Lecture 27 - Recorded on November 15, 1999
Pressure in a Static Fluid
Video Lectures: (RM-80K) (RM-300K)
Concepts covered in this lecture include gases and incompressible liquids, Pascal's Principle, hydrostatic and barometric pressure.
Lectures.
| SEG # |
SEGMENT TITLES |
SEGMENT TOPICS |
STARTS AT (MIN:SEC) |
| 1 |
Pressure and Pascal's Principle |
Pressure is a scalar. Pascal's Principle is explained. In hydraulic jacks, a small force is applied to move a large mass a small distance. |
00:00 |
| 2 |
Gravity and Hydrostatic Pressure |
Because of gravity, pressure increases with depth in a fluid. This is called hydrostatic pressure. |
07:31 |
| 3 |
Compressibility of Gases vs. Liquids |
Unlike liquids, gases are compressible, so they cushion impacts. Liquids do not act like cushions. This is demonstrated in a very dramatic way by firing a bullet in a sealed can filled with air and one filled to the brim with liquid. |
12:37 |
| 4 |
Pressure Difference and a Column of Liquid |
The pressure difference between the bottom and top of a vessel of liquid depends only on the height and density of the liquid, not on the area or weight of the column. This is rather non-intuitive. |
16:16 |
| 5 |
Atmospheric or Barometric Pressure |
The pressure at sea level due to the air above determines the atmospheric or barometric pressure. It can be measured by raising (sucking up) a column of liquid from an open reservoir with a tube sealed at the end where we pump the air out. For every 10 meters depth in water, the hydrostatic pressure increases by about one atmosphere. |
20:49 |
| 6 |
Submarines and Overpressure |
Cornelis Drebbel is credited with inventing the first submarine operating at a depth up to 5 meters. At this depth, the hydrostatic pressure is about half an atmosphere. A sealed paint can was evacuated to demonstrate the enormous forces acting upon it with an over pressure of about one atmosphere. The can imploded. |
30:34 |
| 7 |
Overpressure in our Lungs |
The lung capacity, our ability to overcome hydrostatic pressure, is measured with a manometer. This is related to how deep snorkeling works, and why scuba-divers use pressurized air tanks. Professor Lewin demonstrates that by blowing on a manometer, or by sucking on it, we can raise or lower a column of water by about 1 meter (0.1 atmosphere). So why then was he able to suck fluid up a straw of several meters long? |
35:44 |