Suction

Maelstrom is the everyday term for a suction that objects in the vicinity of moving gases and liquids ( fluids ) experience.

The term " sucking " is misleading and requires the existing on earth air pressure, because more of the pressure difference over another volume shall prevail.

Operation

The following thought experiment will show that " sucking " is a very superficial description to generate a negative pressure in a room, so that a gas or a liquid is driven into by the excess pressure of an adjacent space:

• A jet pump would operate on the moon (where there is a vacuum ) would remain in the container, the suction medium, because there is no pressure pushing the molecules from the reservoir into the ejector pump. As you get used to the earth at the effect of the air pressure, the effect of being able to press a liquid from a container against the effects of gravity upward into a space of lower pressure, often criticized as being "normal " is assumed.
• A gas or liquid can in principle neither suck nor pull, because the cohesive forces (van der Waals forces ) are much too low to accelerate other molecules appreciably.
• The necessity of having to actually press the suction medium in the pump, it immediately becomes clear if one imagines a second thought experiment, the suction medium is water, which is located in more than 10 m depth in a well. In this case, you can with no suction pump water (see # air pressure experiments and measurement).

By locally varying flow velocities occur in accordance with the law of Bernoulli different static and dynamic pressures. These pressure differences disturb the balance of a body in flow. The result is a force tending to move it. The body is pressed by the higher pressure in the lower pressure, hence the term suction is actually wrong.

Such suction effects is used, for example, in the water-jet pump, in which by means of a venturi tube a negative pressure can be generated.

When boats are called analogous to the process Lenzen. The flowing water to the boat to generate the hull around vacuum the higher air pressure in the hull presses water or air through the drainage valve to the outside. When driving slowly to the external negative pressure is not sufficient, then the reversal of flows must be prevented in the boat. In ships with a lot of depth, the speed is not enough to achieve the necessary vacuum in several meters of water depth at Kiel.

Ships be vented without a fan, when the wind generates around a Dorade fan vacuum. A comparable effect is observed when you look with open mouth 'in the Wind " turns in a storm.

The term pull back a strong flowing beneath the surface in the direction of flow of the ocean surf is also referred.

• Fluid Mechanics