Concept about Pressure – Introduction to fundamental concepts of Biological Science including the organization and common characteristics of living matters, cell structures and functions, food production by photosynthesis, harvesting energy, mechanism of cells reproduction, genetics, evolutions, and Human Biology. Introduction to general chemistry including basic concepts about matter, atomic structure, chemical bonds, gases, liquid, and solids, solutions, chemical reactions, acid, bases, and salt;
organic and biochemistry including hydrocarbons and their derivatives, carbohydrates, lipids, proteins, enzymes, vitamins, and minerals, nucleic acids; principles of physics and applications to nursing including gravity and mechanics, pressure, heat and electricity; nuclear chemistry and nuclear physics, effects of radiation on human beings, and protection and disposal. The aim of the course is to acquire knowledge and skills in general biological science, general chemistry and physics.
Concept about Pressure
Pressure is a relationship of a unit of force and a unit of area i.e., when the unit force is applied on unit area, the pressure is determined by the formula P = F/A, where P is the pressure, F is the force, and A is the area. In short, force acting per unit area is known as pressure. The unit of pressure in metric system is dynes per cm².
Basic Pressure Example
If you had 1 newton (1 N) of force distributed over 1 square meter (1 m²), then the result is 1 N/1 m² = 1 N/m² = 1 Pa. This assumes that the force is directed perpendicularly toward the surface area.
If you increased the amount of force, but applied it over the same area, then the pressure would increase proportionally. A 5 N force distributed over the same 1 square meter area would be 5 Pa. However, if you also expanded the force, then you would find that the pressure increases in an inverse proportion to the area increase. If you had 5 N of force distributed over 2 square meters, you would get 5 N/2 m² = 2.5 N/m² = 2.5 Pa.
Definition of Pressure
In science, pressure is a measurement of the force per unit area. The SI unit of pressure is the pascal (Pa), which is equivalent to N/m² (newtons per meter square).
Or
Pressure is defined as a measure of the force applied over a unit area. Pressure is often expressed in units of Pascals (Pa), newtons per square meter (N/m² or kg/m-s²), or pounds per square inch. Other units include the atmosphere (atm), torr, bar.
Pressure Units
- 1 Pa = 1 N/m²
- 1 bar = 10,000 Pa
- 1 atm≈ 1.013 × 105 Pa = 1.013 bar=1013 millibar
Types of Pressure:
The pressure is defined as the force acting per unit area. Following are the different types of pressure based on the reference pressure:
➤ Absolute pressure: Pressure which is related to reference pressure is known as absolute pressure.
➤ Differential pressure: The difference between the two pressures is equal to the differential pressure.
➤ Atmospheric pressure: Pressure related to the atmosphere that surrounds the earth is atmospheric pressure. This pressure is weather-dependent.
➤ Gauge pressure: This is the difference between absolute pressure and atmospheric pressure.
Pascal’s Law:
Neglecting gravity, the pressure at a particular depth below the surface of a fluid at rest is the same in all directions.
Applications of Pascal’s Law:
1. In B.P. instrument, the mercury manometer operates on the principle of Pascal’s law. The flow of blood in the artery is occluded by the pressure of the enclosed air in the airtight cuff. The pressure supports a column of mercury in the manometer. When the air in the cuff is released slowly and the blood just begins to flow again, the pressure is measured by the height of this mercury column.
2. The amniotic sac enclosing the fetus in the uterus is filled with amniotic fluid, which is a confined fluid and serves as a protection to the fetus. Any pressure exerted against the abdominal wall will be transmitted to the amniotic fluid to all surfaces of the fetus. To avoid unequal pressure which may cause fetal deformity, the patient is usually cautioned against wearing tight clothing during pregnancy.
3. Medicine droppers and rubber bulb syringes enclose a fluid also work on the principle of Pascal’s law. Pressure applied against the rubber bulb is transmitted to the enclosed liquid and causes it to flow from the open end of the dropper or syringe.
4. Air and water mattresses work on Pascal’s law. These mattresses are used to prevent decubitus ulcers bed sores in hospital patients.
Hydrostatic Pressure
Hydrostatic pressure is the pressure that is generated by the weight of liquid above a measurement point, when the liquid is at rest. The height of a liquid column, of uniform density, is directly proportional to the hydrostatic pressure.
Formula for calculating hydrostatic pressure
The formula for calculating the hydrostatic pressure of a column of liquid is:
- P hyd =h. rho.g
- P rel =h. rho.g
- P abs =h. rho.g+P atm
Symbols keya
- P hyd = Hydrostatic Pressure (Pa)
- P rel = Relative Pressure (Pa)
- P abs = Absolute Pressure (Pa)
- P atm = Atmospheric Pressure (Pa)
- h = Liquid Height (m)
- rho = Liquid Density (kg / m * 3)
- g = Local Gravity (m / s * 2)
Atmospheric Pressure
Atmospheric pressure, sometimes also called barometric pressure (after the sensor), is the pressure within the atmosphere of Earth(or that of another planet). The standard atmosphere (symbol: atm) is a unit of 10 pressure defined as 1013.25 mbar (101.325 kPa), equivalent to 760 mmHg (torr), 29.9212 inches Hg, or 14.696 psi. The atm unit is roughly equivalent to the mean sea-level atmospheric pressure on Earth.
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