Even though they're not solid, fluids such as water have the remarkable ability to perform useful work. Hydraulics, the branch of science that studies the mechanical properties of fluids, has helped people invent many uses of hydraulic devices, including brakes, lifts, compactors and other machines that make life convenient, productive and safer.
Hydraulic Lifts and Fluid Power
Blaise Pascal derived a law that explains how people can harness the power of fluids. When you apply pressure to liquid in a confined container, that pressure transmits equally to all other points in the container. According to the law, it's also possible for a hydraulic system to multiply forces. For instance, a hydraulic arm uses these principles to help you hoist thousands of pounds using your hands. You press down to apply a small force to one part of the jack's fluid, and the force multiples enough to lift a car.
You witness hydraulics in action every time you ride in a vehicle or see one pass; car braking systems are among the most common uses of hydraulic machines. A vehicle's braking system has several critical components, and one of them comes in a bottle or can. Brake fluid, a hydraulic liquid, is so important that brake systems could fail without it. When you press your foot on a brake pedal, a piston and rod in a master cylinder move. This movement exerts force on hydraulic fluid constrained inside brake lines. Because of Pascal's law, the pressure moves through the lines, presses against another cylinder and causes the vehicle's brake shoes and pads to contact the disc or drum and slow the wheels down.
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Airplanes and Hydraulic Systems
In addition to helping planes slow down on runways, hydraulic power systems manage the flaps, landing gear and flight control surfaces. Hydraulic liquids do this by transferring forces applied at one location to controls at another point on the plane. The operating pressure in an airplane's hydraulic system may vary from 200 to 5,000 psi. America's fleet of space shuttles contained hydraulic systems that could function in zero gravity and the harsh environment of space.
Liquid's Power to Compress Substances
Hydraulic trash compactors also capitalize on the fact that a small amount of pressure on a contained fluid can produce a stronger force elsewhere in the system. Before refuse gets to a landfill, garbage trucks with hydraulic arms compact the trash to make it take up less space. Compacting refuse helps save the environment and prevents landfills from filling up so quickly. Hotels, restaurants and other businesses that produce waste can harness the power of fluid mechanics by purchasing hydraulic trash compactors.
All Hydraulic Fluids are Not Alike
Viscosity, which measures a liquid's resistance to flow, is an important property of hydraulic fluid that influences a hydraulic system's efficiency. Fluids that you choose for a hydraulic system must have such a high viscosity level that it hinders flow, resulting in increased temperature and power loss.