Already in the ancient world, people suspected that such pressure air and liquids really are.Some of the ideas about the atomic structure of matter came to us in the poem Lucretius' On the Nature of Things ", and this is the period of antiquity, while the properties of the pressure effectively used in ancient Egypt.Priests with a heated and expanded gas "magic" opened the doors of temples, and the builders use hydraulic lift heavy blocks of stone.
Today, the question of what kind of pressure as the physical quantity, answer: it is the ratio of force per unit area.Therefore, air pressure, fluid pressure in the pressure vessel and the solid to support - are related phenomena.Because they involve force, pressure can be made to do the work (the enterprising and enjoyed the Ancient Egyptian priests).
With the pressure of a rigid body on a support, in principle, everything is clear.Body weight - is power, and it is divided by the area of contact with the support body.However, liquid and gas particles are not at rest.They always make a motion or chaotic Brownian or targeting due to the impact of external forces or internal conditions of the system.The pressure created by particle impact on the vessel wall.
strength, which is involved in the creation of pressure in this case - is a pulse which gives each particle per unit time.Where does the momentum and strength, we will understand if we remember the formula kinematics describing the elastic collision of bodies.A molecule or atom of liquid and gas is regarded as an elastic sphere.Inside, liquid and gaseous matter particles constantly collide with each other, exchanging energy and momentum.Therefore, the pressure also exists not only with respect to the vessel wall, but also inside any substance.Even within the vacuum
always some particles that create a slight pressure therein.It is true that such pressure exists in a vacuum, it became clear immediately.Initially it was thought that a vacuum - it is absolute emptiness, and it creates a zero pressure.Physics school course uses this assumption now.
return to the motion of particles.It will help us to understand what is the kinetic and static pressure.When the particles are in random thermal motion, which is constant, there is a static pressure.When applied to the system any external influence, and the motion of particles having prevailing direction, these same particles are beginning to have the kinetic pressure.
static pressure can be observed, for example, on the bottom of the tub filled with water.If you open the tap, shooting a jet of water will create an additional kinetic pressure.Simplistically it can be calculated based on the same considerations as described above with respect to elastic collisions of particles.The jet has a measured pulse rate and communicates with the bottom of the vessel in a collision.Full system pressure (water bath) becomes equal to the sum of the kinetic and static pressures.
