Sometimes, remembering my school years, to recall the subjects chemistry, physics.They have expanded the boundaries of my understanding of the world through the familiarity with those or other physical concepts.Some of them did not want to "take root."Probably because often voiced teacher did not have a specific definition of the physical image, and were, at first, abstract concepts.Here

meter - everything is clear.Time, too, kind of like no other questions, the clock - a favorite childhood toy, tick-tock, tirelessly.Meter, hour, second - the physical entity "grow" into consciousness.But imagine 10 km of air that "crush" on you day and night, tirelessly, and called lyrical and mysterious - atmospheric pressure.And it turns out that's not all, there is a positive pressure, and osmotic, and blood, and ... bring them numbers, all of these pressures.Later, however, everything falls into place, but judging by online forums, questions on various aspects of the concept of "pressure" was, is and will be.So what is it - the pressure?

practical meaning of the term "pressure" is that this specific power characteristic - the load per unit area.Any objects that surround us, always "supported", which puts pressure on any surface - a table, windowsill, stand, road.How to determine who is a great burden on the road - a tank or a person walking on it?Here also it helps the concept of a physical quantity "pressure", which is calculated on the basis of other physical quantities.To do this, determine the weight of the object and the area of its support.Weight divided by the square and get the pressure value - the proportion of weight per unit area of, say, a square centimeter.Now we can say for sure who is more "pressing".

And do not say now who first suggested that the "column" of air one square centimeter and a height of 100 km, this is the conventionally considered the height of the atmosphere, called atmospheric pressure.If the zero height to take sea level, then the numerical value of the atmospheric pressure Ratm, it is also called barometric amount to about 1 kg / cm sq.It so happened historically that this wonderful physical quantity - one atmosphere equal to 1 kgf / cm sq.- It has several prototypes.In particular, the widely used option measurement in millimeters of mercury - 1 atmosphere equals 760 torrAt different heights from the Earth "oppressive" air column is different, and the pressure measured by the barometer, with a change in altitude is changing.For example, at a height of 5 km barometric pressure is 405 mmHg

Other variants of the name-pressure classified according to their relation with barometric.For example, commonly used in the art gauge device measures the gauge pressure.Determination and sounds that excess pressure is considered to be in the range above the barometric and Rati represent him.In technical applications, it is often measured by the excess pressure.

Maybe less than the atmospheric pressure?Of course, in this case, under vacuum or is called.The absolute vacuum - this pressure of absolute zero - less does not happen.Therefore, if you take it as a starting point, any pressure greater than zero is called an absolute varies from zero to any value, and represent his Manpower.

How to calculate the excess pressure?The formula for calculating the absolute pressure is of the form:

Manpower = Ratm + Rati

It is not difficult to calculate the excess pressure, the difference:

Rati = Manpower - Ratm

pressure having a simple analytical expression, unfortunately, has such a hugethe number of units that they understand only experts.The most useful of these is a bar, Pascal, kg / sq cm.and their derivatives with prefixes mega, hecto, gig.

The SI unit of pressure - Pascal - is a force of one newton in on an area of one square meter.By itself, the n / m sq.such a small quantity that it is used in practice, the derivative of a bar that is approximately 100 kPa or 750 mm Hg, i.e.almost 1 kg / cm sq.Here it is, the circle closed up - again we come to the beautiful and poetic unit of pressure - the atmosphere.However, in this case, it is called "technical atmosphere" and that this unit often, by force of habit, the excess pressure is measured.A complete list of conformity applied in different areas of pressure takes pages of fine print.

So, simple and clear pressure has grown into a tangled maze of their own units.But there is no reason to worry - there is always a handy reference book or online ....