We explain what pressure is and the types that exist. Also, examples of this physical magnitude and its relationship with temperature.
What is pressure?
The pressure is a scalar physical quantity represented by the symbol p which designates a projection of force exerted perpendicularly on a surface, per unit area.
Pressure relates a force of continuous action and a surface on which it acts, which is why it is measured in the International System (SI) in pascals (Da), each equivalent to one newton (N) of force acting on one square meter (m2) surface. In the English system, however, the measurement of pounds is preferred (pounds) per inch (inches).
Matter is commonly subjected to different pressures. For example, a gas within a certain volume will exert greater pressure if its temperature is increased. In general, the pressure changes to which the matter is subjected can force it to change its state of aggregation, that is, go from gas to liquid, for example, as is usually done with hydrocarbon gases.
Other units of pressure measurement include the bar (10N/cm3), the atm or atmosphere (equivalent to about 101325 pa), he Torr (equivalent to 133.32 pa), and millimeters of mercury (mmHg). The device designed to measure pressure is known as blood pressure monitor.
See also: Boiling point
Types of pressure
Pressure can be classified according to the following types:
- Absolute It is the pressure exerted on a body by the action of some element, plus the atmospheric pressure it suffers (all bodies on the planet are subject to atmospheric pressure).
- Atmospheric It is the pressure exerted by the entire mass of gases in the atmosphere on the Earth's surface and on everything that rests on it. As one rises above sea level (in an airplane, or climbing a mountain), atmospheric pressure decreases since there is less air mass above us.
- Manometric It is the pressure that exists above the atmospheric pressure value. Also called relative pressure, its value corresponds to the difference between absolute pressure and atmospheric pressure. Relative pressure is measured using a manometer (hence its name) and is the one most used in everyday life.
- Hydrostatic or hydrodynamic It is the pressure experienced by fluids, both due to the weight of the fluid itself at rest (hydrostatic), and in constant motion (hydrodynamics). Usually an average pressure between the two is calculated.
Examples of pressure
Some everyday examples of the action of pressure can be:
- Pressure cookers These pots specially designed to quickly soften food operate based on a strong grip between lid and pot which, by increasing the temperature and, therefore, the pressure of the content, makes the food soften faster.
- Refrigeration Freezers and other refrigeration appliances operate by circulating a pressurized liquid or gas through a pipe. Through a circuit in which pressures increase and decrease (also increasing and decreasing the temperature of the surrounding liquid or gas), the refrigeration device removes heat by contact.
- Hydraulic brakes Designed to prevent cars and other vehicles from overturning, they work by keeping brake fluid pressure high or low as required at the time, to soften the braking action and minimize the risk of skidding and overturning.
- The immersion When being underwater, for example, diving, the action of the mass of water on the body is perceived as a more intense form of pressure. This can cause physical damage when you are miles below the surface.
Pressure and temperature
Pressure and temperature are closely connected. When a compressible substance (such as a liquid or, better yet, a gas) is subjected to high pressures that force its particles (ordinarily dispersed) to approach each other and vibrate with greater speed, an accumulation of energy occurs that It is usually released as heat. Indeed, the higher the speed of the particles, the higher the temperature.
This relationship is described by Gay-Lussac's Law, which establishes a direct proportion between the pressure of a fixed volume of an ideal gas and its temperature, according to the formula:
P/T = k
Where P is pressure, T is temperature and k is a constant.
