Fluid Mechanics and Thermodynamics

Day 1: Object Density and Hydrostatic Pressure

Fluids are anything that can flow: liquids or gases.

Fluids conform to their containers

What is a fluid?

What if I had a piece of material like the cylinder shown, and I wanted to know what material it was?

Brainstorm… What methods could you use to determine if they were the same?

What if?

What am I?

Density: Ratio of mass to volume of an object

To calculate density, determine the mass per unit volume, or:

r =m/v

Density (kg/m3) is an intrinsic property of matter.

Specific gravity: The ratio of an objects density to that of water at 4°C

Things to know:

What is the specific gravity of Aluminum? What about oil?

Pressure is force/area

In pascals (Pa) = N/m2

Example: A cat with mass 20 kg walks across the snow. If snow collapses under a pressure of 0.5 psi (2500 Pa), determine the minimum size of the cat’s paws.

Pressure

Does AIR have pressure?

How do you know?

What about WATER?

1 atmosphere = 101.325 kPa , or about 101,300 Pa.

My fish tank is 10 gallons. (I googled: 10 gallons = 0.0379 m3)

How much pressure does the top (open) surface of my tank experience?

How about the bottom?

*Note that we’re only interested in the pressure downwards on the floor of the tank. The sides cancel out!

How much pressure?

The pressure at any depth is the sum of the weight of the fluid and

the atmosphere:

P = P0+ρgh

ρ = fluid’s density, g = 9.8 m/s2, and h = height of water column/ depth

Absolute Pressure and Gauge Pressure

A foolish boy tries to use a garden hose for air as he swims at the bottom of a 5.00 m deep pool. What goes wrong?

Absolute Pressure and Gauge Pressure

Think?

How does the pressure 6” below the surface of a swimming pool at sea level compare to the pressure 6” below the ocean?

Use a blood pressure cuff (sphygmomanometer) to measure the maximum and minimum pressure exerted by your heart.

Restrict blood, then release until the very first push: systolic: heart generates its maximum pressure.

Keep relieving pressure (letting out air) until blood flows continuously: part of hearbeat cycle when pressure is lowest: Diastolic.

120/80 is typical…

Blood Pressure?

Chapter 14: Read 14.1-14.7 Do #3.1, 4.1, and 6.2

HW: Due Friday