Fourth year of secondary education
Pressure (I)
E. Vallo - J.Villasuso
 Pressure
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Manometers 2 / 3

This manometer contains mercury and measures the pressure of the gas in the receptacle on the right.

Observe the manometer when you vary the temperature of the gas.
Remember that the pressure at two points  in the tube situated at the same height is the same: pA = pB
Pressure at point A is that due to the atmosphere and to the column of liquid above A, of a height h.
The pressure at point B is due to the gas.
Ppressure of the gas = P atm. + dliquid ·g · h

To calculate the manometric pressure
p = dliquid ·g · h, you only need to measure h, as the density of the liquid in the manometer is known.

In manometers you don't have to calculate this as there is a calibrated scale in pressure units on branch A.
It should be remembered that what the manometer measures is the so-called manometric pressure, which is the value of the pressure of the gas once atmospheric pressure has been deducted.

 

What is pressure? How does it work?
Units
Hydrostatic pressure
Mathematical expression
The pressure increases the deeper you go in liquids
Which goes the furthest?
A little goes a long way!
Communicating vessels
Syphons
Pascal's Law
The Law
The hydraulic press
Hydraulic brakes: drum brakes
Manometers
Problems
Evaluation