This SIR illustrates the operation of a mercury barometer and closed-tube and open-tube manometers. It allows the instructor to show how a Torricelli vacuum is formed, and explore how pressure does not change perceptibly with elevation in a meter or two of air (density about one gram per litre), while it increases dramatically as one moves down into dense mercury (density 13.6 kilogram per litre).
The main menu gives you the choice of four animations, and also allows you to reset the value of the atmospheric pressure to any value between 650 and 800 torr. On every animation, you may click to mark any spot in gas, air, mercury or vacuum. A second click there reveals the pressure at that point.
Torricelli Vacuum
This starts with an inverted tube full of mercury immersed in mercury. You may cause the tube to slowly rise out of the mercury; at a certain point the mercury in the tube breaks away from the top, leaving a vacuum.
Barometer is essentially the final state of the Torricelli animation. You may explore how pressure falls as you go up the mercury column, from atmospheric at the bottom to zero at the top.
Closed and Open Tube Manometers
These manometers differ only in that the first has the mercury exposed togas and to vacuum. The second has it exposed gas and to 760 torr (or whatever atmospheric pressure you have set).
There is a facility to raise or lower the gas pressure.
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Updated July 25, 2000