What do we know about vacuum?

2024 Author: Seth Attwood | [email protected]. Last modified: 2023-12-16 15:55

In the strictest sense, a vacuum is a region of space in which matter is completely absent. This term represents absolute emptiness, and its main problem is that it describes an ideal state that cannot exist in the real world.

No one has yet found a way to create an ideal vacuum of this type in terrestrial conditions, and for this reason the term is also used to describe empty regions of space. But there is still a vacuum in areas that are a little closer to our daily life. We will tell you what it is in simple words.

In most cases, a vacuum is a container from which all gases, including air, are removed as much as possible. Outer space is indeed closest to an ideal vacuum: astronomers believe that the space between stars in some cases consists of no more than one atom or molecule per cubic kilometer.

No vacuum produced on Earth even comes close to this condition.

To talk about the "earth vacuum", you need to remember about pressure. Pressure arises from the effect of molecules in a gas or liquid on their environment, usually on the walls of the containing vessel, be it a soda bottle or your skull. The magnitude of the pressure depends on the strength of the blows that the molecules "inflict" on a certain territory, and is measured in "newtons per square meter" - this unit of measurement has a special name "pascal".

The relationship between pressure (p), force (F) and area (A) is determined by the following equation: p = F / A - it applies regardless of whether the pressure is low, as, for example, in space, or very high, as in hydraulic systems.

In general, although the definition of vacuum is inaccurate, it usually refers to pressure below, and often well below atmospheric pressure. A vacuum is created when air is removed from an enclosed space, resulting in a pressure drop between that space and the surrounding atmosphere.

If the space is limited by a moving surface, atmospheric pressure will compress its walls together - the amount of holding force depends on the surface area and the vacuum level. As more air is removed, the pressure drop increases and the potential force of the vacuum also increases.

Since it is almost impossible to remove all air molecules from the container, it is impossible to achieve a perfect vacuum.

On an industrial and home scale (for example, if you decide to put a winter down jacket in vacuum bags), the effect is achieved by using vacuum pumps or generators of different sizes, which remove air. A piston-in-cylinder pump is attached to a closed container, and with each pump stroke, a portion of the gas is removed from the cylinder. The longer the pump runs, the better the vacuum is created in the tank.

Anyone who has ever evacuated air from a bag for storing clothes, squeezed the lid of a plastic container to release air from a container, or put cans (and also went for a vacuum massage), has encountered a vacuum in his life. But, of course, the most common example of its use is a regular household vacuum cleaner. The fan of the vacuum cleaner constantly removes air from the canister, creating a partial vacuum, and the atmospheric pressure outside the vacuum cleaner pushes air into the canister, taking with it dust and dirt that is agitated by the brush at the front of the vacuum cleaner.

Another example is a thermos. A thermos consists of two bottles nested inside each other, and the space between them is a vacuum. In the absence of air, heat does not pass between the two bottles as easily as it normally would. As a result, hot liquids inside the container retain heat, while cold liquids remain cold because heat cannot penetrate into them.

So, the vacuum level is determined by the pressure difference between the interior and the surrounding atmosphere. The two main landmarks in all of these measurements are standard atmospheric pressure and ideal vacuum. Several units can be used to measure vacuum, but the common metric unit is millibar, or mbar. In turn, atmospheric pressure is measured by a barometer, which in its simplest form consists of an evacuated vertical tube with a closed upper end and a lower end, located in a container with mercury open to the atmosphere.

Atmospheric pressure acts on the exposed surface of the liquid, causing the mercury to rise into the tube. "Normal" atmospheric pressure is the pressure equal to the weight of a 760 mm high mercury column at a temperature of 0.0 ° C, latitude 45 ° and sea level.

The vacuum level can be measured with several types of pressure gauges:

• Bourdon tube pressure gaugeis the most compact and most widely used device - the measurement is based on the deformation of a bent elastic tube when a vacuum is applied to the pressure gauge port.

• The electronic analogue is vacuum gauge … Vacuum or pressure deflects an elastic metal diaphragm in the sensor, and this deflection changes the electrical characteristics of the interconnected circuit - the result is an electronic signal that represents the vacuum level.

• U-tube pressure gauge shows the difference between two pressures. In its simplest form, this gauge is a transparent U-tube half filled with mercury. When both ends of the tube are at atmospheric pressure, the level of mercury in each elbow is the same. Applying a vacuum to one side causes the mercury to rise and fall on the other side - the difference in height between the two levels indicates the vacuum level.

On the scales of most pressure gauges, atmospheric pressure is assigned a value of zero, therefore, vacuum measurements should always be less than zero.