ernoulli's equation

Gauge vs. absolute

spring loaded pressure gauge

Variation of pressure in dneph if your ears have ever popped on a plane flight or ached during a deep dive in a swimming pool, you have experienced the effect of depth on pressure in a fluid. At the Earth’s surface, the air pressure exerted on you is a result of the weight of air above you. This pressure is reduced as you climb up in altitude and the weight of air above you decreases. Under water, the pressure exerted on you increases with increasing depth. In this case, the pressure being exerted upon you is a result of both the weight of water above you and that of the atmosphere above you. You may notice an air pressure change on an elevator ride that transports you many stories, but you need only dive a meter or so below the surface of a pool to feel a pressure increase. The difference is that water is much denser than air, about 775 times as dense. P=hρg represents the pressure due to the weight of any fluid of average density ρ at any depth h below its surface. For liquids, which are nearly incompressible, this equation holds to great depths. For gases, which are quite compressible, one can apply this equation as long as the density changes are small over the depth considered.

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Pressure measurement Many techniques have been developed for the measurement of pressure and vacuum. Instruments used to measure pressure are calledpressure gauges or vacuum gauges.

A manometer is an instrument that uses a column of liquid to measure pressure, although the term is often used nowadays to mean anypressure measuring instrument.

A vacuum gauge is used to measure the pressure in a vacuum—which is further divided into two subcategories, high and low vacuum (and sometimes ultra-high vacuum). The applicable pressure range of many of the techniques used to measure vacuums have an overlap. Hence, by combining several different types of gauge, it is possible to measure system pressure continuously from 10 mbar down to 10−11 mbar.

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32) When an object is placed in a fluid, the fluid exerts an upward force we call the buoyant force. The buoyant force comes from the pressure exerted on the object by the fluid. Because the pressure increases as the depth increases, the pressure on the bottom of an object is always larger than the force on the top - hence the net upward force. The behavior of an object submerged in a fluid is governed by Archimedes' Principle. Archimedes (a greek mathematician) determined that a body which is completely or partially submerged in a fluid experiences an upward force called the Buoyant Force, B , which is equal in magnitude to the weight of the fluid displaced by the object. This principle can be used to explain why ships, loaded with millions of kilograms of cargo, are able to float.

33) Fluid dynamics is the study of how fluids behave when they're in motion. This can get very complicated, so we'll focus on one simple case, but we should briefly mention the different categories of fluid flow.Fluids can flow steadily, or be turbulent. In steady flow, the fluid passing a given point maintains a steady velocity. For turbulent flow, the speed and or the direction of the flow varies. In steady flow, the motion can be represented with streamlines showing the direction the water flows in different areas. The density of the streamlines increases as the velocity increases.Fluids can be compressible or incompressible. This is the big difference between liquids and gases, because liquids are generally incompressible, meaning that they don't change volume much in response to a pressure change; gases are compressible, and will change volume in response to a change in pressure.Fluid can be viscous (pours slowly) or non-viscous (pours easily).Fluid flow can be rotational or irrotational. Irrotational means it travels in straight lines; rotational means it swirls.For most of the rest of the chapter, we'll focus on irrotational, incompressible, steady streamline non-viscous flow.

ernoulli's equation

The pressure, speed, and height (y) at two points in a steady-flowing, non-viscous, incompressible fluid are related by the equation:

Some of these terms probably look familiar...the second term on each side looks something like kinetic energy, and the third term looks a lot like gravitational potential energy. If the equation was multiplied through by the volume, the density could be replaced by mass, and the pressure could be replaced by force x distance, which is work. Looked at in that way, the equation makes sense: the difference in pressure does work, which can be used to change the kinetic energy and/or the potential energy of the fluid.

34) Oscillating motion is a motion that repeats itself in a regular cycle for example a sine wave or pendulum. The time taken for an oscillation to occur is often referred to as the oscillatory period. Oscillations occur not only in physical systems but also in biological systems.

Date: 2015-12-24; view: 898