Ventilation
What is the main sign of a physical quantity. Lecture Property

What is the main sign of a physical quantity. Lecture Property

Measurement– a set of predominantly experimental operations performed using a technical means that stores a unit of quantity, allowing one to compare the measured quantity with its unit and obtain

the desired value of the quantity. This value is called the measurement result.

To establish differences in the quantitative value of the displayed object, the concept of physical quantity is introduced.

Physical quantity (PV) is one of the properties of a physical object (phenomenon, process), common in qualitative terms for many physical objects, but quantitatively individual for each object (Fig. 4.1).

For example, density, voltage, refractive index, etc.

So, using a measuring device, for example a direct current voltmeter, we measure the voltage in volts of a particular electrical circuit by comparing the position of the pointer (arrow) with the unit of electrical voltage stored on the voltmeter scale. The found voltage value as a certain number of volts represents the measurement result.

Rice. 4.1.

A distinctive feature of a quantity can be a unit of measurement, a measurement technique, a standard sample, or a combination of these.

If necessary, it is possible to measure not only a physical quantity, but also any physical and non-physical object.

If the mass of a body is 50 kg, then we are talking about the size of a physical quantity.

Size of physical quantity– quantitative determination of a physical quantity inherent in a specific material object (phenomenon, process).

True Size a physical quantity is an objective reality that does not depend on whether the corresponding characteristic of the object’s properties is measured or not. Real value physical quantity is found experimentally. It differs from the true value by the magnitude of the error.

The size of a quantity depends on which unit is used when measuring the quantity.

Size can be expressed as an abstract number, without indicating a unit of measurement, which corresponds to numerical value of a physical quantity. A quantitative assessment of a physical quantity, represented by a number indicating the unit of this quantity, is called the value of a physical quantity.

We can talk about the sizes of different units of a given physical quantity. In this case, the size of, for example, a kilogram differs from the size of a pound (1 pound = 32 lots = 96 spools = 409.512 g), pood (1 point = 40 pounds = 1280 lots = 16.3805 kg), etc. d.

Consequently, different interpretations of physical quantities in different countries must be taken into account, otherwise it can lead to insurmountable difficulties, even disasters.

Thus, in 1984, the Canadian passenger plane Boeing-647 made an emergency landing at a vehicle test site after the engines failed during a flight at an altitude of 10 thousand m due to spent fuel. The explanation for this incident was that the instruments on the plane were calibrated in liters, but the instruments of the Canadian airline that refueled the plane were calibrated in gallons (approximately 3.8 L). Thus, almost four times less fuel was filled than required.

So, if there is a certain quantity X, the unit of measurement adopted for it is [X], then the value of a specific physical quantity can be calculated using the formula

X = q [X], (4.1)

Where q – numerical value of a physical quantity; [ X] – unit of physical quantity.

For example, pipe length l= 5m, where l– the value of the length, 5 – its numerical value, m – the unit of length adopted in this case.

Equation (4.1) is called basic measurement equation, showing that the numerical value of a quantity depends on the size of the adopted unit of measurement.

Depending on the comparison area, the values may be homogeneous And heterogeneous. For example, diameter, circumference, wavelength, as a rule, are considered as homogeneous quantities related to a quantity called length.

Within the same system of quantities, homogeneous quantities have the same dimension. However, quantities of the same dimension are not always homogeneous. For example, moment of force and energy are not homogeneous quantities, but have the same dimension.

System of quantities represents a set of quantities together with a set of consistent equations connecting these quantities.

Basic quantity represents a quantity that is conditionally selected for a given system of quantities and is included in the set of basic quantities. For example, the basic quantities of the SI system. The main quantities are not related to each other.

Derived quantity system of quantities is determined through the basic quantities of this system. For example, in a system of quantities where the main quantities are length and mass, mass density is a derived quantity, which is defined as the quotient of mass divided by volume (length to the third power).

Multiple unit is obtained by multiplying a given unit of measurement by an integer greater than one. For example, a kilometer is a decimal multiple of a meter; and an hour is a non-decimal unit that is a multiple of a second.

submultiple unit is obtained by dividing a unit of measurement by an integer greater than one. For example, a millimeter is a decimal unit, a submultiple of a meter.

Non-systemic unit measurement does not belong to this system of units. For example, day, hour, minute are non-systemic units of measurement in relation to the SI system.

Let's introduce another important concept - measurement conversion.

It is understood as the process of establishing a one-to-one correspondence between the sizes of two quantities: the quantity being converted (input) and the quantity transformed as a result of measurement (input).

The set of sizes of the input quantity subjected to transformation using a technical device - a measuring transducer - is called conversion range.

Measurement conversion can be carried out in different ways depending on the types of physical quantities, which are usually divided into three groups.

First group represents quantities on the set of sizes of which only their relationships are determined in the form of comparisons “weaker - stronger”, “softer - harder”, “colder - warmer”, etc.

These relationships are established on the basis of theoretical or experimental studies and are called order relations(equivalence relations).

To the quantities first group include, for example, wind strength (weak, strong, moderate, storm, etc.), hardness, characterized by the ability of the body under study to resist indentation or scratching.

Second group represents quantities for which relations of order (equivalence) are determined not only between the sizes of quantities, but also between the differences of quantities in pairs of their sizes.

These include, for example, time, energy, temperature, determined on the scale of a liquid thermometer.

The possibility of comparing the differences in the sizes of these quantities lies in determining the quantities of the second group.

Thus, when using a mercury thermometer, temperature differences (for example, in the range from +5 to +10 ° C) are considered equal. Thus, in this case, there is both a relation of the order of magnitude (25 “warmer” than 10°C) and an equivalence relation between the differences in pairs of size quantities: the difference of the pair (25–20°C) corresponds to the difference of the pair (10– 5°C).

In both cases, the order relation is unambiguously established using a measuring instrument (measuring transducer), which is the mentioned liquid thermometer.

It is easy to conclude that temperature belongs to the values of both the first and second groups.

Third group quantities are characterized by the fact that on the set of their sizes (except for the indicated relations of order and equivalence characteristic of quantities of the second group), it is possible to perform operations similar to addition or subtraction (additivity property).

The quantities of the third group include a significant number of physical quantities, for example, length, mass.

Thus, two bodies weighing 0.5 kg each, placed on one of the pans of equal-arm scales, are balanced by a weight weighing 1 kg placed on the other pan.

Measurement quality

No science can do without measurements, therefore metrology, as a science of measurements, is in close connection with all other sciences. Therefore, the main concept of metrology is measurement. According to GOST 16263 - 70, measurement is finding the value of a physical quantity (PV) experimentally using special technical means.

The possibility of measurement is determined by a preliminary study of a given property of the measurement object, the construction of abstract models of both the property itself and its carrier - the measurement object as a whole. Therefore, the place of measurement is determined among the methods of cognition that ensure the reliability of the measurement. With the help of metrological procedures, the problems of data generation (recording the results of cognition) are solved. Measurement from this point of view is a method of encoding information and recording the information received.

Measurements provide quantitative information about the object of management or control, without which it is impossible to accurately reproduce all specified conditions of the technical process, ensure high quality of products and effective management of the object. All this constitutes the technical aspect of measurements.

Until 1918, the metric system was introduced in Russia optionally, along with the old Russian and English (inch) systems. Significant changes in metrological activities began to occur after the Council of People's Commissars of the RSFSR signed the decree "On the introduction of the international metric system of weights and measures." The introduction of the metric system in Russia took place from 1918 to 1927. After the Great Patriotic War and to this day, metrological work in our country is carried out under the leadership of the State Committee for Standards (Gosstandart).

In 1960, the XI International Conference on Weights and Measures adopted the International System of VF Units - the SI system. Today, the metric system is legalized in more than 124 countries around the world.

Currently, on the basis of the Main Chamber of Weights and Measures there is the country's highest scientific institution - the All-Russian Research Institute of Metrology named after. DI. Mendeleev (VNIIM). In the institute's laboratories, state standards of units of measurement are developed and stored, physical constants and properties of substances and materials are determined. The institute's work covers linear, angular, optical and photometric, acoustic, electrical and magnetic measurements, measurements of mass, density, force, pressure, viscosity, hardness, speed, acceleration and a number of other quantities.

In 1955, the country's second metrological center was created near Moscow - now the All-Russian Research Institute of Physical, Technical and Radio Engineering Measurements (VNIIFTRI). He develops standards and precision measurement tools in a number of important areas of science and technology: radio electronics, time and frequency services, acoustics, atomic physics, low temperature and high pressure physics.

The third metrological center in Russia is the All-Russian Research Institute of Metrological Service (VNIIMS), the leading organization in the field of applied and legal metrology. He is entrusted with the coordination and scientific and methodological management of the country's metrological service. In addition to those listed, there are a number of regional metrological institutes and centers.

International metrological organizations include the International Organization of Legal Metrology (OIML), formed in 1956. The International Bureau of Legal Metrology operates under the OIML in Paris. Its activities are managed by the International Committee for Legal Metrology. Some metrology issues are addressed by the International Organization for Standardization (ISO).

Physical properties and quantities. Classification of physical quantities.

Measurement scales

All objects of the surrounding world are characterized by their properties.

Property- a philosophical category that expresses such an aspect of an object (phenomenon or process) that determines its difference or commonality with other objects, and is revealed in its relations to them. Property - quality category. For a quantitative description of various properties of physical bodies, phenomena and processes, the concept of quantity is introduced.

Magnitude- this is a measure of an object (phenomenon, process or something else), a measure of what can be distinguished among other properties and assessed in one way or another, including quantitatively. A quantity does not exist on its own; it exists only insofar as there is an object with properties expressed by a given quantity.

Thus, the concept of quantity is a concept of greater generality than quality (property, attribute) and quantity.

Physical properties and quantities

There are two types of quantities: real and ideal.

Ideal quantities (numerical values of quantities, graphs, functions, operators, etc.) mainly relate to mathematics and are a generalization (mathematical model) of specific real concepts. They are calculated in one way or another.

Real values, in turn, are divided as physical And non-physical. Wherein, physical quantity in the general case, can be defined as a quantity characteristic of material objects (bodies, processes, phenomena) studied in the natural (physics, chemistry) and technical sciences. TO non-physical quantities values inherent in social (non-physical) sciences - philosophy, sociology, economics, etc. should be included.

The GOST 16263-70 standard interprets physical quantity, as a numerical expression of a specific property of a physical object, in a qualitative sense common to many physical objects, and in a quantitative sense, absolutely individual for each of them. Individuality in quantitative terms is understood here in the sense that a property can be greater for one object, a certain number of times, or less than for another.

Thus, physical quantities are measured properties of physical objects or processes with the help of which they can be studied.

It is advisable to further classify physical quantities (PV) as measurable And assessed.

Measured physical quantities can be expressed quantitatively in terms of a certain number of established units of measurement. The ability to introduce and use units of measurement is an important distinguishing feature of measured PVs.

Physical quantities for which, for one reason or another, a unit of measurement cannot be introduced, can only be estimated. In this case, evaluation is understood as the operation of assigning a certain number to a given value, carried out according to established rules. Values are assessed using scales.

Non-physical quantities, for which units and scales cannot in principle be introduced, can only be estimated.

Classification of physical quantities

For a more detailed study of PVs, it is necessary to classify them, identifying the general metrological features of their individual groups. Possible classifications of PV are shown in Fig. 2.2.

By types of phenomena they are divided into the following groups:

· real, i.e. describing the physical and physico-chemical properties of substances, materials and products made from them. This group includes mass, density, electrical resistance, capacitance, inductance, etc. Sometimes these PVs are called passive. To measure them, it is necessary to use an auxiliary energy source, with the help of which a measurement information signal is generated. In this case, passive PVs are converted into active ones, which are measured;

· energy, i.e. quantities describing the energy characteristics of the processes of transformation, transmission and use of energy. These include current, voltage, power, energy. These quantities are called active. They can be converted into measurement information signals without the use of auxiliary energy sources;

·
characterizing the course of processes over time. This group includes various types of spectral characteristics, correlation functions, etc.

According to belonging to different groups of physical processes Physics are divided into spatiotemporal, mechanical, thermal, electrical and magnetic, acoustic, light, physicochemical, ionizing radiation, atomic and nuclear physics.

According to the degree of conditional independence from other quantities of this group, PVs are divided into basic (conditionally independent), derivatives (conditionally dependent) and additional. Currently, the SI system uses seven physical quantities, chosen as the main ones: length, time, mass, temperature, electric current, luminous intensity and amount of matter. Additional physical quantities include plane and solid angles.

Based on size availability PVs are divided into dimensional ones, i.e. having dimension and dimensionless.

Physical objects have an unlimited number of properties that manifest themselves in infinite variety. This makes it difficult to reflect them as sets of numbers with limited bit depth, which arises during their measurement. Among the many specific manifestations of properties, there are also several common ones. N.R. Campbell established for the entire variety of properties X of a physical object the presence of three most general manifestations in the relations of equivalence, order and additivity. These relations in mathematical logic are analytically described by the simplest postulates.

When comparing quantities, an order relation is revealed (greater than, less than or equal to), i.e. the relationship between the quantities is determined. Examples of intensive quantities are material hardness, odor, etc.

Intensive quantities can be detected, classified by intensity, subjected to control, quantified by monotonically increasing or decreasing numbers.

Based on the concept of “intensive quantity,” the concepts of physical quantity and its size are introduced. Size of physical quantity- quantitative content in a given object of a property corresponding to the concept of PV.

Measurement scales

In practical activities, it is necessary to carry out measurements of various physical quantities that characterize the properties of bodies, substances, phenomena and processes. Some properties appear only qualitatively, others - quantitatively. Various manifestations (quantitative or qualitative) of one or another property of the object of study form a set, the mappings of whose elements onto an ordered set of numbers, or, in a more general case, conventional signs, form measurement scale this property. The scale of measurement of a quantitative property of a specific physical quantity is the scale of that physical quantity. Thus, physical quantity scale is an ordered sequence of PV values, adopted by agreement based on the results of accurate measurements. The terms and definitions of the theory of measurement scales are set out in document MI 2365-96.

In accordance with the logical structure of the manifestation of properties, five main types of measurement scales are distinguished.

1. Name scale (classification scale). Such scales are used to classify empirical objects whose properties appear only in relation to equivalence. These properties cannot be considered physical quantities, therefore scales of this type are not PV scales. This is the simplest type of scale, based on assigning numbers to the qualitative properties of objects, playing the role of names. In naming scales in which the assignment of a reflected property to a particular equivalence class is carried out using human senses, the most adequate result is the one chosen by the majority of experts. In this case, the correct choice of classes of the equivalent scale is of great importance - they must be reliably distinguished by observers and experts assessing this property. The numbering of objects on a scale of names is carried out according to the principle: “do not assign the same number to different objects.” Numbers assigned to objects can be used to determine the probability or frequency of occurrence of a given object, but they cannot be used for summation or other mathematical operations.

Since these scales are characterized only by equivalence relations, they do not contain the concepts of zero, “more” or “less” and units of measurement. An example of naming scales are widely used color atlases designed for color identification.

2. Order scale (rank scale). If the property of a given empirical object manifests itself in relation to equivalence and order in increasing or decreasing quantitative manifestation of the property, then an order scale can be constructed for it. It is monotonically increasing or decreasing and allows you to establish a greater/lesser ratio between quantities characterizing the specified property. In order scales, zero exists or does not exist, but in principle it is impossible to introduce units of measurement, since a proportionality relation has not been established for them and, accordingly, there is no way to judge how many times more or less specific manifestations of a property are.

In cases where the level of knowledge of a phenomenon does not allow one to accurately establish the relationships that exist between the values of a given characteristic, or the use of a scale is convenient and sufficient for practice, conditional (empirical) order scales are used. Conditional scale is a PV scale, the initial values of which are expressed in conventional units. For example, the Engler viscosity scale, the 12-point Beaufort scale for sea wind strength.

Order scales with reference points marked on them have become widespread. Such scales, for example, include the Mohs scale for determining the hardness of minerals, which contains 10 reference (reference) minerals with different hardness numbers: talc - 1; gypsum - 2; calcium - 3; fluorite - 4; apatite - 5; orthoclase - 6; quartz - 7; topaz - 8; corundum - 9; diamond - 10. The assignment of a mineral to a particular gradation of hardness is carried out on the basis of an experiment, which consists of scratching the test material with a supporting one. If after scratching the tested mineral with quartz (7) a trace remains on it, but after orthoclase (6) there is no trace, then the hardness of the tested material is more than 6, but less than 7. It is impossible to give a more accurate answer in this case.

In conventional scales, the same intervals between the sizes of a given quantity do not correspond to the same dimensions of the numbers displaying the sizes. Using these numbers you can find probabilities, modes, medians, quantiles, but they cannot be used for summation, multiplication and other mathematical operations.

Determining the value of quantities using order scales cannot be considered a measurement, since units of measurement cannot be entered on these scales. The operation of assigning a number to a required value should be considered an estimation. Assessment on order scales is ambiguous and very conditional, as evidenced by the example considered.

3. Interval scale (difference scale). These scales are a further development of order scales and are used for objects whose properties satisfy the relations of equivalence, order and additivity. The interval scale consists of identical intervals, has a unit of measurement and an arbitrarily chosen beginning - the zero point. Such scales include chronology according to various calendars, in which either the creation of the world, or the Nativity of Christ, etc. is taken as the starting point. The Celsius, Fahrenheit and Reaumur temperature scales are also interval scales.

The interval scale defines the actions of adding and subtracting intervals. Indeed, on a time scale, intervals can be summed or subtracted and compared by how many times one interval is greater than another, but adding up the dates of any events is simply pointless.

4. Relationship scale. These scales describe the properties of empirical objects that satisfy the relations of equivalence, order and additivity (scales of the second kind are additive), and in some cases proportionality (scales of the first kind are proportional). Their examples are the scale of mass (second kind), thermodynamic temperature (first kind).

In ratio scales, there is an unambiguous natural criterion for the zero quantitative manifestation of a property and a unit of measurement established by agreement. From a formal point of view, the ratio scale is an interval scale with a natural origin. All arithmetic operations are applicable to the values obtained on this scale, which is important when measuring EF.

Relationship scales are the most advanced. They are described by the equation , where Q is the PV for which the scale is constructed, [Q] is its unit of measurement, q is the numerical value of the PV. The transition from one scale of relations to another occurs in accordance with the equation q 2 = q 1 /.

5. Absolute scales. Some authors use the concept of absolute scales, by which they mean scales that have all the features of ratio scales, but additionally have a natural unambiguous definition of the unit of measurement and do not depend on the adopted system of units of measurement. Such scales correspond to relative values: gain, attenuation, etc. To form many derived units in the SI system, dimensionless and counting units of absolute scales are used.

Note that the scales of names and order are called non-metric (conceptual), and the scales of intervals and ratios are called metric (material). Absolute and metric scales belong to the category of linear. The practical implementation of measurement scales is carried out by standardizing both the scales and measurement units themselves, and, if necessary, the methods and conditions for their unambiguous reproduction.

M. V. Lomonosov

Look around you. What a variety of objects surrounds you: people, animals, trees. This is a TV, a car, an apple, a stone, a light bulb, a pencil, etc. It is impossible to list everything. In physics any object is called a physical body.

How are physical bodies different? To a lot of people. For example, they can have different volumes and shapes. They can consist of different substances. Silver and gold spoons have the same volume and shape. But they consist of different substances: silver and gold. Wooden cube and cylinder have different volume and shape. These are different physical bodies, but made of the same substance - wood.

In addition to physical bodies, there are also physical fields. Fields exist independently of us. They cannot always be detected using human senses. For example, the field around a magnet, field around a charged body. But they are easy to detect using instruments.

Experience shows the position of the electric field lines from two opposite electric charges.

Various changes can occur with physical bodies and fields. A spoon dipped into hot tea heats up. The water in the puddle evaporates and freezes on a cold day. The lamp emits light, girl and dog are running (moving). The magnet becomes demagnetized and its magnetic field weakens. Heating, evaporation, freezing, radiation, movement, demagnetization, etc. - all these changes occurring with physical bodies and fields are called physical phenomena.

By studying physics, you will become familiar with many physical phenomena.

Physical quantities are introduced to describe the properties of physical bodies and physical phenomena. For example, you can describe the properties of a wooden ball and cube using physical quantities such as volume and mass. A physical phenomenon - movement (of a girl, a car, etc.) - can be described by knowing such physical quantities as path, speed, period of time. pay attention to the main feature of a physical quantity: it can be measured using instruments or calculated using the formula. The volume of a body can be measured with a beaker of water, or by measuring the length a, width b and height with a ruler, it can be calculated using the formula

V= a b c.

The volume of a body can be measured with a beaker of water, or you can measure the length a, width b and height with a ruler and calculate it using the formula

All physical quantities have units of measurement. You have heard about some units of measurement many times: kilogram, meter, second, volt, ampere, kilowatt, etc. You will become more familiar with physical quantities in the process of studying physics.

Think and answer

What is called the physical body? A physical phenomenon?
What is the main sign of a physical quantity? Name the physical quantities known to you.
From the above concepts, name those that relate to: a) physical bodies; b) physical phenomena; c) physical quantities: 1) drop; 2) heating; 3) length; 4) thunderstorm; 5) cube; 6) volume; 7) wind; 8) drowsiness; 9) temperature; 10) pencil; 11) period of time; 12) sunrise; 13) speed; 14) beauty.

Homework

We have a “measuring device” in our bodies. This is a heart with which you can measure (with not very high accuracy) a period of time. Determine by your pulse (the number of heartbeats) the time period for filling a glass with tap water. Consider the time of one blow to be approximately one second. Compare this time with the clock readings. How different are the results obtained?

A physical quantity is one of the properties of a physical object (phenomenon, process), which is qualitatively common to many physical objects, while differing in quantitative value.

The purpose of measurements is to determine the value of a physical quantity - a certain number of units accepted for it (for example, the result of measuring the mass of a product is 2 kg, the height of a building is 12 m, etc.).

Depending on the degree of approximation to objectivity, true, actual and measured values of a physical quantity are distinguished.

This is a value that ideally reflects the corresponding property of an object in qualitative and quantitative terms. Due to the imperfection of measurement tools and methods, it is practically impossible to obtain the true values of quantities. They can only be imagined theoretically. And the values obtained during measurement only approach the true value to a greater or lesser extent.

This is a value of a quantity found experimentally that is so close to the true value that it can be used instead for a given purpose.

This is the value obtained by measurement using specific methods and measuring instruments.

9. Classification of measurements according to the dependence of the measured value on time and according to sets of measured values.

According to the nature of the change in the measured value - static and dynamic measurements.

Dynamic measurement - a measurement of a quantity whose size changes over time. A rapid change in the size of the measured quantity requires its measurement with the most accurate determination of the moment in time. For example, measuring the distance to the Earth's surface from a balloon or measuring the constant voltage of an electric current. Essentially, a dynamic measurement is a measurement of the functional dependence of the measured quantity on time.

Static measurement - measurement of a quantity that is taken into account in accordance with the assigned measurement task and does not change throughout the measurement period. For example, measuring the linear size of a manufactured product at normal temperature can be considered static, since temperature fluctuations in the workshop at the level of tenths of a degree introduce a measurement error of no more than 10 μm/m, which is insignificant compared to the manufacturing error of the part. Therefore, in this measurement task, the measured quantity can be considered unchanged. When calibrating a line length measure against the state primary standard, thermostatting ensures the stability of maintaining the temperature at the level of 0.005 °C. Such temperature fluctuations cause a thousand times smaller measurement error - no more than 0.01 μm/m. But in this measurement task it is essential, and taking into account temperature changes during the measurement process becomes a condition for ensuring the required measurement accuracy. Therefore, these measurements should be carried out using the dynamic measurement technique.

According to the existing sets of measured values on electrical ( current, voltage, power) , mechanical ( mass, number of products, effort); , thermal power(temperature, pressure); , physical(density, viscosity, turbidity); chemical(composition, chemical properties, concentration) , radio engineering etc.

Classification of measurements according to the method of obtaining the result (by type).

According to the method of obtaining measurement results, they are distinguished: direct, indirect, cumulative and joint measurements.

Direct measurements are those in which the desired value of the measured quantity is found directly from experimental data.

Indirect measurements are those in which the desired value of the measured quantity is found on the basis of a known relationship between the measured quantity and quantities determined using direct measurements.

Cumulative measurements are those in which several quantities of the same name are simultaneously measured and the determined value is found by solving a system of equations that is obtained on the basis of direct measurements of quantities of the same name.

Joint measurements are the measurements of two or more quantities of different names to find the relationship between them.

Classification of measurements according to the conditions that determine the accuracy of the result and the number of measurements to obtain the result.

According to the conditions that determine the accuracy of the result, measurements are divided into three classes:

1. Measurements of the highest possible accuracy achievable with the existing level of technology.

These include, first of all, standard measurements related to the highest possible accuracy of reproducing established units of physical quantities, and, in addition, measurements of physical constants, primarily universal ones (for example, the absolute value of the acceleration of gravity, the gyromagnetic ratio of a proton, etc.).

This class also includes some special measurements that require high accuracy.

2. Control and verification measurements, the error of which, with a certain probability, should not exceed a certain specified value.

These include measurements performed by laboratories for state supervision of the implementation and compliance with standards and the state of measuring equipment and factory measurement laboratories, which guarantee the error of the result with a certain probability not exceeding a certain predetermined value.

3. Technical measurements in which the error of the result is determined by the characteristics of the measuring instruments.

Examples of technical measurements are measurements performed during the production process at machine-building enterprises, on switchboards of power plants, etc.

Based on the number of measurements, measurements are divided into single and multiple.

A single measurement is a measurement of one quantity made once. In practice, single measurements have a large error; therefore, to reduce the error, it is recommended to perform measurements of this type at least three times, and take their arithmetic average as the result.

Multiple measurements are measurements of one or more quantities performed four or more times. A multiple measurement is a series of single measurements. The minimum number of measurements at which a measurement can be considered multiple is four. The result of multiple measurements is the arithmetic average of the results of all measurements taken. With repeated measurements, the error is reduced.

Classification of random measurement errors.

Random error is a component of measurement error that changes randomly during repeated measurements of the same quantity.

1) Rough - does not exceed the permissible error

2) A miss is a gross error, depends on the person

3) Expected - obtained as a result of the experiment during creation. conditions

Concept of metrology

Metrology– the science of measurements, methods and means of ensuring their unity and methods of achieving the required accuracy. It is based on a set of terms and concepts, the most important of which are given below.

Physical quantity- a property that is qualitatively common to many physical objects, but quantitatively individual for each object. Physical quantities are length, mass, density, force, pressure, etc.

Unit of physical quantity is considered to be the quantity that, by definition, is assigned a value equal to 1. For example, mass 1 kg, force 1 N, pressure 1 Pa. In different systems of units, units of the same quantity may differ in size. For example, for a force of 1 kgf ≈ 10 N.

Physical quantity value– numerical assessment of the physical size of a specific object in accepted units. For example, the mass of a brick is 3.5 kg.

Technical Dimension– determination of the values of various physical quantities using special technical methods and means. During laboratory tests, the values of geometric dimensions, mass, temperature, pressure, force, etc. are determined. All technical measurements must meet the requirements of unity and accuracy.

Direct measurement– experimental comparison of a given value with another, taken as unit, by means of reading on the instrument scale. For example, measuring length, mass, temperature.

Indirect measurements– results obtained using the results of direct measurements by calculations using known formulas. For example, determining the density and strength of a material.

Unity of measurements– a state of measurements in which their results are expressed in legal units and measurement errors are known with a given probability. Unity of measurements is necessary in order to be able to compare the results of measurements taken in different places, at different times, using a variety of instruments.

Accuracy of measurements– quality of measurements, reflecting the closeness of the results obtained to the true value of the measured value. Distinguish between true and actual values of physical quantities.

True meaning physical quantity ideally reflects the corresponding properties of the object in qualitative and quantitative terms. The true value is free from measurement errors. Since all values of a physical quantity are found empirically and they contain measurement errors, the true value remains unknown.

Real value physical quantities are found experimentally. It is so close to the true value that for certain purposes it can be used instead. In technical measurements, the value of a physical quantity found with an error acceptable by technical requirements is taken as the actual value.

Measurement error– deviation of the measurement result from the true value of the measured value. Since the true value of the measured quantity remains unknown, in practice the measurement error is only approximately estimated by comparing the measurement results with the value of the same quantity obtained with an accuracy several times higher. Thus, the error in measuring the dimensions of a sample with a ruler, which is ± 1 mm, can be estimated by measuring the sample with a caliper with an error of no more than ± 0.5 mm.

Absolute error expressed in units of the measured quantity.

Relative error- the ratio of the absolute error to the actual value of the measured value.

Measuring instruments are technical means used in measurements and having standardized metrological properties. Measuring instruments are divided into measures and measuring instruments.

Measure– a measuring instrument designed to reproduce a physical quantity of a given size. For example, a weight is a measure of mass.

Measuring device– a measuring instrument that serves to reproduce measurement information in a form accessible to perception by an observer. The simplest measuring instruments are called measuring instruments. For example, a ruler, a caliper.

The main metrological indicators of measuring instruments are:

The scale division value is the difference in the values of the measured quantity, corresponding to two adjacent scale marks;

The initial and final values of the scale are, respectively, the smallest and largest values of the measured value indicated on the scale;

Measurement range is the range of values of the measured value for which permissible errors are normalized.

Measurement error– the result of mutual superposition of errors caused by various reasons: errors of the measuring instruments themselves, errors arising when using the device and reading measurement results and errors from non-compliance with measurement conditions. With a sufficiently large number of measurements, the arithmetic mean of the measurement results approaches the true value, and the error decreases.

Systematic error- an error that remains constant or changes naturally with repeated measurements and arises for well-known reasons. For example, the shift of the instrument scale.

Random error is an error in which there is no natural connection with previous or subsequent errors. Its appearance is caused by many random reasons, the influence of which on each measurement cannot be taken into account in advance. The reasons leading to the appearance of a random error include, for example, heterogeneity of the material, irregularities during sampling, and errors in instrument readings.

If the so-called gross error, which significantly increases the error expected under given conditions, then such measurement results are excluded from consideration as unreliable.

The unity of all measurements is ensured by the establishment of units of measurement and the development of their standards. Since 1960, the International System of Units (SI) has been in force, which replaced the complex set of systems of units and individual non-system units developed on the basis of the metric system of measures. In Russia, the SI system has been adopted as standard, and its use in the field of construction has been regulated since 1980.

Lecture 2. PHYSICAL QUANTITIES. UNITS OF MEASUREMENT

2.1 Physical quantities and scales

2.2 Units of physical quantities

2.3. International System of Units (SI System)

2.4 Physical quantities of technological processes

food production

2.1 Physical quantities and scales

A physical quantity is a property that is qualitatively common to many physical objects (physical systems, their states and processes occurring in them), but quantitatively individual for each of them.

Individual in quantitative terms should be understood in such a way that the same property for one object can be a certain number of times greater or less than for another.

Typically, the term "physical quantity" is used to refer to properties or characteristics that can be quantified. Physical quantities include mass, length, time, pressure, temperature, etc. All of them determine physical properties that are general in qualitative terms; their quantitative characteristics may be different.

It is advisable to distinguish physical quantities into measured and assessed. Measured EF can be expressed quantitatively in the form of a certain number of established units of measurement. The possibility of introducing and using the latter is an important distinguishing feature of measured EF.

However, there are properties such as taste, smell, etc., for which units cannot be entered. Such quantities can be estimated. Values are assessed using scales.

By accuracy of the result There are three types of values of physical quantities: true, actual, measured.

True value of a physical quantity(true value of a quantity) - the value of a physical quantity that, in qualitative and quantitative terms, would ideally reflect the corresponding property of the object.

The postulates of metrology include

The true value of a certain quantity exists and it is constant

The true value of the measured quantity cannot be found.

The true value of a physical quantity can only be obtained as a result of an endless process of measurements with endless improvement of methods and measuring instruments. For each level of development of measuring technology, we can only know the actual value of a physical quantity, which is used instead of the true one.

Real value of a physical quantity– the value of a physical quantity found experimentally and so close to the true value that it can replace it for the given measurement task. A typical example illustrating the development of measurement technology is the measurement of time. At one time, the unit of time - the second - was defined as 1/86400 of the average solar day with an error of 10 -7 . Currently, the second is determined with an error of 10 -14 , i.e., we are 7 orders of magnitude closer to the true value of determining time at the reference level.

The actual value of a physical quantity is usually taken to be the arithmetic mean of a series of quantity values obtained with equal-precision measurements, or the weighted arithmetic mean with unequal-precision measurements.

Measured value of a physical quantity– the value of a physical quantity obtained using a specific technique.

By type of PV phenomena divided into the following groups :

- real , those. describing the physical and physicochemical properties of substances. Materials and products made from them. These include mass, density, etc. These are passive PVs, because to measure them, it is necessary to use auxiliary energy sources, with the help of which a signal of measurement information is generated.

- energy – describing the energy characteristics of the processes of transformation, transmission and use of energy (energy, voltage, power. These quantities are active. They can be converted into measurement information signals without the use of auxiliary energy sources;

- characterizing the flow of time processes . This group includes various kinds of spectral characteristics, correlation functions, etc.

According to the degree of conditional dependence on other values of PV divided into basic and derivative

Basic physical quantity– a physical quantity included in a system of quantities and conventionally accepted as independent of other quantities of this system.

The choice of physical quantities accepted as basic and their number is carried out arbitrarily. First of all, the quantities that characterize the basic properties of the material world were chosen as the main ones: length, mass, time. The remaining four basic physical quantities are chosen in such a way that each of them represents one of the branches of physics: current strength, thermodynamic temperature, amount of matter, light intensity.

Each basic physical quantity of a system of quantities is assigned a symbol in the form of a lowercase letter of the Latin or Greek alphabet: length - L, mass - M, time - T, electric current - I, temperature - O, amount of substance - N, light intensity - J. These symbols are included in the name of the system of physical quantities. Thus, the system of physical quantities of mechanics, the main quantities of which are length, mass and time, is called the “LMT system”.

Derived physical quantity– a physical quantity included in a system of quantities and determined through the basic quantities of this system.

1.3 Physical quantities and their measurements

Physical quantity – one of the properties of a physical object (physical system, phenomenon or process), common in qualitative terms for many physical objects, but quantitatively individual for each of them. We can also say that a physical quantity is a quantity that can be used in the equations of physics, and by physics here we mean science and technology in general.

Word " magnitude" is often used in two senses: as a general property to which the concept of more or less is applicable, and as the quantity of this property. In the latter case, we would have to talk about the “magnitude of a quantity,” so in what follows we will talk about quantity precisely as a property of a physical object, and in the second sense, as the meaning of a physical quantity.

Recently, the division of quantities into physical and non-physical , although it should be noted that there is no strict criterion for such a division of values. At the same time, under physical understand quantities that characterize the properties of the physical world and are used in physical sciences and technology. There are units of measurement for them. Physical quantities, depending on the rules of their measurement, are divided into three groups:

Quantities characterizing the properties of objects (length, mass);

quantities characterizing the state of the system (pressure,

temperature);

Quantities characterizing processes (speed, power).

TO non-physical refer to quantities for which there are no units of measurement. They can characterize both the properties of the material world and concepts used in social sciences, economics, and medicine. In accordance with this division of quantities, it is customary to distinguish between measurements of physical quantities and non-physical measurements . Another expression of this approach is two different understandings of the concept of measurement:

measurement in in the narrow sense as an experimental comparison

one measurable quantity with another known quantity

the same quality adopted as a unit;

measurement in in a broad sense how to find matches

between numbers and objects, their states or processes according to

known rules.

The second definition appeared in connection with the recent widespread use of measurements of non-physical quantities that appear in biomedical research, in particular in psychology, economics, sociology and other social sciences. In this case, it would be more correct to talk not about measurement, but about estimating quantities , understanding assessment as establishing the quality, degree, level of something in accordance with established rules. In other words, this is an operation of attributing, by calculating, finding or determining a number, a quantity characterizing the quality of an object, according to established rules. For example, determining the strength of wind or earthquake, grading figure skaters or assessing students' knowledge on a five-point scale.

Concept assessment quantities should not be confused with the concept of estimating quantities, associated with the fact that as a result of measurements we actually do not receive the true value of the measured quantity, but only its assessment, to one degree or another close to this value.

The concept discussed above measurement", which presupposes the presence of a unit of measurement (measure), corresponds to the concept of measurement in the narrow sense and is more traditional and classical. In this sense, it will be understood below - as a measurement of physical quantities.

Below are about basic concepts , related to a physical quantity (hereinafter, all basic concepts in metrology and their definitions are given according to the above-mentioned recommendation on interstate standardization RMG 29-99):

- size of a physical quantity - quantitative certainty of a physical quantity inherent in a specific material object, system, phenomenon or process;

- physical quantity value - expression of the size of a physical quantity in the form of a certain number of units accepted for it;

- true value of a physical quantity - the value of a physical quantity that ideally characterizes the corresponding physical quantity in qualitative and quantitative terms (can be correlated with the concept of absolute truth and is obtained only as a result of an endless process of measurements with endless improvement of methods and measuring instruments);

actual value of a physical quantity  the value of a physical quantity obtained experimentally and so close to the true value that it can be used instead of it in the given measurement task;

unit of measurement of physical quantity  a physical quantity of a fixed size, which is conventionally assigned a numerical value equal to 1, and used for the quantitative expression of physical quantities similar to it;

system of physical quantities  a set of physical quantities formed in accordance with accepted principles, when some quantities are taken as independent, while others are defined as functions of these independent quantities;

main physical quantity – a physical quantity included in a system of quantities and conventionally accepted as independent of other quantities of this system.

derived physical quantity – a physical quantity included in a system of quantities and determined through the basic quantities of this system;

system of units of physical units  a set of basic and derived units of physical quantities, formed in accordance with the principles for a given system of physical quantities.

If I wanted to read, I haven't yet
knowing the letters, this would be nonsense.
In the same way, if I wanted to judge
about natural phenomena, without having any
ideas about the beginnings of things, this
it would be just as nonsensical.
M. V. Lomonosov

Rice. 6

How are physical bodies different? To a lot of people. For example, they can have different volumes and shapes. They can consist of different substances. Silver and gold spoons (Fig. 6) have the same volume and shape. But they consist of different substances: silver and gold. The wooden cube and ball (Fig. 7) have different volumes and shapes. These are different physical bodies, but made of the same substance - wood.

Rice. 7

In addition to physical bodies, there are also physical fields. Fields exist independently of us. They cannot always be detected using human senses. For example, the field around a magnet (Fig. 8), the field around a charged body (Fig. 9). But they are easy to detect using instruments.

Rice. 8

Rice. 9

Various changes can occur with physical bodies and fields. A spoon dipped into hot tea heats up. The water in the puddle evaporates and freezes on a cold day. The lamp (Fig. 10) emits light, the girl and the dog are running (moving) (Fig. 11). The magnet becomes demagnetized and its magnetic field weakens. Heating, evaporation, freezing, radiation, movement, demagnetization, etc. - all these changes occurring with physical bodies and fields are called physical phenomena.

Rice. 10

By studying physics, you will become familiar with many physical phenomena.

Rice. eleven

Physical quantities are introduced to describe the properties of physical bodies and physical phenomena. For example, you can describe the properties of a wooden ball and cube using physical quantities such as volume and mass. A physical phenomenon - movement (of a girl, a car, etc.) - can be described by knowing such physical quantities as path, speed, period of time. Pay attention to the main sign of a physical quantity: it can be measured using instruments or calculated using the formula. The volume of a body can be measured with a beaker of water (Fig. 12, a), or by measuring the length a, width b and height c with a ruler (Fig. 12, b), it can be calculated using the formula

V = a. b. c.

Rice. 12

Think and answer

What is called the physical body? A physical phenomenon?
What is the main sign of a physical quantity? Name the physical quantities known to you.
From the above concepts, name those that relate to: a) physical bodies; b) physical phenomena; c) physical quantities: 1) drop; 2) heating; 3) length; 4) thunderstorm; 5) cube; 6) volume; 7) wind; 8) drowsiness; 9) temperature; 10) pencil; 11) period of time; 12) sunrise; 13) speed; 14) beauty.

Homework