.

Question 13

What is the pressure difference between two points equal to?

Answer 13

The negative density x gravity x by change in heights of the two points.

Question 14

Pascals Law

Answer 14

Pressure applied to an enclosed fluid is transmitted undiminished to every portion of the fluid and the walls of the containing vessel.

Question 15

Absolute Pressure

Answer 15

This is the pressure of having no matter inside a space, or a perfect vaccum

Question 16

Gauge Pressure

Answer 16

The excess pressure above atmospheric pressure

Question 17

What does P0 - p = -pg(y2-y1) -pgh tell you?

Answer 17

That pressure p at depth h is greater than pressure p0 at surface by an ammount of pgh

Question 18

When is gauge pressure negative?

Answer 18

If pressure is less than the atmosphere

Question 19

Archimedes Principle

Answer 19

This says that when an object is completelty or partially immersed in a fluid, the fluid exerts an upward force on the object equal to the weight of the fluid displaced by the object.

Question 20

Description of archimedes principle..

Answer 20

Object buoyancy, each point of an object is acted on by dF, sum of the surface forces equal in magnitude to the weight of fluid inside the sruface

Question 21

For a body to float in air…

Answer 21

Its total weight must equal the weight of air displaced by the body…

Question 22

Why does buoynacy occur…

Answer 22

The fluid below an object exerts greater pressureo n the object than the fluid above it due to difference in pressure between top and bottom of the submerged object.

Question 23

Ideal Fluid

Answer 23

Describes an incompressible fluid meaning density cannot change.

Question 24

Flow Line

Answer 24

Measures path of a particle

Question 25

Streamline

Answer 25

A line that is tangenital to the instantaneous velocity direction.

Question 26

Laminar Flow

Answer 26

This is where two or more streams of fluid flow adjacenet without mixing other than by diffusion across their boundary

Question 27

Turbulent Flow

Answer 27

These are irregulary motions of the fluid elements from high flow rates of abrupt velocity changes

Question 28

Continuity Equation

Answer 28

This is that mass input minus the mass outpue equals the change of mass

Question 29

Description of con equation…

Answer 29

A1 and A2 with velocities V1 and V2 during dt move a distance where volume at A1 is the same at A2

Question 30

Bernoullis Principle

Answer 30

Says that an increase in speed of fluid occurs simultaneously with decrease in static pressure

Question 31

Mass Flow Rate

Answer 31

The mass of a substance of which pressure passes per unit time.