What is the pressure?

We explain what the pressure is and the types that exist. In addition, examples of this physical magnitude and its relation to temperature.

1. What is the pressure?

It is known as pressure  to  physical scalar represented by the symbol  p , designating a projection force exerted perpendicularly on a unit area; In other words, it represents how to apply a resulting force on a line.

It relates a continuous force of action and a surface on which it acts, so it is measured in the International System (SI) in pascals (Pa), each equivalent to a newton (N) of force acting on a cubic meter (m3) of surface. In the English system, on the other hand, the measure of pounds ( pounds ) per inches ( inches ) is preferred .

It is also one of the forces which are commonly subjected matter (such as temperature), and whose handling has numerous practical applications. One of them is that the increase in pressure at which matter is found can force it to change from aggregation state , that is, to pass from gas to liquid, for example, as is usually done with hydrocarbon gases.

Other units of it, measurement include bar (10N / cm3), atm or atmosphere (equivalent to about 101325 pa), or Torr (equivalent to 133.32 pascals) and measurable in millimeters of mercury (mmHg). The device designed to measure it, is known as a  tensiometer .

2. Types of pressure

Depending on the conditions in which it occurs, it can be classified according to the following types:

• Absolute . Designed as a measure to standardize the pressure, it load that a fluid experiences when in perfect vacuum or absolute zero (-273.15 ° C) is considered.
• Atmospheric . It is the one that exerts the whole mass of gases of the atmosphere on the earth’s surface and on everything that rests on it. As it rises (on a balloon or an airplane, or on a mountain) the pressure exerted will be less as there is less air mass on us.
• Manometric . When it is measured with absolute vacuum (negative pressure), absolute pressure is referred to; while comparing it against atmospheric pressure, we will talk about the gauge, and it is calculated by subtracting the first from the second.
• Hydrostatic or hydrodynamic . That experienced by fluids, both due to the weight of the fluid itself at rest (hydrostatic), and in constant motion (hydrodynamic). Usually an average pressure is calculated between the two.

3. Examples of pressure

Some everyday examples of the action of it can be:

• The cookers . These pots specially designed to quickly soften the food, operate based on a strong grip between the lid and the pot, so that by increasing the pressure of the content, the action of heat is multiplied and the food softens faster.
• Cooling . Freezers and other refrigeration devices operate by circulating a pressurized liquid or gas through a pipe, causing it to pass from a very high pressure to a very low pressure, cooling and removing heat by contact within the appliance.
• Hydraulic brakes . Designed to prevent overturns of cars and other vehicles, they work by keeping the brake fluid pressure high or low as required at the time, to soften the braking action and minimize the risk of skidding.
• Immersion . Being underwater , for example, while diving, the action of the body of water on the body is perceived as a more intense form of pressure. This can even lead to physical damage when it is miles below the surface.

4. Pressure and temperature

Both are intimately connected . When a compressible substance (such as a liquid, or better still, a gas) is subjected to high pressures that force its ordinarily dispersed particles to approach each other and vibrate faster, an accumulation of energy occurs that It is usually released as heat.

This relationship is described by the Gay-Lussac Law, which establishes a direct ratio between the pressure of a fixed volume of a gas and its temperature, according to the formula:

P / T = k

Where P is pressure, T is temperature and k is a constant.

Other evidence of this occurs when ascending in the atmosphere , where a loss of pressure is experienced, not having so much air on top of it, and at the same time a loss of heat is experienced.