What is kg m. Basic physical quantities and their units of measurement
What does it mean to measure a physical quantity? What is a unit of physical quantity called? Here you will find answers to these very important questions.
1. Let's find out what is called a physical quantity
For a long time, people have used their characteristics to more accurately describe certain events, phenomena, properties of bodies and substances. For example, when comparing the bodies that surround us, we say that the book is smaller than bookshelf, and the horse is larger than the cat. This means that the volume of the horse is greater than the volume of the cat, and the volume of the book is less than the volume of the cabinet.
Volume is an example of a physical quantity that characterizes general property bodies occupy one or another part of space (Fig. 1.15, a). Wherein numeric value the volume of each body individually.
Rice. 1.15 To characterize the property of bodies to occupy one or another part of space, we use the physical quantity volume (o, b), to characterize movement - speed (b, c)
A general characteristic of many material objects or phenomena, which can acquire individual meaning for each of them, is called physical quantity.
Another example of a physical quantity is the familiar concept of “speed”. All moving bodies change their position in space over time, but the speed of this change is different for each body (Fig. 1.15, b, c). Thus, in one flight, an airplane manages to change its position in space by 250 m, a car by 25 m, a person by I m, and a turtle by only a few centimeters. That's why physicists say that speed is a physical quantity that characterizes the speed of movement.
It is not difficult to guess that volume and speed are not all the physical quantities that physics operates with. Mass, density, force, temperature, pressure, voltage, illumination - this is only a small part of the physical quantities that you will become familiar with while studying physics.
2. Find out what it means to measure a physical quantity
In order to quantitatively describe the properties of any material object or physical phenomenon, it is necessary to establish the value of the physical quantity that characterizes this object or phenomenon.
The value of physical quantities is obtained by measurements (Fig. 1.16-1.19) or calculations.
Rice. 1.16. “There are 5 minutes left before the train departs,” you measure the time with excitement.
Rice. 1.17 “I bought a kilogram of apples,” says mom about her mass measurements
Rice. 1.18. “Dress warmly, it’s cooler outside today,” your grandmother says after measuring the air temperature outside.
Rice. 1.19. “My blood pressure has risen again,” a woman complains after measuring her blood pressure.
To measure a physical quantity means to compare it with a homogeneous quantity taken as a unit. 
Rice. 1.20 If a grandmother and grandson measure distance in steps, they will always get different results
Let's give an example from fiction: “After walking three hundred steps along the river bank, the small detachment entered the arches of a dense forest, along the winding paths of which they had to wander for ten days.” (J. Verne “The Fifteen-Year-Old Captain”)
Rice. 1.21.
The heroes of the novel by J. Verne measured the distance traveled, comparing it with the step, that is, the unit of measurement was the step. There were three hundred such steps. As a result of the measurement, a numerical value (three hundred) of a physical quantity (path) in selected units (steps) was obtained.
Obviously, the choice of such a unit does not allow comparing the measurement results obtained different people, since everyone’s step length is different (Fig. 1.20). Therefore, for the sake of convenience and accuracy, people long ago began to agree to measure the same physical quantity with the same units. Nowadays, in most countries of the world, the International System of Units of Measurement, adopted in 1960, is in force, which is called the “System International” (SI) (Fig. 1.21).
In this system, the unit of length is the meter (m), time - the second (s); Volume is measured in cubic meters (m3), and speed is measured in meters per second (m/s). You will learn about other SI units later.
3. Remember multiples and submultiples
From a mathematics course you know that to abbreviate the notation of large and small values different sizes use multiples and submultiples.
Multiples are units that are 10, 100, 1000 or more times larger than the base units. Sub-multiple units are units that are 10, 100, 1000 or more times smaller than the main ones.
Prefixes are used to write multiples and submultiples. For example, units of length that are multiples of one meter are a kilometer (1000 m), a decameter (10 m).
Units of length subordinate to one meter are decimeter (0.1 m), centimeter (0.01 m), micrometer (0.000001 m), and so on.
The table shows the most commonly used prefixes.
4. Getting to know the measuring instruments
Scientists measure physical quantities using measuring instruments. The simplest of them - a ruler, a tape measure - are used to measure distance and linear dimensions of the body. You are also well aware of such measuring instruments as a watch - a device for measuring time, a protractor - a device for measuring angles on a plane, a thermometer - a device for measuring temperature, and some others (Fig. 1.22, p. 20). You still have to get acquainted with many measuring instruments.
Most measuring instruments have a scale that allows for measurement. In addition to the scale, the device indicates the units in which the value measured by this device is expressed*.
On the scale you can set the two most important characteristics device: measurement limits and division value.
Measurement limits- these are the largest and smallest values of a physical quantity that can be measured by this device.
Nowadays, electronic measuring instruments are widely used, in which the value of the measured quantities is displayed on the screen in the form of numbers. Measurement limits and units are determined from the device passport or are set with a special switch on the device panel.
Rice. 1.22. Measuring instruments
Value of division- this is the value of the smallest scale division of the measuring device.
For example, the upper measurement limit of a medical thermometer (Fig. 1.23) is 42 °C, the lower one is 34 °C, and the scale division of this thermometer is 0.1 °C.
We remind you: to determine the price of a scale division of any device, it is necessary to divide the difference of any two values indicated on the scale by the number of divisions between them.
Rice. 1.23. Medical thermometer
- Let's sum it up
A general characteristic of material objects or phenomena, which can acquire individual meaning for each of them, is called a physical quantity.
To measure a physical quantity means to compare it with a homogeneous quantity taken as a unit.
As a result of measurements, we obtain the value of physical quantities.
When talking about the value of a physical quantity, you should indicate its numerical value and unit.
Measuring instruments are used to measure physical quantities.
To reduce the recording of numerical values of large and small physical quantities, multiple and submultiple units are used. They are formed using prefixes.
- Control questions
1. Define a physical quantity. How do you understand it?
2. What does it mean to measure a physical quantity?
3. What is meant by the value of a physical quantity?
4. Name all the physical quantities mentioned in the excerpt from J. Verne’s novel given in the text of the paragraph. What is their numerical value? units?
5. What prefixes are used to form submultiple units? multiple units?
6. What characteristics of the device can be set using the scale?
7. What is the division price called?
- Exercises
1. Name the ones you know physical quantities. Specify the units of these quantities. What instruments are used to measure them?
2. In Fig. Figure 1.22 shows some measuring instruments. Is it possible, using only a drawing, to determine the price of division of the scales of these instruments? Justify your answer.
3. Express in meters following values physical size: 145 mm; 1.5 km; 2 km 32 m.
4. Write down the following values of physical quantities using multiples or submultiples: 0.0000075 m - diameter of red blood cells; 5,900,000,000,000 m - the radius of the orbit of the planet Pluto; 6,400,000 m is the radius of planet Earth.
5 Determine the measurement limits and the price of division of the scales of the instruments that you have at home.
6. Remember the definition of a physical quantity and prove that length is a physical quantity.
- Physics and technology in Ukraine
One of the outstanding physicists of our time - Lev Davidovich Landau (1908-1968) - demonstrated his abilities while still studying at high school. After graduating from university, he interned with one of the creators quantum physics Niels Bohr. Already at the age of 25, he headed the theoretical department of the Ukrainian Institute of Physics and Technology and the department of theoretical physics at Kharkov University. Like most outstanding theoretical physicists, Landau had an extraordinary breadth of scientific interests. Nuclear physics, plasma physics, the theory of superfluidity of liquid helium, the theory of superconductivity - Landau made significant contributions to all these areas of physics. For work in physics low temperatures he was awarded the Nobel Prize.
Physics. 7th grade: Textbook / F. Ya. Bozhinova, N. M. Kiryukhin, E. A. Kiryukhina. - X.: Publishing house "Ranok", 2007. - 192 p.: ill.
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Books
- Hydraulics. Textbook and workshop for academic bachelor's degree, V.A. Kudinov. The textbook outlines the basic physical and mechanical properties of liquids, issues of hydrostatics and hydrodynamics, provides the basics of the theory of hydrodynamic similarity and mathematical modeling...
- Hydraulics 4th ed., trans. and additional Textbook and workshop for academic bachelor's degree, Eduard Mikhailovich Kartashov. The textbook outlines the basic physical and mechanical properties of liquids, issues of hydrostatics and hydrodynamics, provides the basics of the theory of hydrodynamic similarity and mathematical modeling...
Physics, as a science that studies natural phenomena, uses standard research methods. The main stages can be called: observation, putting forward a hypothesis, conducting an experiment, substantiating the theory. During the observation, it is established distinctive features phenomena, the course of its course, possible reasons and consequences. A hypothesis allows us to explain the course of a phenomenon and establish its patterns. The experiment confirms (or does not confirm) the validity of the hypothesis. Allows you to establish a quantitative relationship between quantities during an experiment, which leads to an accurate establishment of dependencies. A hypothesis confirmed by experiment forms the basis of a scientific theory.
No theory can claim reliability if it has not received complete and unconditional confirmation during the experiment. Carrying out the latter is associated with measurements of physical quantities characterizing the process. - this is the basis of measurements.
What it is
Measurement concerns those quantities that confirm the validity of the hypothesis about patterns. A physical quantity is a scientific characteristic of a physical body, the qualitative relation of which is common to many similar bodies. For each body, this quantitative characteristic is purely individual.
If we turn to the specialized literature, then in the reference book by M. Yudin et al. (1989 edition) we read that a physical quantity is: “a characteristic of one of the properties of a physical object (physical system, phenomenon or process), common in qualitatively for many physical objects, but quantitatively individual for each object.”
Ozhegov's dictionary (1990 edition) states that a physical quantity is “the size, volume, extension of an object.”
For example, length is a physical quantity. Mechanics interprets length as the distance traveled, electrodynamics uses the length of the wire, and in thermodynamics a similar value determines the thickness of the walls of blood vessels. The essence of the concept does not change: the units of quantities can be the same, but the meaning can be different.
A distinctive feature of a physical quantity, say, from a mathematical one, is the presence of a unit of measurement. Meter, foot, arshin are examples of units of length.
Units
To measure a physical quantity, it must be compared with the quantity taken as a unit. Remember the wonderful cartoon “Forty-Eight Parrots”. To determine the length of the boa constrictor, the heroes measured its length in parrots, baby elephants, and monkeys. In this case, the length of the boa constrictor was compared with the height of other cartoon characters. The result depended quantitatively on the standard.
Quantities are a measure of its measurement in a certain system of units. Confusion in these measures arises not only due to imperfection and heterogeneity of measures, but sometimes also due to the relativity of units.
Russian measure of length - arshin - the distance between the index and thumb hands. However, everyone's hands are different, and the arshin measured by the hand of an adult man is different from the arshin measured by the hand of a child or woman. The same discrepancy in length measures concerns fathoms (the distance between the fingertips of hands spread out to the sides) and elbows (the distance from the middle finger to the elbow of the hand).
It is interesting that small men were hired as clerks in the shops. Cunning merchants saved fabric using slightly smaller measures: arshin, cubit, fathom.
Systems of measures
Such a variety of measures existed not only in Russia, but also in other countries. The introduction of units of measurement was often arbitrary; sometimes these units were introduced only because of the convenience of their measurement. For example, to measure atmospheric pressure, mmHg was entered. Known in which a tube filled with mercury was used, it was possible to introduce such an unusual value.
The engine power was compared with (which is still practiced in our time).
Various physical quantities made the measurement of physical quantities not only complex and unreliable, but also complicating the development of science.
Unified system of measures
A unified system of physical quantities, convenient and optimized in every industrialized country, has become urgent need. The idea of choosing as few units as possible was adopted as a basis, with the help of which other quantities could be expressed in mathematical relationships. Such basic quantities should not be related to each other; their meaning is determined unambiguously and clearly in any economic system.
They tried to solve this problem in various countries. The creation of a unified GHS, ISS and others) was undertaken repeatedly, but these systems were inconvenient either from a scientific point of view or in domestic and industrial use.
The task, posed at the end of the 19th century, was solved only in 1958. A unified system was presented at a meeting of the International Committee for Legal Metrology.
Unified system of measures
The year 1960 was marked by the historic meeting of the General Conference on Weights and Measures. A unique system called “Systeme internationale d"unites” (abbreviated SI) was adopted by the decision of this honorable meeting. In the Russian version, this system is called the International System (abbreviation SI).
The basis is 7 main units and 2 additional ones. Their numerical value is determined in the form of a standard
Table of physical quantities SI
Name of main unit | Measured quantity | Designation |
|
International | Russian |
||
Basic units |
|||
kilogram | |||
Current strength | |||
Temperature | |||
Quantity of substance | |||
The power of light | |||
Additional units |
|||
Flat angle | |||
Steradian | Solid angle | ||
The system itself cannot consist of only seven units, since the variety of physical processes in nature requires the introduction of more and more new quantities. The structure itself provides not only for the introduction of new units, but also for their interrelation in the form of mathematical relationships (they are more often called dimensional formulas).
A unit of physical quantity is obtained using multiplication and division of the basic units in the dimensional formula. The absence of numerical coefficients in such equations makes the system not only convenient in all respects, but also coherent (consistent).
Derived units
The units of measurement that are formed from the seven basic ones are called derivatives. In addition to the basic and derived units, there was a need to introduce additional ones (radians and steradians). Their dimension is considered to be zero. The lack of measuring instruments to determine them makes it impossible to measure them. Their introduction is due to their use in theoretical research. For example, the physical quantity “force” in this system is measured in newtons. Since force is a measure of the mutual action of bodies on each other, which is the reason for the variation in the speed of a body of a certain mass, it can be defined as the product of a unit of mass by a unit of speed divided by a unit of time:
F = k٠M٠v/T, where k is the proportionality coefficient, M is the unit of mass, v is the unit of speed, T is the unit of time.
SI gives the following formula for dimensions: H = kg٠m/s 2, where three units are used. And the kilogram, and the meter, and the second are classified as basic. The proportionality factor is 1.
It is possible to introduce dimensionless quantities, which are defined as a ratio of homogeneous quantities. These include, as is known, equal to the ratio of the friction force to the normal pressure force.
Table of physical quantities derived from basic ones
Unit name | Measured quantity | Dimensional formula |
kg٠m 2 ٠s -2 |
||
pressure | kg٠ m -1 ٠s -2 |
|
magnetic induction | kg ٠А -1 ٠с -2 |
|
electrical voltage | kg ٠m 2 ٠s -3 ٠A -1 |
|
Electrical resistance | kg ٠m 2 ٠s -3 ٠A -2 |
|
Electric charge | ||
power | kg ٠m 2 ٠s -3 |
|
Electrical capacity | m -2 ٠kg -1 ٠c 4 ٠A 2 |
|
Joule to Kelvin | Heat capacity | kg ٠m 2 ٠s -2 ٠K -1 |
Becquerel | Activity of a radioactive substance | |
Magnetic flux | m 2 ٠kg ٠s -2 ٠A -1 |
|
Inductance | m 2 ٠kg ٠s -2 ٠A -2 |
|
Absorbed dose | ||
Equivalent radiation dose | ||
Illumination | m -2 ٠kd ٠av -2 |
|
Light flow | ||
Strength, weight | m ٠kg ٠s -2 |
|
Electrical conductivity | m -2 ٠kg -1 ٠s 3 ٠A 2 |
|
Electrical capacity | m -2 ٠kg -1 ٠c 4 ٠A 2 |
Non-system units
The use of historically established quantities that are not included in the SI or differ only by a numerical coefficient is allowed when measuring quantities. These are non-systemic units. For example, mm of mercury, x-ray and others.
Numerical coefficients are used to introduce submultiples and multiples. Prefixes match a certain number. Examples include centi-, kilo-, deca-, mega- and many others.
1 kilometer = 1000 meters,
1 centimeter = 0.01 meters.
Typology of quantities
We will try to indicate several basic features that allow us to establish the type of value.
1. Direction. If the action of a physical quantity is directly related to the direction, it is called vector, others - scalar.
2. Availability of dimension. The existence of a formula for physical quantities makes it possible to call them dimensional. If all units in a formula have a zero degree, then they are called dimensionless. It would be more correct to call them quantities with a dimension equal to 1. After all, the concept of a dimensionless quantity is illogical. The main property - dimension - has not been canceled!
3. If possible, addition. An additive quantity, the value of which can be added, subtracted, multiplied by a coefficient, etc. (for example, mass) is a physical quantity that is summable.
4. In relation to the physical system. Extensive - if its value can be compiled from the values of the subsystem. An example would be area measured in square meters. Intensive - a quantity whose value does not depend on the system. These include temperature.
Living in time, we don’t know time
Thus we do not understand ourselves
At such a time, however, were we born?
What time will tell us: “Go away”!
And how do we recognize what our time means?
And what kind of future does our time hide?
But time is us! No one else!
We are with you!P. Fleming
Among the numerous physical quantities, there are basic ones through which all others are expressed using certain quantitative relationships. This - length, time and mass. Let's take a closer look at these quantities and their units of measurement.
1. LENGTH. METHODS OF MEASUREMENT OF DISTANCES
Length
–
measure for measuring distance
. It characterizes extension in space. Attempts at subjective measurements of length were noted more than 4,000 years ago: in the 3rd century in China, a device for measuring distances was invented: a light cart had a gear system connected to a wheel and a drum. Each li (576 m) was marked by the beat of a drum. With this invention the minister Pei Xiu created an 18-sheet Regional Atlas and a large map of China on silk, which was so large that it was difficult for one person to unfold it.
Exist Interesting Facts length measurements. So, for example, sailors measured their path tubes
, i.e. the distance the ship travels during the time it takes the sailor to smoke a pipe. In Spain there was a similar unit cigar
, and in Japan - horse shoe
(a straw sole that replaced a horseshoe). There were also Steps
(among the ancient Romans), and arshins
(?71 cm), and span (?18 cm). Therefore, the ambiguity of the measurement results showed the need to introduce a consistent unit. Really, inch
(2.54 cm, entered as thumb length, from the verb "inch") and foot
(30 cm, like the length of the foot from the English “foot” - foot) was difficult to compare.
Fig.1. The meter as a standard of length from 1889 to 1960
From 1889 to 1960, one ten-millionth of the distance measured along the Paris meridian from North Pole to the equator, - meter
(from the Greek metron - measure) (Fig. 1).
A rod made of platinum-yriadium alloy was used as a length standard; it was stored in Sèvres, near Paris. Until 1983, a meter was considered to be equal to 1650763.73 wavelengths of the orange spectral line emitted by a krypton lamp.
The discovery of the laser (in 1960 in the USA) made it possible to measure the speed of light with a greater degree of accuracy (?с=299,792,458 m/s) compared to the krypton lamp.
Meter
– unit of length equal to the distance that light travels in a vacuum in time? 99,792,458 pp.
The range of measuring the size of objects in nature is shown in Figure 2.
Fig.2. Range of measuring the size of objects in nature
Methods for measuring distances. To measure relatively small distances and sizes of bodies, a tape measure, ruler, or meter are used. If the measured volumes are small and greater accuracy is required, then measurements are carried out with a micrometer or caliper. When measuring large distances use different methods: triangulation, radar. For example, the distance to any star or moon is measured using the method triangulation (Fig. 3).
Fig.3. Triangulation method
Knowing the base - distance l between two telescopes located at points A and B on Earth, and the angles a1 And a2, under which they are directed towards the Moon, you can find the distances AC and BC:
When determining the distance to a star, the diameter of the Earth's orbit around the Sun can be used as a base (Fig. 4).
Fig.4. Determining the distance to a star
Currently, the distance of the planets closest to Earth is measured using the method laser ranging . A laser beam sent, for example, towards the Moon is reflected and, returning to Earth, is received by a photocell (Fig. 5).
Rice. 5. Measuring distances using laser ranging
By measuring the time interval t0 after which the reflected beam returns, and knowing the speed of light “c”, you can find the distance to the planet: .
To measure small distances using a conventional microscope, you can divide a meter into a million parts and get micrometer, or micron. However, it is impossible to continue division in this way, since objects whose dimensions are less than 0.5 microns cannot be seen with a regular microscope.
Fig.6. An ion microscope photograph of carbon atoms in graphite
Ion microscope (Fig. 6) makes it possible to measure the diameter of atoms and molecules of the order of 10~10 m. The distance between atoms is 1.5?10~10m. Intraatomic space is virtually empty, with a tiny nucleus at the center of the atom. Observing the scattering of high-energy particles as they pass through a layer of matter makes it possible to probe the material down to the size atomic nuclei(10–15m).
2. TIME. MEASUREMENT OF DIFFERENT TIME TERMS
Time is a measure of measuring different periods of time
. It is a measure of the speed at which any change occurs, i.e. a measure of the speed of events. Time measurement is based on periodic, repeating cyclic processes.
It is believed that the first clock was gnomon
, invented in China in late XVI century. Time was measured by the length and direction of the shadow from a vertical pole (gnomon) illuminated by the sun. This shadow indicator served as the first clock.
It has long been noted that astronomical phenomena have the greatest stability and repeatability; Day gives way to night and the seasons alternate regularly. All these phenomena are associated with the movement of the Sun on the celestial sphere. The calendar was created on their basis.
Measurements small gaps time (about 1 hour) remained a difficult task for a long time, which the Dutch scientist brilliantly coped with Christiaan Huygens(Fig. 7).
Fig.7. Christiaan Huygens
In 1656, he designed a pendulum clock, the oscillations of which were supported by a weight and the error of which was 10 s per day. But despite the constant improvement of clocks and the increasing accuracy of time measurement, the second (defined as 1/86400 of a day) could not be used as a constant standard of time. This is explained by a slight slowdown in the speed of rotation of the Earth around its axis and a corresponding increase in the period of revolution, i.e. duration of the day.
Obtaining a stable time standard was possible as a result of studying the emission spectra of different atoms and molecules, which made it possible to measure time with unique accuracy. The period of electromagnetic oscillations emitted by atoms is measured with a relative error of the order of 10–10 s (Fig. 8).
Fig.8. Time measurement range for objects in the Universe
In 1967, a new standard second was introduced. A second is a unit of time equal to 9,192,631,770 periods of radiation from the isotope of the cesium atom - 133.
Cesium-133 radiation is easily reproduced and measured in laboratory conditions. The error of such " atomic clock"for a year is 3*10-7 s.
To measure a longer period of time, a different kind of periodicity is used. Numerous studies of radioactive (decaying over time) isotopes have shown that the time during which their number decreases by 2 times (half life), is a constant value. This means that the half-life allows you to choose the time scale.
The choice of isotope for measuring time depends on the approximate time interval being measured. The half-life should be commensurate with the expected time interval (Table 1).
Table 1
Half-life of some isotopes
In archaeological research, the most commonly measured is the carbon isotope 14C, which has a half-life of 5,730 years. The age of the ancient manuscript is estimated at 5730 years, if the 14C content in it is 2 times less than the original (which is known). When the 14C content decreases by 4 times compared to the original, the age of the object is a multiple of two half-lives, i.e., equal to 11,460 years. To measure even longer periods of time, other radioactive isotopes that have longer half-lives are used. The uranium isotope 238U (half-life 4.5 billion years) turns into lead as a result of decay. Comparison of the content of uranium and lead in rocks and ocean water made it possible to establish the approximate age of the Earth, which is about 5.5 billion years.
3. WEIGHT
If length and time are fundamental characteristics of time and space, then mass is a fundamental characteristic of matter. All bodies have mass: solid, liquid, gaseous; different in size (from 10–30 to 1050 kg), shown in Fig. 9.
Fig.9. Range of measurement of the mass of objects in the Universe
Mass characterizes equal properties matter.
A person remembers the mass of bodies in a variety of situations: when buying groceries, in sports games, construction... - in all types of activities there is a reason to inquire about the mass of a particular body. Mass is no less a mysterious quantity than time. The standard of mass of 1 kg, since 1884, has been a platinum-iridium cylinder stored in the International Chamber of Weights and Measures near Paris. National chambers of weights and measures have copies of such a standard.
A kilogram is a unit of mass equal to the mass of the international standard kilogram.
Kilogram
(from French words kilo – thousand and gramme – small measure). A kilogram is approximately equal to the mass of 1 liter clean water at 15 0 C.
Working with a real mass standard requires special care, since the touch of forceps and even the impact atmospheric air may lead to a change in the mass of the standard. Determination of the mass of objects having a volume commensurate with the volume of the mass standard can be carried out with a relative error of the order of 10–9 kg.
4. PHYSICAL DEVICES
Physical instruments are used to conduct various types of research and experiments. As physics developed, they improved and became more complex (see. Application
).
Some physical instruments are very simple, for example a ruler (Fig. 10), a plumb line (a weight suspended on a thread) that allows you to check the verticality of structures, a level, a thermometer, a stopwatch, a current source; electric motor, relay, etc.
Fig. 10. Ruler
Scientific experiments often use complex instruments and installations, which have improved and become more complex as science and technology have developed. Thus, to study the properties of elementary particles that make up a substance, they use accelerators - huge, complex installations equipped with many different measuring and recording instruments. In accelerators, particles are accelerated to enormous speeds, close to the speed of light, and become “projectiles” bombarding matter placed in special chambers. The phenomena that occur during this process allow us to draw conclusions about the structure of atomic nuclei and elementary particles. Large accelerator created in 1957 V The city of Dubna near Moscow has a diameter of 72 m, and the accelerator in the city of Serpukhov has a diameter of 6 km (Figure 11).
Fig. 11. Accelerator
When performing astronomical observations, various instruments are used. The main astronomical instrument is the telescope. It allows you to get an image of the sun, moon, planets.
5. METRIC INTERNATIONAL SYSTEM OF UNITS "SI"
They measure everything: doctors determine the patients’ body temperature, lung capacity, height, and pulse; sellers weigh products, measure out meters of fabric; tailors take measurements from fashionistas; musicians strictly maintain rhythm and tempo, counting bars; pharmacists weigh powders and measure into bottles required amount medicines; physical education teachers do not part with a tape measure and a stopwatch, determining the outstanding sports achievements of schoolchildren... All inhabitants of the planet measure, estimate, evaluate, compare, count, distinguish, measure, measure and count, count, count...
Each of us, without a doubt, knows that before we measure, we need to establish “the unit with which you will compare the measured distance, or period of time, or mass.”
Another thing is clear: the whole world needs to agree on units, otherwise unimaginable confusion will arise. In games, misunderstandings are also possible: one’s step is much shorter, another’s is longer (Example: “We will take a penalty from seven steps”). Scientists around the world prefer to work with a consistent and logically consistent system of units of measurement. At the General Conference of Weights and Measures in 1960, agreement was reached on the international system of units - Systems International d "Unite"s (abbreviated as "SI units"). This system includes seven basic units
measurement, and all other units of measurement derivatives
are derived from the basic ones by multiplying or dividing one unit by another without numerical conversions (Table 2).
table 2
Basic units of measurement "SI"
The international system of units is metric . This means that multiples and submultiples are always formed from basic units in the same way: by multiplying or dividing by 10. This is convenient, especially when writing very large and very small numbers. For example, the distance from the Earth to the Sun, approximately equal to 150,000,000 km, can be written as follows: 1.5 * 100,000,000 km. Now let’s replace the number 100,000,000 with 108. Thus, the distance to the Sun is written as:
1.5 * 10 8 km = l.5 * 10 8 * 10 3 M = l.5 * 10 8 + 3 m = l.5 * 10 11 m.
Another example.
The diameter of a hydrogen molecule is 0.00000002 cm.
Number 0.00000002 = 2/100.000.000 = 2/10 8. For multiplicity, the number 1/10 8 is written in the form 10 –8. So, the diameter of a hydrogen molecule is 2*10 –8 cm.
But depending on the measurement range, it is convenient to use units that are larger or smaller in size. These multiples
And lobar
units differ from the basic ones by orders of magnitude. The name of the main quantity is the root of the word, and the prefix characterizes the corresponding difference in order.
For example, the prefix “kilo-” means introducing a unit a thousand times (3 orders of magnitude) larger than the base one: 1 km = 10 3 m.
Table 3 shows prefixes for the formation of multiples and submultiples.
Table 3
Prefixes for forming decimal multiples and submultiples
Degree |
Console |
Symbol |
Examples |
Degree |
Console |
Symbol |
Examples |
exajoule, EJ |
decibel, dB |
||||||
petasecond, Ps |
centimeter, cm |
||||||
terahertz, THz |
millimeter, mm |
||||||
gigavolt, GV |
microgram, mcg |
||||||
megawatt, MW |
nanometer, nm |
||||||
kilogram, kg |
10 –12 |
picofarad, pF |
|||||
hectopascal, hPa |
10 –15 |
femtometer, fm |
|||||
decatesla, dT |
10 –18 |
attocoulomb, aCl |
The multiples and submultiples introduced in this way often characterize physical objects in order of magnitude.
Many physical quantities are constant - constants
(from the Latin word constants- constant, unchanging) (Table 4). For example, the melting temperature of ice and the boiling temperature of water, the speed of light propagation, and the densities of various substances are constant under these conditions. The constants are carefully measured in scientific laboratories and entered into the tables of reference books and encyclopedias. Lookup tables are used by scientists and engineers.
Table 4
Fundamental Constants
Constant |
Designation |
Meaning |
Speed of light in vacuum |
2.998 * 10 8 m/s |
|
Planck's constant |
6.626 * 10 –34 J*s |
|
Electron charge |
1.602 * 10 –19 C |
|
Electrical constant |
8.854 * 10 –12 Cl 2 / (N * m2) |
|
Faraday's constant |
9.648 * 10 4 C/mol |
|
Magnetic permeability of vacuum |
4 * 10 –7 Wb/(A*m) |
|
Atomic mass unit |
1.661 * 10 –27 kg |
|
Boltzmann's constant |
1.38 * 10 –23 J/K |
|
Avogadro's constant |
6.02 * 10 23 mol–1 |
|
Molar gas constant |
8.314 J/(mol*K) |
|
Gravitational constant |
6.672 * 10 –11 N * m2/kg2 |
|
Electron mass |
9.109 * 10 –31 kg |
|
Proton mass |
1.673 * 10 –27 kg |
|
Neutron mass |
1.675 * 10 –27 kg |
6. NON-METRIC RUSSIAN UNITS
They are shown in Table 5.
Table 5
Non-metric Russian units
Quantities |
Units |
Value in SI units, multiples and submultiples thereof |
| mile (7 versts) | ||
| verst (500 fathoms) | ||
| fathom (3 arshins; 7 pounds; 100 acres) | ||
| weave | ||
| arshin (4 quarters; 16 vershok; 28 inches) | ||
| quarter (4 inches) | ||
| inch | ||
| ft (12 in) | 304.8 mm (exact) |
|
| inch (10 lines) | 25.4 mm (exact) |
|
| line (10 points) | 2.54 mm (exact) |
|
| dot | 254 microns (exactly) |
|
| square layout | ||
| tithe | ||
| square fathom | ||
| cubic fathom | ||
| cubic arshin | ||
| cubic vershok | ||
Capacity |
bucket | |
| quarter (for bulk solids) | ||
| quadruple (8 garnets; 1/8 quarter) | ||
| garnets | ||
| Berkovets (10 poods) | ||
| pood (40 pounds) | ||
| pound (32 lots; 96 spools) | ||
| lot (3 spools) | ||
| spool (96 shares) | ||
| share | ||
Strength, weight |
Berkovets (163.805 kgf) | |
| pood (16.3805 kgf) | ||
| lb (0.409512 kgf) | ||
| lot (12.7973 gs) | ||
| spool (4.26575 gf) | ||
| share (44.4349 mgs) |
* The names of Russian units of force and weight coincided with the names of Russian units of mass.
7. MEASUREMENT OF PHYSICAL QUANTITIES
Practically, any experiment, any observation in physics is accompanied by the measurement of physical quantities. Physical quantities are measured using special instruments. Many of these devices are already known to you. For example, a ruler (Fig. 7). Can be measured linear dimensions bodies: length, height and width; clock or stopwatch - time; using lever scales, the mass of the body is determined by comparing it with the mass of the weight taken as a unit of mass. A beaker allows you to measure volumes of liquid or granular bodies (substances).
Usually the device has a scale with lines. The distances between two lines, near which the values of a physical quantity are written, can be additionally divided into several divisions, not indicated by numbers. Divisions (spaces between strokes) and numbers are the scale of the device. On the instrument scale, as a rule, there is a unit of quantity (name) in which the physical quantity being measured is expressed. In the case when the numbers do not stand opposite each stroke, the question arises: how to find out the numerical value of the measured value if it cannot be read on the scale? To do this you need to know scale division price – the value of the smallest scale division of the measuring device.
When selecting instruments for measurements, it is important to consider the measurement limits. Most often, there are devices with only one - the upper limit of measurement. Sometimes there are two-limit devices. For such devices, the zero division is located inside the scale.
Let’s imagine that we are driving in a car, and the speedometer needle stops opposite the “70” mark. Can you be sure that the speed of the car is exactly 70 km/h? No, because the speedometer has an error. You can, of course, say that the speed of the car is approximately 70 km/h, but this is not enough. For example, braking distances the car depends on the speed, and its “approximateness” can lead to an accident. Therefore, the manufacturer determines the highest speedometer error and indicates it in the passport of this device. The speedometer error value allows you to determine within what limits the true value of the vehicle speed lies.
Let the speedometer error indicated in the passport be 5 km/h. In our example, let’s find the difference and the sum of the speedometer reading and its error:
70 km/h – 5 km/h = 65 km/h.
70 km/h + 5 km/h = 75 km/h.
Without knowing the true speed value, we can be sure that the car's speed is not less than 65 km/h and not more than 75 km/h. This result can be written using the signs " < " (less than or equal to) and " > "(greater than or equal to): 65 km/h < car speed < 75 km/h.
The fact that when the speedometer shows 70 km/h, the true speed may turn out to be 75 km/h must be taken into account. For example, research has shown that if a car moves on wet asphalt at a speed of 70 km/h, its braking distance does not exceed 46 m, and at a speed of 75 km/h the braking distance increases to 53 m.
The given example allows us to draw the following conclusion: all instruments have an error; as a result of measurement, it is impossible to obtain the true value of the measured value. You can only indicate the interval in the form of an inequality to which the unknown value of a physical quantity belongs.
To pass the boundaries of this inequality, it is necessary to know the error of the device.
X- etc < X< X+ etc.
Measurement error X The error of the device is never less than approx.
Often the instrument pointer does not coincide with the scale line. Then it is very difficult to determine the distance from the stroke to the pointer. Here is another reason for the error called counting error
. This reading error, for example, for a speedometer, does not exceed half the division value.
The reference book contains data on the mechanical, thermodynamic and molecular-kinetic properties of substances, electrical properties of metals, dielectrics and semiconductors, magnetic properties of dia-, para- and ferromagnets, optical properties of substances, including laser ones, optical, X-ray and Mössbauer spectra, neutron physics, thermonuclear reactions, as well as geophysics and astronomy.
The material is presented in the form of tables and graphs, accompanied by brief explanations and definitions of the relevant quantities. For ease of use, units of measurement of physical quantities are given in various systems and conversion factors.
Development physical sciences In recent decades, it has been characterized by an uncontrollable increase in the flow of information. This information needs systematic generalization and concentration. Tables of physical quantities naturally concentrate that part of the flow of information that allows for numerical expression.
Specialized reference books and tables have been and continue to be published on certain narrow branches of physics. Specialists usually turn to such publications.
The proposed tables are intended for a wide range of readers who need to obtain information from areas of physics that lie outside their more or less narrow specialty. Therefore, in the proposed tables the reader will not find, for example, detailed data either on the spectra of elements, or on the properties of solutions, etc. “Tables of Physical Quantities” do not pretend to compete with such multi-volume publications as the famous Landolt-Bornstein reference book or Technical Tables and etc. For everyday use, a widely available reference book of moderate length is usually required. The tables offered to the reader are intended to satisfy this need.
The compilers understand that the tables are far from perfect, and hope that readers will contribute to the improvement of this book in subsequent editions with their critical comments.
TABLE OF CONTENTS
From the editor
I. GENERAL SECTION
Chapter 1. Units of measurement of physical quantities
Chapter 2. Fundamental physical constants
Chapter 3. Periodic table elements
II. MECHANICS AND THERMODYNAMICS
Chapter 4. Mechanical properties materials
Chapter 5. Density of substances
Chapter 6. Compressibility of substances
Chapter 7. Acoustics
Chapter 8. Thermometry
Chapter 9. Temperature expansion coefficients and the Joule-Thomson effect
Chapter 10. Heat capacity
Chapter 11. Phase transitions, melting and boiling
Chapter 12. Vapor pressure of various substances
Chapter 13. Critical parameters of substances and virial coefficients
Chapter 14. Surface Tension Coefficient
III. KINETIC PHENOMENA
Chapter 15. Thermal conductivity
Chapter 16. Viscosity
Chapter 17. Diffusion of atoms and molecules
Chapter 18. Effective sizes of atoms and ions
IV. ELECTRICITY AND MAGNETISM
Chapter 19. Electrical properties of metals and alloys
Gland 20. Electrical properties of dielectrics
Chapter 21. Electrical properties of semiconductors
Chapter 22. Ionization potentials and dissociation energies
Chapter 23. Gas discharge
Chapter 24. Electronic emission
Chapter 25. Thermoelectric phenomena
Chapter 27. Magnetic properties of dia- and paramagnets
Chapter 28. Magnetic properties of ferromagnets
Chapter 29. Ferrites
Chapter 30. Antiferromagnets
V. OPTICS AND X-RAY
Chapter 31. Optical properties of matter
Chapter 32. Spectra of elements and some parameters of molecules
Chapter 33. Lasers
Chapter 34. Electro-, magneto- and piezo-optical effects
Chapter 35. X-ray radiation
VI. NUCLEAR PHYSICS
Chapter 36. Elementary particles
Chapter 37. Nuclear properties of nuclides
Chapter 38. Mössbauer nuclei
Chapter 39. Reactions under the influence of neutrons
Chapter 40. Reactions leading to the formation of neutrons
Chapter 41. The passage of neutrons through matter
Chapter 42. Nuclear fission
Chapter 43. Thermonuclear reactions
Chapter 44. Passage of ionizing radiation through matter
Chapter 45. Cosmic radiation
VII. ASTRONOMY AND GEOPHYSICS
Chapter 46. Astronomy and astrophysics
Chapter 47. Geophysics
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