Physics
Physical Quantities
Physical quantities are measurable properties of physical systems, such as length, mass, time, and temperature. They are characterized by a numerical value and a unit of measurement. In physics, these quantities are essential for describing and understanding the behavior of natural phenomena and are often used in mathematical equations to represent physical laws and relationships.
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7 Key excerpts on "Physical Quantities"
eBook - PDF- Nelson Bolívar(Author)
- 2020(Publication Date)
- Arcler Press(Publisher)
In the second part of this chapter physics, dealing with kinematics of the point-like particle, the study of the motion of particle, independently of its reasons will be described. The concepts of acceleration, velocity, and angular velocity will be outlined. These are all vector quantities, generally depending on time (Alexander, 1920; Rynasiewicz, 1995; Cremers and Soatto, 2003). 3.2. MEASUREMENT OF THE PHYSICAL QUANTI-TIES Physics provides a quantitative description of natural phenomena. Measurement of appropriate Physical Quantities leads to the discovery of Space, Time, and Motion 45 physical laws, which are the mathematical relations between those quantities (Whitney, 1968; Niu et al., 1976; Valassi, 2003). All-natural phenomena occur in space and have the temporal duration; few of them occur before, others afterward. Consequently, time and space are fundamental concepts. Physical objects are usually characterized by quantities like area, length, volume, mass, color, hardness, temperature, etc. All these concepts result from the common experience and are proper of the common language (Einstein et al., 1935; Busch, 1991). However, Physics should give a rigorous definition to every quantity, to be able to provide its numerical values. In this process of definition, the concept might become moderately different from the common language (Mäntylä and Koponen, 2007; Woodard and Taylor, 2007). For instance, consider the length of the object or distance between the two places. If one wants to designate the number one must first define the unit of length. Indeed, one will say: “That bar is five-meter long,” or, if one is in England: “That city is twenty miles away.” The measure of length of the object is ratio amongst its length and length of another object one has chosen as the unit. “A bar is five-meter long,” means that the length of bar is equal to the five one-meter long rules in the line (Cassinelli and Lahti, 1989; Liehr et al., 2017).
eBook - PDFIntroduction to Physics
Mechanics, Hydrodynamics Thermodynamics
- P. Frauenfelder, P. Huber(Authors)
- 2013(Publication Date)
- Pergamon(Publisher)
I N T R O D U C T I O N 5 4. QUANTITIES, MAGNITUDES, UNITS, AND DIMENSIONS Algebra deals exclusively with pure numbers, such as a, b, x, y, etc. The symbol a represents an arbitrary number, it is an expression signifying the addition of a definite number of ones, or units. Physics, on the other hand, is concerned with quantities. Examples of Physical Quantities are: mass, m; time, t; temperature, Γ; velocity, v; displacement, s; force, F; stress, a; torque, M. DEFINITION. A physical quantity is the product of a pure number (magni-tude) and the unit of that quantity. The magnitude specifies the number of units present in the quantity. Equations between magnitudes are called scalar equations and obey algebraic relations. The actual Physical Quantities themselves also obey equations, but these are not necessarily algebraic. A quantity can be measured in different units of the same kind; e.g., time in seconds, minutes, hours, or days; and length in centimeters, meters, or kilometers. Relations exist between different units of the same kind, e.g., 1 hr = 3600 sec, 1 km = 10 3 m = 10 5 cm, 1 km/hr = 1000 m/3600 sec = 0.278 m/sec If we wish to avoid equations between units, then we must agree at the outset which units will characterize the fundamental quantities of length, time, and mass. In this way, we clearly define a system of measurement. There are three systems of measurement currently used in physics: (1) The centimeter-gram-second system (cgs), in which the unit of length is the centimeter (cm), the unit of mass is the gram mass (gm), and the unit of time is the second (sec). (Units for the remaining Physical Quantities can then be expressed in terms of these three fundamental units.) (2) The Giorgi system (mks), in which the unit of length is the meter (m), the unit of mass is the kilogram-mass (kgm), and the unit of time is the second (sec).
eBook - PDF- Robert Resnick, David Halliday, Kenneth S. Krane(Authors)
- 2016(Publication Date)
- Wiley(Publisher)
1 MEASUREMENT D espite the mathematical beauty of some of its most complex and abstract theories, physics is above all an experimental science. It is therefore critical that those who make precise measurements be able to agree on standards in which to express the results of those measurements, so that they can be communicated from one laboratory to another and verified. In this chapter we begin our study of physics by introducing some of the basic units of physical quanti- ties and the standards that have been accepted for their measurement. We consider the proper way to ex- press the results of calculations and measurements, including the appropriate dimensions and number of significant figures. We discuss and illustrate the importance of paying attention to the dimensions of the quantities that appear in our equations. Later in the text, other basic units and many derived units are in- troduced as they are needed. 1-1 Physical Quantities, STANDARDS, AND UNITS The laws of physics are expressed in terms of many differ- ent quantities: mass, length, time, force, speed, density, re- sistance, temperature, luminous intensity, magnetic field strength, and many more. Each of these terms has a precise meaning, and they form part of the common language that physicists and other scientists use to communicate with one another — when a physicist uses a term such as “kinetic en- ergy,” all other physicists will immediately understand what is meant. Each of these terms also represents a quantity that can be measured in the laboratory, and just as there must be agreement on the meaning of these terms, there must also be agreement about the units used to express their values. Without such agreement, it would not be possible for scien- tists to communicate their results to one another or to com- pare the results of experiments from different laboratories. Such comparisons require the development and accep- tance of a set of standards for units of measurement.
eBook - PDF- A. Boros(Author)
- 2012(Publication Date)
- North Holland(Publisher)
PART I BASIC CONCEPTS This page intentionally left blank 1. Physical Quantities, UNITS, THE SI SYSTEM The measurable properties and characteristics of physical phenomena, physical processes and/or states are called Physical Quantities. Physical Quantities can be defined as the product of their measures and units. Be-fore standardization, the units to be specified in the standard may be arbitrarily chosen (preferably in a way that is easiest to reproduce) while their number provides information about the magnitude of the examined (measured, read) quantity, i.e. what fraction it is of the chosen unit, or how many times greater. In building up systems of units for the most important or the most frequently used Physical Quantities, the units are arbitrarily chosen. These are called basic units, from which the so-called derived units are then formed. In all this, coherence is an important criterion. The reader will meet the concept of coherence later in this chapter. The multiples and fractions of the basic and derived units are formed by prefixes.* Considerable efforts are being devoted worldwide to the introduction of the inter-nationally standardised system of units into general practice. This system has become known as the SI from the French term Systeme International des Unites. Table 1.1 shows the basic units of the SI system, Table 1.2 its supplementary units. TABLE 1.1. Basic quantities and basic units of the SI system Basic quantity Basic unit, symbol Length metre, m Mass kilogram, kg Time second, s Electric current ampere, A Thermodynamic temperature kelvin, Κ Luminous intensity candela, cd Amount of substance mole, mol * The prefixes are multiplying factors, the power of 10 concerned. For the prefixes of SI see Table 1 .3. 5
eBook - PDF- David Halliday, Robert Resnick, Jearl Walker(Authors)
- 2020(Publication Date)
- Wiley(Publisher)
1 C H A P T E R 1 Measurement 1-1 MEASURING THINGS, INCLUDING LENGTHS Learning Objectives After reading this module, you should be able to . . . 1.01 Identify the base quantities in the SI system. 1.02 Name the most frequently used prefixes for SI units. 1.03 Change units (here for length, area, and volume) by using chain-link conversions. 1.04 Explain that the meter is defined in terms of the speed of light in vacuum. What Is Physics? Science and engineering are based on measurements and comparisons. Thus, we need rules about how things are measured and compared, and we need experiments to establish the units for those measurements and comparisons. One purpose of physics (and engineering) is to design and conduct those experiments. For example, physicists strive to develop clocks of extreme accuracy so that any time or time interval can be precisely determined and compared. You may wonder whether such accuracy is actually needed or worth the effort. Here is one example of the worth: Without clocks of extreme accuracy, the Global Positioning System (GPS) that is now vital to worldwide navigation would be useless. Measuring Things We discover physics by learning how to measure the quantities involved in physics. Among these quantities are length, time, mass, temperature, pressure, and electric current. We measure each physical quantity in its own units, by comparison with a standard. The unit is a unique name we assign to measures of that quantity—for example, meter (m) for the quantity length. The standard corresponds to exactly 1.0 unit of the quantity. As you will see, the standard for length, which corresponds Key Ideas ● Physics is based on measurement of physical quanti- ties. Certain Physical Quantities have been chosen as base quantities (such as length, time, and mass); each has been defined in terms of a standard and given a unit of measure (such as meter, second, and kilogram).
eBook - PDF- Paul Regtien, F. van der Heijden, M. J. Korsten, W Otthius(Authors)
- 2004(Publication Date)
- Butterworth-Heinemann(Publisher)
Chapter 2 Basics of Measurement In this chapter we discuss various basic aspects of measurement science. First, the system of units is presented, and how this system has been developed from its introduction in 1795 to the present time with basically seven standard units. The materialization of a unit quantity is the next issue to be discussed. It will be shown that at present all standards (except for the kilogram) are related to funda- mental physical constants. Obviously, there are many more quantities than those seven basic quantities. In the third section we give an overview of the most import- ant quantities and properties, used in various physical domains: the geometric, electrical, thermal, mechanical, and optical domain. Relations between quantities from different domains that are fundamental to the measurement of non-electrical quantities and parameters are also given. Finally, some general aspects of sensors, the devices that convert information from one domain to another, are discussed. 2.1. System of units A unit is a particular physical quantity, defined and adopted by convention, with which other particular quantities of the same kind are compared to express their value. The value of a physical quantity is the quantitative expression of a particular physical quantity as the product of a number and a unit, the number being its numerical value. For example, the circumference of the earth around the equator is given by: Ce = 40,074.103 m (2.1) where Ce is the physical quantity and the number 40,074. 103 is the numerical value of this quantity expressed in the unit meter. Obviously, the numerical value of a particular physical quantity depends on the unit in which it is expressed. Therefore, to any measurement result the unit in which it is expressed should be added explicitly. To avoid misinterpretations the use of the international system of units (Systrme International d'unitrs, SI) is highly recommended when presenting measurement results.
eBook - PDF- Alan S. Morris(Author)
- 2001(Publication Date)
- Butterworth-Heinemann(Publisher)
In a similar fashion, standard units for the measurement of other Physical Quantities have been defined and progressively improved over the years. The latest standards for defining the units used for measuring a range of physical variables are given in Table 1.1. The early establishment of standards for the measurement of Physical Quantities proceeded in several countries at broadly parallel times, and in consequence, several sets of units emerged for measuring the same physical variable. For instance, length can be measured in yards, metres, or several other units. Apart from the major units of length, subdivisions of standard units exist such as feet, inches, centimetres and millimetres, with a fixed relationship between each fundamental unit and its sub-divisions. Table 1.1 Definitions of standard units Physical quantity Standard unit Definition Length metre The length of path travelled by light in an interval of 1/299 792 458 seconds Mass kilogram The mass of a platinum–iridium cylinder kept in the International Bureau of Weights and Measures, S` evres, Paris Time second 9 . 192631770 ð 10 9 cycles of radiation from vaporized caesium-133 (an accuracy of 1 in 10 12 or 1 second in 36 000 years) Temperature kelvin The temperature difference between absolute zero and the triple point of water is defined as 273.16 kelvin Current ampere One ampere is the current flowing through two infinitely long parallel conductors of negligible cross-section placed 1 metre apart in a vacuum and producing a force of 2 ð 10 7 newtons per metre length of conductor Luminous intensity candela One candela is the luminous intensity in a given direction from a source emitting monochromatic radiation at a frequency of 540 terahertz (Hz ð 10 12 ) and with a radiant density in that direction of 1.4641 mW/steradian.
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