Physics
Use of SI Units
The use of SI units in physics provides a standardized system for measuring physical quantities such as length, mass, time, and temperature. This system simplifies communication and ensures consistency in scientific measurements and calculations across different experiments and research. The SI units are based on fundamental constants of nature, making them universally applicable and reliable for scientific work.
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8 Key excerpts on "Use of SI Units"
eBook - PDF- David Halliday, Robert Resnick, Jearl Walker(Authors)
- 2018(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- David Halliday, Robert Resnick, Jearl Walker(Authors)
- 2021(Publication Date)
- Wiley(Publisher)
1 1.1 MEASURING THINGS, INCLUDING LENGTHS Learning Objectives After reading this module, you should be able to . . . 1.1.1 Identify the base quantities in the SI system. 1.1.2 Name the most frequently used prefixes for SI units. 1.1.3 Change units (here for length, area, and volume) by using chain-link conversions. 1.1.4 Explain that the meter is defined in terms of the speed of light in a vacuum. 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). Other physical quantities are defined in terms of the base quantities and their standards and units. ● The unit system emphasized in this book is the International System of Units (SI). The three physical quantities displayed in Table 1.1.1 are used in the early chapters. Standards, which must be both accessible and invariable, have been established for these base quantities by international agreement. These standards are used in all physical measurement, for both the base quantities and the quantities derived from them. Scientific notation and the prefixes of Table 1.1.2 are used to simplify measurement notation. ● Conversion of units may be performed by using chain-link conversions in which the original data are multiplied successively by conversion factors written as unity and the units are manipulated like algebraic quantities until only the desired units remain. ● The meter is defined as the distance traveled by light during a precisely specified time interval. 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.
eBook - PDFEngineering Technology NQF2 SB
TVET FIRST
- Jowaheer Consulting and Technologies Business Programme Developments(Author)
- 2013(Publication Date)
- Macmillan(Publisher)
174 Module 5: SI units of measurement Module 5 SI units of measurement In Topics 3 and 4, you looked at different tools or instruments for measuring certain values, including thermometers, speedometers, scales and voltmeters. In this topic, you are going to study more closely the International System of Units, the most widely used system of measurement in use today. Why and how do we measure things? We measure things so that we are accurate in what we say and do. As an engineering student, you will need to take measurements and perform calculations. The results will be meaningless unless they are numerically and dimensionally correct and accurate. For example, we can say that the length of the classroom is 10. Ten what? Units of measurement provide a common way of understanding the quantity we are describing. In this module, you will gain an understanding of the SI units used in engineering science. By the end of this module, you will be able to: • identify base units of measurement used in engineering science • define the physical quantities that are measured by the SI units • perform conversions according to relevant digital values • derive new units from the relationships between the SI units (i.e. the quantities they measure). Figure 5.1 International system of units Units in this module Unit 5.1 SI base units of measurement Unit 5.2 Converting SI units Unit 5.3 SI derived units of measurement 175 Module 5: SI units of measurement Unit 5.1 SI base units of measurement By the end of this unit, you will be able to: • identify basic units of measurement used in engineering science • define the physical quantities that are measured by the SI units. Different measurement systems Until 1968, South Africa used the imperial system of measurement. South Africa gradually introduced the metric system of measurement using SI units over a number of years. Finally, in 1973, the use of imperial measurements was prohibited.
eBook - PDFElectrical Principles & Practice NQF2 SB
TVET FIRST
- Jowaheer Consulting and Technologies(Author)
- 2013(Publication Date)
- Macmillan(Publisher)
2 Topic 1 SI units of measurement Module 1 SI units of measurement Overview In this topic, you are going to study more closely the International System of Units, the most widely used system of measurement today. Why and how do we measure things? We measure things so that we are accurate in what we say and do. As an engineering student, you will need to take measurements and perform calculations. The results will be meaningless unless they are numerically and dimensionally correct and accurate. For example, we can say that the length of the classroom is 10. Ten what? Units of measurement provide a common way of understanding the quantity we are describing. In this module, you will gain an understanding of the SI units used in engineering. By the end of this module, you will be able to: • identify base units of measurement used in engineering • define the physical quantities that are measured by the SI units • describe the rules when writing SI units of measurements • convert scientific notation to decimal notation and vice versa (convert answer to 3 decimal digits) • list common prefixes used in engineering • derive new units from the relationships between SI units (i.e. the quantities they measure) Range: speed, velocity, acceleration, force, weight, work, energy, torque, resistance, density, pressure and power • explain the theory and measure plane and solid angles. Figure 1.1 International System of Units Module 1 SI Units of measurement 3 ? ? ? Did you know? Units in this module Unit 1.1 SI base units of measurement Unit 1.2 Converting SI units Unit 1.3 SI derived units of measurement Unit 1.1 SI base units of measurement By the end of this unit, you will be able to: • identify base units of measurement used in engineering • define the physical quantities that are measured by SI units • describe the rules when writing SI units of measurement. Different measurement systems Until 1968, South Africa used the imperial system of measurement.
eBook - ePub- Atef Korchef(Author)
- 2022(Publication Date)
- CRC Press(Publisher)
2 Measurements
DOI: 10.1201/9781003257059-22.1 Objectives
At the end of the present chapter, the student should be able to:- Select the appropriate units in the International System of Units (known by the international abbreviation SI) of measurement.
- Differentiate between fundamental quantity and derived quantity.
- Convert units.
- Define and use the basic methods and tools of measurements, such as significant figures and rounding off.
2.2 Measurements
Measurement is the process of comparing an unknown quantity with another known quantity of the same kind to find out how many times the first includes the second.- Physical quantities are either fundamental (basic) quantities or derived quantities.
- Fundamental quantities cannot be defined in terms of other physical quantities.Examples: length, time, mass, temperature and amount of a substance.
Quantity consists of a number telling us how much, and a unit which shows what the scale of measurement is. Examples of base units in SI are given in Table 2.1 . SI base units of mass, temperature and amount of a substance (kg, K and mol, respectively) are widely used by chemists (Table 2.1 ).TABLE 2.1 Examples of SI base units
Note that:Base quantity SI base unit Name Symbol Name Symbol Length l, x, r, etc meter m Mass m kilogram kg Time t second s Temperature T Kelvin K Amount of a substance n mole mol - The SI unit of mass is kg (with small or lowercase k), not Kg (with capital K).
- The SI unit of the amount of a substance (mole) is denoted by mol (without an “e”), not mole. Also, kg is not the SI base unit for the amount of a substance but the SI unit of mass.
eBook - PDFChemistry
The Molecular Nature of Matter
- Neil D. Jespersen, Alison Hyslop(Authors)
- 2021(Publication Date)
- Wiley(Publisher)
Finally, one more change that has been standardized is how numbers are written. For large numbers and small numbers less than one with many decimal places, spaces are used to separate the numbers. For example, 9,192,631,770 Hz would be written as 9 192 631 770 Hz and 1.602176634 × 10 −19 C would be written as 1.602 176 634 × 10 −19 C. In this book, we will be using commas if we have a number that is larger than 9999 (e.g., 9,192,631,770 Hz). Furthermore, if a number is less than one and is not written in scientific notation, then a zero always precedes the decimal point (e.g., write 0.393 7 inches, not .3937 inches). 1.4 Measurement of Physical and Chemical Properties 39 In scientific measurements, all physical quantities will have units that are combinations of the seven base SI units. For example, there is no SI base unit for area, but to calculate area we multiply length by width. Therefore, the unit for area is derived by multiplying the unit for length by the unit for width. Length and width are measurements that have the SI base unit of the meter (m). length × width = area (meter) × (meter) = (meter) 2 m × m = m 2 The SI derived unit for area is therefore m 2 (read as meters squared or square meter). In deriving SI units, we employ a very important concept that we will use repeatedly throughout this book when we perform calculations: Units undergo the same kinds of math- ematical operations that numbers do. We will see how this fact can be used to convert from one unit to another in Section 1.6. EXAMPLE 1.1 Deriving SI Units Linear momentum is the term used to describe an object moving at a constant velocity in a straight line. It is equal to the object’s mass times its velocity. What is the SI derived unit for linear momentum? Analysis: To derive a unit for a quantity, first we express it in terms of simpler quantities. We’re told that linear momentum is mass times velocity.
eBook - ePubThe Reform of the International System of Units (SI)
Philosophical, Historical and Sociological Issues
- Nadine de Courtenay, Olivier Darrigol, Oliver Schlaudt(Authors)
- 2019(Publication Date)
- Routledge(Publisher)
The definition of a unit as in equation (4) or equation (5), that does not refer to the relations in the system of quantities, is independent, and dependent is instead a definition, as in equation (6), which does refer to such relations. For example, a definition of length unit based on the relation of length with time and velocity is a dependent definition.2.4 Concepts related to the realization of the definition of quantity units
The main concepts assumed related to the realization of the definition of quantity units are:- quantity realizing the definition of a unit;
- object realizing the definition of a unit;
- calibration;
- metrological traceability chain;
- calibration uncertainty.
A measurement process is based on a measurement procedure that specifies a way for comparing the measurand and the unit. This comparison implies the availability of a quantity that realizes the definition of the unit through the realization of a support of that quantity. The object realizing the definition of a unit is called a measurement standard. The comparison with a unit is then generally obtained by realizing a chain of measurement standards, from a primary one to the working standard used in measurement and calibrated against the primary standard through a metrological traceability chain. In the processes of calibration that yields the chain, a calibration uncertainty is produced that generally increases in each step of the chain from the primary standard to the standard involved in the measuring system.3 Basic criteria
The main operative target of the definition of a system of units is to provide a basis for measurement, for which quantity units are indeed essential.10
eBook - ePub- Mike Aitken, Bill Broadhurst, Stephen Hladky(Authors)
- 2009(Publication Date)
- Garland Science(Publisher)
Table 1.2 .Table 1.2 Examples of SI derived unitsderived quantityderived unitsymbolarea square meter m2volume cubic meter m3speed, velocity meter per second ms−1acceleration meter per second squared m s−2mass density kilogram per cubic meter kg m−3amount of substance concentration mole per cubic meter mol m−3mass fraction kilogram per kilogram, which may be represented by the number 1 kg kg−1 = 1mole fraction amount of substance per amount of all substances present mol mol−1 = 1per cent per cent % Some of these derived quantities are assigned special names, because it is useful to think of these combinations of units together. For instance, force is sufficiently important that it is measured in its own unit, the newton, with symbol N. However, because 1 N is defined as that force which would accelerate a 1 kg mass at 1 m s−2 ,1 N = 1 kg × 1 ms= 1 kg m− 2s,− 2(EQ1.22) the symbol N is just a synonym for kg m s−2
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