What is Simple define of pressure and units of pressure

 Pressure:. Imagine that you are standing on the surface of road ,your feet exerts force on the earth. The area under your shoe bears the force of your body. The ratio of the applied force to the area is called pressure. When you talk about a high heel, the high hell exerts more pressure on earth than the shoe, because the area is small but the force is same. For example a man is Sitting on a ground; the weight is the force which is acting on the surface of earth. The force ( weight of man) acted upon the area he covers while sitting cause the pressure of the man on the earth.But a man is standing applies the same force ( weight) with different area in contact with the surface and therefore exert a different pressure.         

Different Area in contact will give different value of the pressure .                                           Perssure is defined as force per unit area.      It is usually more suitable to use pressure rather than force to describe the fluid behavior the standard unit for pressure is the pascal, which is a Newton per square meter.      Where:.     P= F/A p is the pressure,.           F is the normal force,  A is the area of the surface area on contact             There are many common physical examples where pressure is the most important variable . If you peel some apple you actually apple pressure on the apple with the help of a knife. As the knife edge is sharp you have to apply less force ,because the area of contact of the apple and the knife is small. If you visit a doctor and he advises you to get an injection. The sharp needle can pass the right pressure as compare to a dull one . The smaller area of contact involves less force for the needle to push through the skin . As we all know that the fluids exert pressure . The individual molecules of the fluid, however ,are in constant random motion .In the fluids ,there are extremely huge amount of molecules and because the movement of the particular molecules is random in every direction so we do not specify the motion . If we fill a container with some fluid ( either gas or liquid) ,we can detect a pressure in the fluid from the molecules ,which have a collision with the walls of container .we can put the gas in the container ,and the force per unit area ( the pressure) is the same. Similarly pressure acts in all directions at a point inside a fluid. At the surface of a fluid , direction of the pressure acts at right angle to the surface. Pressure is the effect of a force applied to a surface. Pressure is a scalar quantity. The transmission of pressure from the fluid to the solid boundaries is always perpendicular to that surface at every point.                             

Pressure as exerted by particle collisions inside a closed container.                                     Absolute pressure:. The absolute pressure is measured relative to the absolute zero pressure. Absolute pressure is pressure that would occur at absolute vacuum, or zero pounds per square inch ( PSI) .All calculations concerning the gas laws have need of pressure ,and temperature in absolute units. Absolute pressure is actually referred as total system pressure ,. To differentiate it from gauge pressure ,the term abs is usually placed after the unit. The absolute pressure ,pabs is measured relative to the absolute zero pressure . It is the pressure that would occur at absolute vacuum. All calculation involving the gas laws requires pressure ( and temperature ) to be in absolute units.                                           pbs= pg + patm.                                                      Gauge pressure:.   A gauge pressure is often in use to measure the difference between a system pressure and it's environment ( surrounding) pressure . The gauge pressure actually has shown on the dial of a gauge gives record of the pressure relatives to atmospheric pressure. For example if a pressure gauge gives the reading of zero value ,it does not mean that there is no pressure acted upon the fluid ,actually it means that there is no pressure in addition of to the atmospheric pressure .this pressure is often called the gauge pressure and can be expressed a                                                               where.        Pg = pabs - patm.                                                   Pg = gauge pressure                                               ps = Absolute pressure.                                         Patm= atmospheric pressure.            Atmospheric pressure:.  Atmospheric pressure can be defined as the force exerted by the weight of air just above that surface per unit area applied against that surface .think in terms of air molecules, if the quantity of the air molecules above a surface increase quantity of air molecules above that surface will give Low pressure in result.          

The relationship among the absolute ,atmospheric and gauge pressure .                         Atmospheric pressure is measured with an instrument called a barometer ,that is why atmospheric pressure is also called as barometric pressure.                                             units for pressure:.   *The SI unit for pressure is pascal (pa) ,equal to one Newton per square meter ( N/m2.  Or kg m-1 .s-2).         *The British system measures in pounds per square inch.  *The CGS unit of pressure is the barye (ba) ,equal to 1 Dyn cm2 or 0.1 pa. Pressure is sometimes expressed in grams force /cm2 ,or as kg/ cm2 .      Standard atmosphere= 101,325pa=101.325 kpa.                 Example problem 01: A women has 550 N weight and she wears the high heel shoes that come into contact with the ground over an area of 425 cm2.