Hydromechanics
Hydromechanics, the branch of physics that deals with forces acting upon and within fluids (liquids and gases). Hydromechanics is divided into hydrodynamics, the study of fluids in motion; and hydrostatics, the study of fluids at rest.
Principles of the hydromechanics of fluids are applied in hydraulics, which deals with water and other liquids at rest or in motion; in aerodynamics, which deals with the motion of air and with the relative motion between air and objects in the air; in fluidics, which deals with automated sensing and controlling devices that use the movements of fluids to operate ; and in pneumatics, which deals with the mechanical properties of gases .
HydrodynamicsA liquid or gas flows from regions of high pressure to regions of low pressure. This happens, for example, when water is squeezed from a sponge or squirted from a hose.
The flow of a fluid is influenced by viscosity, the resistance that opposes the motion of a fluid. Some liquids flow by capillary action, which depends largely on adhesion and surface tension.
The flow of a liquid or gas can be laminar (smooth) or turbulent (rough and eddying). The nature of the flow depends on the viscosity and density of the fluid, on the speed at which the fluid is moving, and on the surface and shape of objects in contact with the fluid. For example, water flows turbulently along the rough banks of a river but flows laminarly around the smooth, curved sides of a boat floating in the river. An object whose shape offers little resistance to the smooth flow of a fluid is said to be streamlined.
Bernoulli's Principle,discovered by the Swiss physicist Daniel Bernoulli (1700-1782), states that the pressure exerted by a flowing fluid on the walls of a tube (for example, a hose or pipe) decreases where the speed of the fluid increases (as at the exit from a nozzle). Bernoulli's Principle explains the “lift” obtained by hydrofoil boats and by aircraft with wings or rotors.
The effects explained by Bernoulli's Principle can be produced by sending a fluid through a venturi tube, or venturi, a short tube whose diameter tapers to a relatively narrow section at its middle. The speed of the fluid in this narrow section is greaterand its pressure lessthan in the rest of the tube. The venturi tube is used in several kinds of devices, including instruments that measure flow of fluids.
Torricelli's Theoremis an application of the Law of Falling Bodies to liquids. This theorem was derived by the Italian physicist Evangelista Torricelli (1608-1647). It states that a liquid flowing from an outlet in a tank has the same speed as an object falling freely from the level of the liquid's surface to the level of the outlet. The theorem also states that a jet of water rises to the level of its source, unless opposed by friction. Torricelli's Theorem explains the action of an artesian well.
HydrostaticsArchimedes' Principlestates that a fluid exerts a buoyant (lifting) force on an object placed in the fluid. The force is equal to the weight of the fluid displaced by the object. The principle, discovered by the Greek mathematician Archimedes, explains why ships float in water and balloons in air.
Pascal's Law,formulated by the French philosopher Blaise Pascal (1623-1662), applies to any fluid at rest in a container. The law states that pressure upon the fluid at any point will be transmitted uniformly throughout the fluid. In the case of a gas, a pressure increase causes compression (uniform lessening of volume). Liquids, however, are not compressible. An increase of pressure at any piont upon a contained liquid will result in an increase of pressure at every point upon the walls of the container; the volume of the liquid remains the same. Pascal's Law explains the action of a hydraulic press and similar devices.