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# Video Index for Lecture 27

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