![]() The weight of the element itself is also shown in the free-body diagram. The forces acting upon the element are due to the pressures p( y) above and p(y+\Delta y) below it. Let the element have a cross-sectional area A and height \Delta y. Imagine a thin element of fluid at a depth h, as shown in Figure. Therefore, the pressure calculated at a given depth is different than the pressure calculated using a constant density. Fluid located at deeper levels is subjected to more force than fluid nearer to the surface due to the weight of the fluid above it. To derive a formula for the variation of pressure with depth in a tank containing a fluid of density ρ on the surface of Earth, we must start with the assumption that the density of the fluid is not constant. The density of the air begins to change significantly just a short distance above Earth’s surface. ![]() Traveling up in the atmosphere is quite a different situation, however. In a swimming pool, for example, the density is approximately constant, and the water at the bottom is compressed very little by the weight of the water on top. This is a reasonable approximation for liquids like water, where large forces are required to compress the liquid or change the volume. In the above examples, we assumed density to be constant and the average density of the fluid to be a good representation of the density. As discussed, pressure in a fluid near Earth varies with depth due to the weight of fluid above a particular level. The pressure at any point in a static fluid depends only on the depth at that point. 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. You can make ads in the Engineering ToolBox more useful to you Densities, molecular weight and chemical formulas of some common gases can be found in the table below: 1) NTP - Normal Temperature and Pressure - is defined as 20oC (293.15 K, 68oF) and 1 atm ( 101.325 kN/m2, 101.325 kPa, 14.7 psia, 0 psig, 30 in Hg, 760 torr) 2) STP - Standard. 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. The elevations of water surfaces hold important information on the earths oceans and land surface waters. 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. A metallic sphere floats in an immiscible mixture of water (density 10 3 kg/m 3) and a liquid (density 8×103kg/m3) such that its ( 2 3) part is in water and ( 1 3) part in the liquid. 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. Thus, the units of density are defined by the base units of mass and length.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. We use the mass and volume of a substance to determine its density. Learn about the various temperature scales that are commonly used in chemistry.Calculate density from experimental results.By the end of this section, you will be able to:
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |