# Dynamics - Fluid Mechanics Flashcards

Fluid

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

Examples of fluids

Gases or liquids

Liquid differ from gas…

Intermolecualr forces keeping them together.

Densit

Mass divided by volume occupues, or mass per unit volume

How density differs with material?

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

Force in a fluid..

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

Example of a surface and a fluid presse.

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

Equation for pressure?

p = F/A

How is pressure measured?

In pascals.

Describing pressure in a fluid…

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.

What is dp/dy equal to?

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

Hydrostatic Equilibrium

The balance between the pressure gradient force and gravitational pull.

What is the pressure difference between two points equal to?

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

Pascals Law

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

Absolute Pressure

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