For the owners of cat :

Here how to make. Reverse a glass on the neck of the bottle. Now, shift the whole, while maintaining glass on the neck. Surprised ! Only little water runs out of the bottle. And here it is, the bottle is reversed in the glass, and not only one water drop of lost !

Do you want to know a little bit more ? Raise the bottle so that the neck is to approximately 2 cm above the surface of water. Water runs out of the bottle and stops as soon as the level of the liquid reaches the neck. The same phenomenon is repeated each time that the bottle is slightly raised.

How that is it explained? When you shifts the bottle in the glass, a little water escapes. As the air cannot penetrate in the bottle, because of the water film, a vacuum is formed inside the bottle. At this time, the atmospheric pressure prevents water from running out more

By raising the bottle with the top of the water in the glass, the air penetrates by the neck, taking the place of the water which can again enter in the glass. When it reaches the neck, the water in the glass prevents the air from penetrating in the bottle, the vacuum is created again and water ceases running out.

For the historians :

Evangelista Torricelli (1608 - 1648) was a mathematician and an Italian physicist.

The fountain-makers of Florence had noticed that the suction pumps did not make it possible to raise the water of more than one ten meters. Galileo, questioned on the cause of this limitation, decided of the existence of a "force of the vacuum", explanation which appeared unsatisfactory for other situations.

Torricelli made experiments with various liquids, of which mercury, consisting in leaving partially of a container a tube filled and reversed, to note that the liquid goes down in the tube only from one certain height. He supported the explanation of the phenomenon by the existence of the atmospheric pressure: the air weighs on the surface of the liquid in the container, pushing the liquid in the tube, this push being seen balanced by the weight of the liquid contained in the tube. Torricelli noted that mercury went up 76 cm in the tube and he predicts that water would go up 10 m, on the basis of report/ratio of the unit weights of these two liquids.

Mersenne, of passage to Florence, brought back this work to his Parisian entourage, arousing a keen interest. Pascal was to check, in 1648, the announced result.

Torricelli also observed that the height of mercury could vary simultaneously according to the weather situation.

For the scientists :

Key concepts

The pressure (P) is the force acting perpendicularly with a given surface.

P =

F A

The pressure is a scalar size which appears in all the directions.

The fundamental unit of the pressure is N/m2. The derived unit is Pascal (Pa).

Meteorologists express the pressure in millibars.

1 mb = 0,10 kPa

1 Pa = 1 N/m², 1 kPa = 1 x 10³ Pa

A Pascal is a value of relatively small pressure, about equivalent to the pressure exerted by a  five dollars note on a plane surface.

The normal atmospheric pressure is worth 1,013 X 105 Pa or 101,3 kPa.

The atmospheric pressure decreases when one rises in altitude.

The normal atmospheric pressure supports a mercury column 760 mm height, which one expresses by 760 mm of Hg or 760 torr. A barometer is used to measure the atmospheric pressure.

The pressure (P) exerted by an incompressible fluid is directly proportional to the depth of the fluid (h), its density (r) and the intensity of the gravitational field (r). The pressure is independent of total volume or the shape of the container.

P = rgh

The absolute pressure (P_abs) is the pressure measured in reference to a null pressure. The manometric pressure (P_G) is a measurement of the difference between the absolute pressure and the atmospheric pressure atmosphérique (P_atm).

P_abs = P_G + P_atm

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