Density

9 Key excerpts on "Density"

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  eBook - ePub

  Practical Handbook of Physical Properties of Rocks and Minerals (1988)

  • Robert S. Carmichael(Author)
  • 2017(Publication Date)
  • CRC Press

    (Publisher)

  Section IIDensities of Rocks and Minerals ByGary R. Olhoeft and Gordon R. Johnson

  Concepts

  Density is a physical property that changes significantly among various rock types owing to differences in mineralogy and porosity. If the distribution of underground rock densities is known, potentially much information can be learned about subsurface geology. Laboratory or borehole measurements of Density can thus aid in the interpretation of field studies and, especially, gravity surveys.

  In common usage, Density is defined as the weight in air of a unit volume of an object at a specific temperature; however, in strict usage, the Density of an object is defined as mass per unit volume. Weight is defined as the force that gravitation exerts on a body and thus varies with location, whereas mass is a fundamental property, a measure of the matter in a body; and mass is constant irrespective of geographic location, altitude, or barometric pressure. In many instances, such as routine Density measurements of rocks, the sample weights are considered to be equivalent to their masses because the discrepancy between weight and mass will result in less error in the computed Density than will experimental errors encountered in the measurement of volume. Therefore, Density is often determined using weight rather than mass. Moreover, when using an equal-arm balance and standard masses to weigh an object, the effects of variations in the force of gravity are negated. The resultant measurement of apparent mass differs slightly from true mass due to the buoyant effects of air. True mass, if desired, can be computed by using a correction for the buoyant effects of air.

  Specific gravity, in contrast to Density, is defined as the ratio of the weight or mass in air of a unit volume of material at a stated temperature to the weight or mass in air of a unit volume gas-free distilled water at a stated temperature. Density should be reported in SI units (kg/m3 ) but often is reported as g/cm3 . Specific gravity is dimensionless. Measurements of weight and volume are usually made in laboratories where normally minor variations of ambient temperature in the same laboratory as well as among laboratories have little effect on densities of rocks and minerals. For this reason the temperature at which Density or specific gravity is determined is often ignored, and densities are thus commonly reported without regard to temperature. However, according to Mason,1 ignoring the effect of temperature on determinations of Density can lead to errors that are greater than the experimental error encountered while making careful routine measurements. Mason1 discussed the concept of Density in relation to temperature, errors to expect from misunderstanding of the effects of temperature, and how to apply corrections in order to minimize errors. For the sake of clarity, the expression for Density should be “Density at x” where x is the temperature of the material. The usage of the terms Density and specific gravity are standardized in a few publications such as International Society for Rock Mechanics Committee on Laboratory Tests, Document number 2,2 and ASTM E12-70.3

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  Applied Mathematics

  Made Simple

  • Patrick Murphy(Author)
  • 2014(Publication Date)
  • Butterworth-Heinemann

    (Publisher)

  DEFINITION : The Density of a body is the mass of a unit volume of the body. The basic SI units of mass and volume are the kilogramme and cubic metre. It follows therefore that the basic SI unit of Density is the kilogramme Hydrostatics I: Density, Relative Density, and Buoyancy 259 per cubic metre, abbreviated to kg m ~ 3 . To put this in the form of an equation we have Mass of the substance Density of a substance = Volume of the substance Thus, if 3 kg of a substance has a volume of 0-004 m 3 , the Density of the sub-stance is 3 0 0 0 4 = 750 kg na-if the volume is given in cubic millimetres or cubic centimetres the expression of Density in SI units occasions no difficulty since the required arithmetic is elementary. For example, suppose 20 g of a substance has a volume expressed in the older but more convenient units of 5 cm 3 : then the Density is simply 0 0 2 0 kg 0 02 . _ 3 A N G V X % _ 3 5 x ( 0 0 1 ) 3 m 3 = 5 x 0 0 1 x 0 01 x 0 0 1 k gm 3 = 4 0 0 ° k g m Thus 4 g c m ~ 3 becomes 4000 kg m 3 , and similarly 7 1 g c m 3 would become 7100 kg m 3 , so the conversion is a simple one to perform. The measure-ment of volume in cubic metres is very inconvenient in actual laboratory work, so we shall express volumes in cubic centimetres whenever the practical nature of an example makes this necessary. Densities of Common Substances k g m -3 Water (at 4 °C) = 1 000 Sea-water = 1024 Aluminium = 2 710 Copper 8 930 Gold 19 320 Iron = 7 860 Lead = 11 370 Mercury 13 600 Silver = 10 500 Tin = 7 290 Cork = 220-260 Methylated spirit 830 Turpentine = 870 Zinc = 7 100 The Density of a solid body varies very little. But with gases the influence of pressure and temperature is very great, and we shall discuss the effects of this later. Since most liquids and bodies expand when the temperature is raised, it follows that temperature will influence volume and thereby Density.

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  Introduction to Physics

  • John D. Cutnell, Kenneth W. Johnson, David Young, Shane Stadler(Authors)
  • 2015(Publication Date)
  • Wiley

    (Publisher)

  11.1 | Mass Density Fluids are materials that can flow, and they include both gases and liquids. Air is the most common gas and flows from place to place as wind. Water is the most familiar liquid, and flowing water has many uses, from generating hydroelectric power to white-water rafting. The mass Density of a liquid or gas is one of the important factors that determine its be- havior as a fluid. As indicated below, the mass Density is the mass per unit volume and is denoted by the Greek letter rho (r). Definition of Mass Density The mass Density r is the mass m of a substance divided by its volume V: r 5 m V (11.1) SI Unit of Mass Density: kg/m 3 Equal volumes of different substances generally have different masses, so the Density depends on the nature of the material, as Table 11.1 indicates. Gases have the smallest den- sities because gas molecules are relatively far apart and a gas contains a large fraction of empty space. In contrast, the molecules are much more tightly packed in liquids and solids, and the tighter packing leads to larger densities. The densities of gases are very sensitive to changes in temperature and pressure. However, for the range of temperatures and pressures encountered in this text, the densities of liquids and solids do not differ much from the values in Table 11.1. It is the mass of a substance, not its weight, that enters into the definition of Density. In situations where weight is needed, it can be calculated from the mass Density, the volume, and the acceleration due to gravity, as Example 1 illustrates. The air is a fluid, and this chapter examines the forces and pressures that fluids exert when they are at rest and when they are in motion. In a tornado the air is moving very rapidly, and as we will see, moving air has a lower pressure than stationary air. This difference in air pressure is one of the reasons that tornadoes, such as the one in this photograph, are so destructive.

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  The Characterization of Chemical Purity

  Organic Compounds

  • L. A. K. Staveley(Author)
  • 2016(Publication Date)
  • Butterworth-Heinemann

    (Publisher)

  Density MEASUREMENTS TOMASZ PLEBANSKI Division of Physico-Chemical Metrology, National Board for Quality Control and Measures (CUJiM), Warsaw, Poland 1. INTRODUCTION Specific mass, p (t, p), commonly called Density, is a strictly defined property of physical bodies, namely the mass per unit volume at a definite temperature t and pressure p. Since this discussion will be simplified by confining it, with few exceptions, to liquids, the small influence of atmospheric pressure variations will be neglected, and the absolute Density at temperature t will be denoted p t , or simply p if it is clear that all densities under consideration are referred to the same temperature. For pure compounds p can only be predicted approximately from various semi-quantitative correlations between Density and chemical structure. We shall therefore consider Density as a quantity determined by experiment, and we shall be interested primarily in the relation between Density and the composition of the material in question. This relation may be used as a purity criterion whenever material consists of a main component and a small amount of contamination. Under favourable conditions, when the average Density of impurities differs from that of the main component by 0-1-1 g/cm 3 , the accuracy and sensitivity of this criterion may be as high as 10~ 2 and 10 -3 per cent by weight, respectively, provided Density differences as low as 10 -6 g/cm 3 are measurable. Generally, however, impurity concentrations which may usefully be discussed are of the order of 0*1-1 per cent by weight. The examination of purity by Density measurements is always a matter of comparison of the Density />* of the material in question with a reference Density pr) associated with a definite purity of the same material. Hence the accuracy of purity determination by this method depends very much on the critical use of reference materials and reference numerical data.

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  eBook - ePub

  Measurement and Control Basics, Fifth Edition

  • Thomas Hughes(Author)
  • 2014(Publication Date)
  • International Society of Automation

    (Publisher)

  9

  Liquid Density Measurement

  Introduction

  This chapter discusses the basic principles of liquid Density and specific gravity measurements. Control of the more common variables, such as flow, temperature, level, and pressure, is the basic criterion for process control. However, there are cases where measuring Density or specific gravity (SG) is the best way to determine and control the concentration of a process solution.

  Density, ρ , is defined as the mass per unit volume. The Density of a homogeneous fluid may depend on many factors, such as its temperature and the pressure to which it is subjected. Most liquids are only slightly compressible, and pressure effects in Density and specific gravity control applications are normally neglected. The Density of a liquid is an important characteristic that is often used to determine properties like concentration, composition, and the BTU content of some fuels, and for liquid flow and volumetric applications.

  Density Units and Definitions

  Relative Density, or specific gravity, is defined as the ratio of the Density of a fluid to that of water at a given temperature. Since specific gravity is a ratio, it has no associated units. Both Density and specific gravity express the same physical property of a material and they are only meaningful if defined at a given temperature. In the case of specific gravity, the temperature can be different for the process material and the reference liquid. This is permissible but the different temperatures must be clearly stated. A specific gravity table, for instance, might list a process fluid as having a specific gravity of 0.9580/40 . This indicates that the process fluid at 80°F (27°C) will have a Density of 0.95 times that of water at 40°F (4.4°C).

  Since Density is expressed as mass per unit volume, these units must be listed with the process data. Commonly used Density units are grams per cubic centimeter (g/cm3 ), kilograms per cubic meter (kg/m3 ) and pounds per cubic foot (lbs/ft3

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  Engineering Properties of Foods

  • M.A. Rao, Syed S.H. Rizvi, Ashim K. Datta, Jasim Ahmed, M.A. Rao, Syed S.H. Rizvi, Ashim K. Datta, Jasim Ahmed(Authors)
  • 2014(Publication Date)
  • CRC Press

    (Publisher)

  Density and porosity have a direct effect on the other physical properties. Volume change and porosity are important parameters in estimating the diffu-sion coefficient of shrinking systems. Porosity and tortuosity are used to calculate effective diffusivity during mass transfer processes. Mechanical properties of agricultural materials also vary with porosity. This chapter provides terminology, measurement techniques, and prediction models of selected mass–volume–area-related properties. 1.2 FUNDAMENTAL CONSIDERATIONS 1.2.1 Volume 1.2.1.1 Boundary Volume Boundary volume is the volume of a material considering the geometric boundary. A mate-rial’s volume can be measured by buoyancy force; liquid, gas, or solid displacement; or gas adsorption; it can also be estimated from the material’s geometric dimensions. Estimation equations of the boundary volume of shapes of regular geometry are given in Table 1.1. 1.2.1.2 Pore Volume Pore volume is the volume of the voids or air inside a material. 1.2.2 Density Density is one of the most important mechanical properties and so is widely used in pro-cess calculations. It is defined as mass per unit volume: Density Mass Volume = = m V (1.1) The SI unit of Density is kg/m 3 . In many cases foods contain multicomponent phases, such as solid, liquid, and gaseous or air. In this case, a simple definition such as that given above cannot be sufficient to relate the mass and volume. In this case, different terminol-ogy should be defined. Rahman (1995) clearly explained different forms of Density used in process calculations and characterizing food products. The definitions are given as follows. 1.2.2.1 True Density True Density ( ρ T ) is the Density of a pure substance or a composite material calculated from its components’ densities considering conservation of mass and volume.

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  Forest Products and Wood Science

  An Introduction

  • Rubin Shmulsky, P. David Jones(Authors)
  • 2018(Publication Date)
  • Wiley-Blackwell

    (Publisher)

  A piece of sugar pine with a Density of 380 kg m −3 dry wood substance m −3 includes about 25% cell wall material and 75% voids (principally lumen space) by volume. In contrast, white oak with a Density of 750 kg dry wood substance m −3 has a void volume of about 50%. When considering the Density of wood, it can be helpful to visualize the void volume to which it corresponds. It is easy to see why a block containing 50% void volume will resist crushing to a much greater extent than a block with 75% void volume. The physicomechanical properties of wood are mainly determined by three characteristics: (i) the porosity or proportion of void volume, which can be estimated by measuring the Density; (ii) the organization of the cell structure, which includes the microstructure of the cell walls and the variety and proportion of cell types (the organization of the cell structure is principally a function of species); and (iii) the moisture content. The effect of bound water on the properties of wood was discussed in Chapter 7. In the engineering and use of wood materials, it is important to keep these three characteristics in mind. Density and specific gravity are the two physical properties commonly used to describe the mass of a material per unit volume. These properties are commonly used in connection with all types of materials. Density (D) is defined as the mass or weight per unit of volume. It is usually expressed in kilograms per cubic meter (kg m −3), grams per cubic centimeter (g cm −3), or pounds per cubic foot (lb ft −3). A word of caution is in order when discussing wood Density. There is no universally accepted procedure for calculating the Density of wood. For instance, although Density is frequently expressed in terms of green weight and green volume when calculating weights for transportation or construction, this is not always the case. It is, therefore, important to be sure of the basis of the calculation when discussing wood Density

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  Air and Water

  The Biology and Physics of Life's Media

  • Mark Denny(Author)
  • 2020(Publication Date)
  • Princeton University Press

    (Publisher)

  Other soft parts are less dense. Muscle has a Density of 1050 to 1080 kg m~~ 3 and guts generally have a Density of about 1040 kg m~ 3 . Body fluids (blood, hemolymph, etc.) typically have a Density of about 1010 kg m~ 3 Lipids are the only common body constituents less dense than water. Most animal fats and oils have densities of 915 to 945 kg m~ 3 . Taken as a whole, animals typically have densities between 1060 and 1090 kg m~ 3 There are exceptions, of course, and some of these are discussed later in this chapter. The Density of wood spans a broad range and is very sensitive to the volume fraction of air in the material; the more trapped air, the less dense the wood. As a result, Density varies not only from species to species, but it can also vary substantially within an individual depending on the hydration state of the plant. It is common to assume that wood is less dense than water because it floats. This need not be the case, however, and it is a safe generalization only for the wood of temperate-zone trees, where wood densities are typically 500 to 1000 kg m~~ 3 . Many tropical trees (e.g., ebony, lignum vitae) are considerably denser than water and sink if immersed. The solid part of wood (cellulose and the various substances that bind it together) has a Density of about 1500 kg m~ 3 , and this sets the upper limit to the Density of wood. 4.3 Buoyancy We begin our examination of the biological consequences of fluid Density by considering the peculiar force known as buoyancy. This is the force that suspends blimps in air and allows boats to float on water. Before we consider the conse-quences of buoyancy, it will be useful to consider its physics. We first need to examine how pressure varies with position in a fluid. For simplicity, consider a fluid whose Density is pf everywhere. We can place a circle of radius r within the fluid, with its plane perpendicular to the acceleration of gravity (fig. 4.6), and ask what forces act on its area.

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  Hegel's Philosophy of Nature

  Volume II Edited by M J Petry

  • G W F Hegel(Author)
  • 2014(Publication Date)
  • Taylor & Francis

    (Publisher)

  10 of its mass. Physics attempts to explain Density in its own way, by assuming certain propositions, i.e. (1) That given an equal number of material parts of equal size, there will be no difference in weight. From this it follows (2) that it is the measure of the number of parts which determines 15 the weight. It also determines the space, so that (3) two entities of equal weight also fill the same amount of space. Consequently, (4) when two entities of equal weight have different volumes the amount of space they occupy as materials is the same, and their difference is assumed to be 20 the result of their pores. The first three propositions make it necessary to postulate the pores in the fourth. These propositions are not based upon experience however, they are based merely upon the understanding and its proposition of identity. They are therefore formal apriori inventions, as the pores are. Kant has 25 already opposed intensity to the quantitative determination of amount, and posited a constant number of parts with a higher propensity for filling space, instead of more parts in an equal volume. In this way he has initiated a so-called dynamic physics. The determination of intensive quantum + would be just as valid as that of extensive quantum, although the popular conception of Density mentioned above has confined itself to the latter category. In this instance however, the determination of intensive magnitude has the advantage of implying measure, and above all of indicating a being-in-self 35 which in its Notional determination is immanent determinateness of form, and which only appears, by means of comparison, as a general quantum. Dynamic physics gets no further than regarding these differences as extensive or intensive, and so fails to express any reality (§ 103 Rem.). 40

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