At any point within a static fluid, the pressure on all sides must be equal-otherwise, the fluid at that point would react to a net force and accelerate. Pressure in a static fluid in a uniform gravitational fieldĪ static fluid is a fluid that is not in motion. The weight of the fluid is equal to its mass times the acceleration due to gravity. The pressure due to the fluid is equal to the weight of the fluid divided by the area. Plasma will not be discussed in depth in this chapter because plasma has very different properties from the three other common phases of matter, discussed in this chapter, due to the strong electrical forces between the charges.ġ\,\text) plus the pressure due to the weight of the fluid. At high temperatures, molecules may disassociate into atoms, and atoms disassociate into electrons (with negative charges) and protons (with positive charges), forming a plasma. There exists one other phase of matter, plasma, which exists at very high temperatures. In this chapter, we generally refer to both gases and liquids simply as fluids, making a distinction between them only when they behave differently. When placed in an open container, gases, unlike liquids, will escape. This makes gases relatively easy to compress and allows them to flow (which makes them fluids). In contrast, atoms in gases are separated by large distances, and the forces between atoms in a gas are therefore very weak, except when the atoms collide with one another. Because the atoms are closely packed, liquids, like solids, resist compression an extremely large force is necessary to change the volume of a liquid. When a liquid is placed in a container with no lid, it remains in the container. That is, liquids flow (so they are a type of fluid), with the molecules held together by mutual attraction. This occurs because the atoms or molecules in a liquid are free to slide about and change neighbors. Liquids deform easily when stressed and do not spring back to their original shape once a force is removed. A gas must be held in a closed container to prevent it from expanding freely and escaping. (c) Atoms in a gas move about freely and are separated by large distances. Forces between the atoms strongly resist attempts to compress the atoms. (b) Atoms in a liquid are also in close contact but can slide over one another. Other units in the category of Pressure include Atmosphere (metric) (at), Atmosphere (standard) (atm), Bar (bar), Barad (barad), Barye, CentiHg (0☌), Centimeter of Mercury (0☌) (cmHg (0 ☌)), Centimeter of Water (4☌) (cmH 2O), Dyne Per Square Centimeter (dyn/cm 2), Foot of Water (4☌) (ft H 2O), Hectopascal (hPa), Inch of Mercury (0☌) (inHg (0 ☌)), Inch of Mercury (15.56☌) (inHg (15.56 ☌)), Inch of Water (15.56☌) (inH 2O (15.56 ☌)), Inch of Water (4☌) (inH 2O (4 ☌)), Kilogram Force Per Square Centimeter (kgf/cm 2), Kilogram Force Per Square Decimeter (kgf/dm 2), Kilogram Force Per Square Meter (kgf/m 2), Kilogram Force Per Square Millimeter (kgf/mm 2), Kilopascal (kPa), Kilopound Force Per Square Inch (kip/in 2, ksi, KSI), Megapascal (MPa), Meter of Water (15.56☌) (mH 2O, mCE (15.56 ☌)), Meter of Water (4☌) (mH 2O, mCE (4 ☌)), Microbar (barye, Barrie) (µbar), Micron of Mercury (millitorr) (µHg (0 ☌)), Millibar (mbar), Millimeter of Mercury (0☌) (mmHg, torr, Torr (0 ☌)), Millimeter of Water (15.56☌) (mmH 2O, mmCE (15.56 ☌)), Millimeter of Water (4☌) (mmH 2O, mmCE (4 ☌)), Millitorr (mtorr), Newton Per Square Meter (N/m 2), Ounce Force (av.) Per Square Inch (ozf/in 2, osi), Pascal (Pa, N/m 2), Pound Force Per Square Foot (lbf/ft 2), Pound Force Per Square Inch (psi, PSI, lbf/in 2), Poundal Per Square Foot (pdl/ft 2), Poundal Per Square Inch (pdl/in 2), Standard Atmosphere (atm), Ton Force (long) Per Square Foot (tonf/ft 2 (UK)), Ton Force (long) Per Square Inch (tonf/in 2 (UK)), Ton Force (metric) Per Square Centimeter (tonf/cm 2 (metric)), Ton Force (metric) Per Square Meter (tonf/m 2 (metric)), Ton Force (short) Per Square Foot (tonf/ft 2 (US)), Ton Force (short) Per Square Inch (tonf/in 2 (US)), and Torr (torr).Figure 14.2 (a) Atoms in a solid are always in close contact with neighboring atoms, held in place by forces represented here by springs. Note that the seven base dimensions are M (Mass), L (Length), T (Time), Q (Temperature), N (Aamount of Substance), I (Electric Current), and J (Luminous Intensity).
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