What is fluid mechanics?

Fluid mechanics is a branch of physics that studies how fluids respond to forces. It's a part of classical physics with important uses in hydraulic and aeronautical engineering, chemical engineering, meteorology, and zoology. Hydraulics is a branch of science that deals with practical uses of fluids, mostly liquids, in motion and is related to fluid mechanics, which gives it its theoretical basis.

What does the term 'hydraulics' mean?

Hydraulics is a science focused on the practical uses of fluids, mostly liquids, in motion. It's linked to fluid mechanics, which gives it a theoretical base. Hydraulics looks at how liquids flow in pipes, rivers, and channels, and how they're held in place by dams and tanks. Its rules can also apply to gases, especially when density changes are small. So, hydraulics covers things like fans, gas turbines, and pneumatic control systems. Hydraulic power systems are used in many industries, agriculture, and defense. Modern aircraft, cars, industrial machines, and machine tools use hydraulic power a lot.

How do liquids and gases behave differently in hydraulics?

In hydraulics, both liquids and gases adhere to Pascal's principle , which states that pressure changes in a closed container are transmitted equally throughout the fluid. However, they differ significantly due to their distinct properties. Liquids, the primary fluids in hydraulics, are nearly incompressible, providing efficient power transmission. Hydraulic fluids, such as oil or glycerol, have low viscosity and are used in hydraulically operated mechanisms like brake cylinders. Gases, on the other hand, are highly compressible. While they can be used in pneumatic systems, which often employ compressed air to power tools and devices, their compressibility makes them less suitable for hydraulic applications requiring precise and immediate force transmission. Gases have lower viscosity and greater compressibility than liquids, resulting in lower film thicknesses and load capacities.

What is pressure in a fluid, and how is it measured?

In fluid mechanics, pressure in a fluid is the perpendicular force exerted per unit area within the fluid. In a fluid at rest, this pressure acts equally in all directions, a principle known as Pascal's law . Pressure is measured using instruments like pressure gauges . Common types include U-tube manometers for static pressures and Bourdon-tube gauges for higher pressures in liquids and gases. These gauges measure the difference between two pressures, known as the gauge pressure.

How does hydraulics make it possible to lift heavy objects with little force?

Hydraulics makes lifting heavy objects with little force possible through Pascal's principle . This principle states that pressure changes in a closed fluid system are transmitted equally to all portions of the fluid and the container's walls. In a hydraulic system, force is applied to a small piston, creating pressure. This pressure is transmitted to a larger piston, which generates a proportionally larger force, enabling the lifting of heavy objects. The system acts somewhat like a lever, magnifying the effect of moderate pressure exerted over a longer distance into powerful energy for a shorter distance. This multiplication of force is a key advantage of hydraulic systems.

What are some real-life examples of hydraulic systems in everyday machines?

Hydraulic systems use pressurized fluid to transmit power, offering flexibility, high power output for their size, and precise control. Examples of hydraulic systems in everyday machines: * Automobile brakes Hydraulic systems replaced mechanical ones in vehicles because they apply equal force to each wheel, reducing the driver's effort. * Hydraulic jacks These jacks use the principle of the hydraulic press to lift heavy objects. * Auto lifts These hydraulic machines hoist vehicles for servicing. * Hydraulic elevators Elevators can be operated by the weight or pressure of water. * Dump trucks Hydraulic lifts allow the driver to lift the truck bed.

hydraulics

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Images

Close-up of chrome-plated hydraulic piston shafts and yellow cylinders on heavy machinery, with black hoses attached to the pistons.

A diagram illustrating Pascal's principle in hydraulics shows a small piston on the left applying force to a fluid, which is transmitted to a larger piston on the right lifting a car. The diagram labels the areas, forces, and equations demonstrating how a small force on a small area creates a larger force on a larger area.

$Diagram illustrating the hydraulic fracturing process for shale gas extraction, showing a drilling rig, underground well casings, fracking fluid injection, horizontal drilling in shale, and surface equipment for separating gas and fluids. Insets highlight the well structure, fluid injection into shale, and gas flow pathways.$

At a Glance

hydraulics summary

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Key People:: Osborne Reynolds; Henri-Émile Bazin; Paolo Frisi; Domenico Guglielmini

Related Topics:: mechanics; fluid mechanics; fluid; necrobotics

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Top Questions

What is fluid mechanics?
Fluid mechanics is a branch of physics that studies how fluids respond to forces. It's a part of classical physics with important uses in hydraulic and aeronautical engineering, chemical engineering, meteorology, and zoology. Hydraulics is a branch of science that deals with practical uses of fluids, mostly liquids, in motion and is related to fluid mechanics, which gives it its theoretical basis.
3 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
What does the term 'hydraulics' mean?
Hydraulics is a science focused on the practical uses of fluids, mostly liquids, in motion. It's linked to fluid mechanics, which gives it a theoretical base. Hydraulics looks at how liquids flow in pipes, rivers, and channels, and how they're held in place by dams and tanks. Its rules can also apply to gases, especially when density changes are small. So, hydraulics covers things like fans, gas turbines, and pneumatic control systems. Hydraulic power systems are used in many industries, agriculture, and defense. Modern aircraft, cars, industrial machines, and machine tools use hydraulic power a lot.
3 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
How do liquids and gases behave differently in hydraulics?
In hydraulics, both liquids and gases adhere to Pascal's principle, which states that pressure changes in a closed container are transmitted equally throughout the fluid. However, they differ significantly due to their distinct properties.

Liquids, the primary fluids in hydraulics, are nearly incompressible, providing efficient power transmission. Hydraulic fluids, such as oil or glycerol, have low viscosity and are used in hydraulically operated mechanisms like brake cylinders.

Gases, on the other hand, are highly compressible. While they can be used in pneumatic systems, which often employ compressed air to power tools and devices, their compressibility makes them less suitable for hydraulic applications requiring precise and immediate force transmission. Gases have lower viscosity and greater compressibility than liquids, resulting in lower film thicknesses and load capacities.
5 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
What is pressure in a fluid, and how is it measured?
In fluid mechanics, pressure in a fluid is the perpendicular force exerted per unit area within the fluid. In a fluid at rest, this pressure acts equally in all directions, a principle known as Pascal's law.

Pressure is measured using instruments like pressure gauges. Common types include U-tube manometers for static pressures and Bourdon-tube gauges for higher pressures in liquids and gases. These gauges measure the difference between two pressures, known as the gauge pressure.
5 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
How does hydraulics make it possible to lift heavy objects with little force?
Hydraulics makes lifting heavy objects with little force possible through Pascal's principle. This principle states that pressure changes in a closed fluid system are transmitted equally to all portions of the fluid and the container's walls.

In a hydraulic system, force is applied to a small piston, creating pressure. This pressure is transmitted to a larger piston, which generates a proportionally larger force, enabling the lifting of heavy objects. The system acts somewhat like a lever, magnifying the effect of moderate pressure exerted over a longer distance into powerful energy for a shorter distance. This multiplication of force is a key advantage of hydraulic systems.
3 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
What are some real-life examples of hydraulic systems in everyday machines?
Hydraulic systems use pressurized fluid to transmit power, offering flexibility, high power output for their size, and precise control.

Examples of hydraulic systems in everyday machines:
* Automobile brakes Hydraulic systems replaced mechanical ones in vehicles because they apply equal force to each wheel, reducing the driver's effort.
* Hydraulic jacks These jacks use the principle of the hydraulic press to lift heavy objects.
* Auto lifts These hydraulic machines hoist vehicles for servicing.
* Hydraulic elevators Elevators can be operated by the weight or pressure of water.
* Dump trucks Hydraulic lifts allow the driver to lift the truck bed.
4 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

hydraulics, branch of science concerned with the practical applications of fluids, primarily liquids, in motion. It is related to fluid mechanics, which in large part provides its theoretical foundation. Hydraulics deals with such matters as the flow of liquids in pipes, rivers, and channels and their confinement by dams and tanks. Some of its principles apply also to gases, usually in cases in which variations in density are relatively small. Consequently, the scope of hydraulics extends to such mechanical devices as fans and gas turbines and to pneumatic control systems.

Liquids in motion or under pressure did useful work for humanity for many centuries before French scientist-philosopher Blaise Pascal and Swiss physicist Daniel Bernoulli formulated the laws on which modern hydraulic power technology is based. Pascal’s principle, formulated about 1650, states that pressure in a liquid is transmitted equally in all directions; i.e, when water is made to fill a closed container, the application of pressure at any point will be transmitted to all sides of the container. In the hydraulic press, Pascal’s principle is used to gain an increase in force; a small force applied to a small piston in a small cylinder is transmitted through a tube to a large cylinder, where it presses equally against all sides of the cylinder, including the large piston.

Bernoulli’s theorem, formulated about a century later, states that energy in a fluid is due to elevation, motion, and pressure, and if there are no losses due to friction and no work done, the sum of the energies remains constant. Thus, kinetic energy, deriving from motion, can be partly converted to pressure energy by enlarging the cross section of a pipe, which slows down the flow but increases the area against which the fluid is pressing.

Until the 19th century it was not possible to develop velocities and pressures much greater than those provided by nature, but the invention of pumps brought a vast potential for application of the discoveries of Pascal and Bernoulli. In 1882 the city of London built a hydraulic system that delivered pressurized water through street mains to drive machinery in factories. In 1906 an important advance in hydraulic techniques was made when an oil hydraulic system was installed to raise and control the guns of the USS Virginia. In the 1920s, self-contained hydraulic units consisting of a pump, controls, and motor were developed, opening the way to applications in machine tools, automobiles, farm equipment, earth-moving machinery, locomotives, ships, airplanes, and spacecraft.

In hydraulic power systems there are five elements: the driver, the pump, the control valves, the motor, and the load. The driver may be an electric motor or an engine of any type. The pump acts mainly to increase pressure. The motor may be a counterpart of the pump, transforming hydraulic input into mechanical output. Motors may produce either rotary or reciprocating motion in the load.

In the operation and control of machine tools, farm machinery, construction machinery, and mining machinery, fluid power can compete successfully with mechanical and electrical systems (see fluidics). Its chief advantages are flexibility and the ability to multiply forces efficiently; it also provides fast and accurate response to controls.

Diagram illustrating the hydraulic fracturing process for shale gas extraction, showing a drilling rig, underground well casings, fracking fluid injection, horizontal drilling in shale, and surface equipment for separating gas and fluids. Insets highlight the well structure, fluid injection into shale, and gas flow pathways. — FrackingThree steps in the extraction of shale gas: drilling a borehole into the shale formation and lining it with pipe casing; fracking, or fracturing, the shale by injecting fluid under pressure; and producing gas that flows up the borehole, frequently accompanied by liquids.

Hydraulic power systems have become one of the major energy-transmission technologies used by all phases of industrial, agricultural, and defense activity. Modern aircraft, for example, use hydraulic systems to activate their controls and to operate landing gears and brakes. Virtually all missiles, as well as their ground-support equipment, use fluid power. Automobiles use hydraulic power systems in their transmissions, brakes, and steering mechanisms. Mass production and its offspring, automation, in many industries have their foundations in the use of fluid power systems. Hydraulic fracturing, better known as fracking, has allowed the extraction of natural gas and petroleum from previously inaccessible deposits.