![]() As with a barometer, the distance between the liquid levels in the two arms of the tube ( h in the diagram) is proportional to the pressure of the gas in the container. A closed-end manometer is a U-shaped tube with one closed arm, one arm that connects to the gas to be measured, and a nonvolatile liquid (usually mercury) in between. Show Answerġ0.3 mĪ manometer is a device similar to a barometer that can be used to measure the pressure of a gas trapped in a container. The density of water at this temperature is 1.0 g/cm 3. Where h is the height of the fluid, ρ is the density of the fluid, and g is acceleration due to gravity.Ĭalculate the height of a column of water at 25 ☌ that corresponds to normal atmospheric pressure. ![]() The pressure exerted by a fluid due to gravity is known as hydrostatic pressure, p: The torr was originally intended to be a unit equal to one millimeter of mercury, but it no longer corresponds exactly. Standard atmospheric pressure of 1 atm at sea level (101,325 Pa) corresponds to a column of mercury that is about 760 mm (29.92 in.) high. Because mercury (Hg) is about 13.6-times denser than water, a mercury barometer only needs to be as tall as a water barometer-a more suitable size. If the liquid is water, normal atmospheric pressure will support a column of water over 10 meters high, which is rather inconvenient for making (and reading) a barometer. Using very dense liquid mercury (left) permits the construction of reasonably sized barometers, whereas using water (right) would require a barometer more than 30 feet tall. In a barometer, the height, h, of the column of liquid is used as a measurement of the air pressure. Named after Evangelista Torricelli, inventor of the barometerįigure 3. Used by aviation industry, also some weather reports Table 1 provides some information on these and a few other common units for pressure measurements Table 1. Pressure can also be measured using the unit atmosphere (atm), which originally represented the average sea level air pressure at the approximate latitude of Paris (45°). In the United States, pressure is often measured in pounds of force on an area of one square inch- pounds per square inch (psi)-for example, in car tires. One pascal is a small pressure in many cases, it is more convenient to use units of kilopascal (1 kPa = 1000 Pa) or bar (1 bar = 100,000 Pa). The SI unit of pressure is the pascal (Pa), with 1 Pa = 1 N/m 2, where N is the newton, a unit of force defined as 1 kg m/s 2. (credit a: modification of work by Guido da Rozze credit b: modification of work by Ryosuke Yagi) ![]() Although (a) an elephant’s weight is large, creating a very large force on the ground, (b) the figure skater exerts a much higher pressure on the ice due to the small surface area of her skates. On the other hand, if the skater removes her skates and stands with bare feet (or regular footwear) on the ice, the larger area over which her weight is applied greatly reduces the pressure exerted:įigure 2. The figure skater weighs about 120 lbs, supported on two skate blades, each with an area of about 2 in 2, so the pressure exerted by each blade is about 30 lb/in 2:Įven though the elephant is more than one hundred-times heavier than the skater, it exerts less than one-half of the pressure and would therefore be less likely to fall though thin ice. Let’s apply this concept to determine which would be more likely to fall through thin ice in Figure 2-the elephant or the figure skater? A large African elephant can weigh 7 tons, supported on four feet, each with a diameter of about 1.5 ft (footprint area of 250 in 2), so the pressure exerted by each foot is about 14 lb/in 2: Thus, pressure can be increased either by increasing the amount of force or by decreasing the area over which it is applied pressure can be decreased by decreasing the force or increasing the area. In general, pressure is defined as the force exerted on a given area: Note that pressure is directly proportional to force and inversely proportional to area. If you actually perch a bowling ball on your thumbnail, the pressure experienced is twice the usual pressure, and the sensation is unpleasant. These may seem like huge amounts, and they are, but life on earth has evolved under such atmospheric pressure. At sea level, this pressure is roughly the same as that exerted by a full-grown African elephant standing on a doormat, or a typical bowling ball resting on your thumbnail. You can view it online here: Ītmospheric pressure is caused by the weight of the column of air molecules in the atmosphere above an object, such as the tanker car. ![]() \)Ī YouTube element has been excluded from this version of the text.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |