1. Fluid Mechanics and
Thermodynamics
Day 1: Object Density and Hydrostatic Pressure
2. What is a fluid?
Fluids are anything that can flow: liquids or gases.
Fluids conform to their containers
3. What if?
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?
5. Things to know:
Density: Ratio of mass to volume of
an object
To calculate density, determine the
mass per unit volume, or:
=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
What is the specific gravity of Aluminum? What about oil?
6. Pressure
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.
7. Does AIR have pressure?
How do you know?
What about WATER?
1 atmosphere = 101.325 kPa , or about 101,300 Pa.
8. How much pressure?
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!
9. Absolute Pressure and Gauge
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
10. 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?
11. Think?
How does the pressure 6” below the surface of a
swimming pool at sea level compare to the pressure
6” below the ocean?
12. Blood Pressure?
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…
