8. True, actual and measured value of a physical quantity.
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.
True value of a physical quantity- 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.
Real value of a physical quantity- this is a value of a quantity found experimentally and so close to the true value that for a given purpose it can be used instead.
Measured value of a physical quantity- 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 level from hot air balloon or measuring constant voltage of 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.
Based on 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
Physical quantities
Physical quantity– this is a characteristic of physical objects or phenomena material world, common for many objects or phenomena in a qualitative sense, but individual in a quantitative sense for each of them. For example, mass, length, area, temperature, etc.
Each physical quantity has its own qualitative and quantitative characteristics .
Qualitative characteristics is determined by what property of a material object or what feature of the material world this quantity characterizes. Thus, the property “strength” quantitatively characterizes materials such as steel, wood, fabric, glass and many others, while the quantitative value of strength for each of them is completely different
To identify the quantitative difference in the content of a property in any object, reflected by a physical quantity, the concept is introduced physical quantity size . This size is set during the process measurements- a set of operations performed to determine the quantitative value of a quantity (Federal Law “On Ensuring the Uniformity of Measurements”
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.). Between the sizes of each physical quantity there are relationships in the form of numerical forms (such as “more”, “less”, “equality”, “sum”, etc.), which can serve as a model of this quantity.
Depending on the degree of approximation to objectivity, they distinguish true, actual and measured values of a physical quantity .
The true value of a physical quantity is 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.
The actual value of a physical quantity is this is a value of a quantity found experimentally and so close to the true value that it can be used instead for a given purpose.
Measured value of a physical quantity - this is the value obtained by measurement using specific methods and measuring instruments.
When planning measurements, one should strive to ensure that the range of measured quantities meets the requirements of the measurement task (for example, during control, the measured quantities must reflect the corresponding indicators of product quality).
For each product parameter the following requirements must be met:
The correctness of the formulation of the measured value, excluding the possibility different interpretations(for example, it is necessary to clearly define in what cases the “mass” or “weight” of the product, the “volume” or “capacity” of the vessel, etc. is determined);
The certainty of the properties of the object to be measured (for example, “the temperature in the room is not more than ... ° C” allows for the possibility of different interpretations. It is necessary to change the wording of the requirement so that it is clear whether this requirement is established for the maximum or average temperature of the room, which will be in further taken into account when performing measurements);
Use of standardized terms.
A physical quantity that, by definition, is assigned a numerical value equal to one is called unit of physical quantity.
Many units of physical quantities are reproduced by measures used for measurements (for example, meter, kilogram). On early stages development of material culture (in slave-holding and feudal societies), there were units for a small range of physical quantities - length, mass, time, area, volume. Units of physical quantities were chosen without connection with each other, and, moreover, different in different countries and geographical areas. This is how a large number of often identical in name, but different in size units arose - elbows, feet, pounds.
As trade relations between peoples expanded and science and technology developed, the number of units of physical quantities increased and the need for unification of units and the creation of systems of units was increasingly felt. Special international agreements began to be concluded on units of physical quantities and their systems. In the 18th century In France, the metric system of measures was proposed, which later received international recognition. On its basis, a number of metric systems of units were built. Currently, further ordering of units of physical quantities is taking place on the basis of the International System of Units (SI).
Units of physical quantities are divided into systemic, i.e., those included in any system of units, and non-systemic units (for example, mmHg, horsepower, electron-volt).
System units physical quantities are divided into basic, chosen arbitrarily (meter, kilogram, second, etc.), and derivatives, formed by equations of connection between quantities (meter per second, kilogram per cubic meter, newton, joule, watt, etc.).
For the convenience of expressing quantities many times larger or smaller than units of physical quantities, we use multiples of units (for example, kilometer - 10 3 m, kilowatt - 10 3 W) and submultiples (for example, a millimeter is 10 -3 m, a millisecond is 10-3 s)..
In metric systems of units, multiples and fractional units of physical quantities (except for units of time and angle) are formed by multiplying the system unit by 10 n, where n is a positive or negative integer. Each of these numbers corresponds to one of the decimal prefixes adopted to form multiples and units.
In 1960, at the XI General Conference on Weights and Measures of the International Organization of Weights and Measures (IIOM), the International System of Weights and Measures was adopted units(SI).
Basic units in the international system of units are: meter (m) – length, kilogram (kg) – mass, second (s) – time, ampere (A) – strength electric current, kelvin (K) – thermodynamic temperature, candela (cd) – luminous intensity, mole – amount of substance.
Along with systems of physical quantities, so-called non-systemic units are still used in measurement practice. These include, for example: units of pressure - atmosphere, millimeter of mercury, unit of length - angstrom, unit of heat - calorie, units of acoustic quantities - decibel, background, octave, units of time - minute and hour, etc. However, in Currently, there is a tendency to reduce them to a minimum.
The international system of units has a number of advantages: universality, unification of units for all types of measurements, coherence (consistency) of the system (coefficients of proportionality in physical equations are dimensionless), better mutual understanding between various specialists in the process of scientific, technical and economic relations between countries.
Currently, the use of units of physical quantities in Russia is legalized by the Constitution of the Russian Federation (Article 71) (standards, standards, the metric system and time calculation are under the jurisdiction of Russian Federation) And federal law"On ensuring the uniformity of measurements." Article 6 of the Law determines the use in the Russian Federation of units of quantities of the International System of Units adopted by the General Conference on Weights and Measures and recommended for use by the International Organization of Legal Metrology. At the same time, in the Russian Federation, non-system units of quantities, the name, designation, rules of writing and application of which are established by the Government of the Russian Federation, can be accepted for use on an equal basis with SI units of quantities.
IN practical activities should be guided by units of physical quantities regulated by GOST 8.417-2002 “ State system ensuring uniformity of measurements. Units of quantities."
Standard along with mandatory use basic and derivatives units of the International System of Units, as well as decimal multiples and submultiples of these units, it is allowed to use some units that are not included in the SI, their combinations with SI units, as well as some decimal multiples and submultiples of the listed units that are widely used in practice.
The standard defines the rules for the formation of names and designations of decimal multiples and submultiples of SI units using multipliers (from 10 –24 to 10 24) and prefixes, the rules for writing unit designations, the rules for the formation of coherent derived SI units
Factors and prefixes used to form the names and designations of decimal multiples and submultiples of SI units are given in Table.
Factors and prefixes used to form the names and designations of decimal multiples and submultiples of SI units
| Decimal multiplier | Console | Prefix designation | Decimal multiplier | Console | Prefix designation | ||
| intl. | rus | intl. | russ | ||||
| 10 24 | iotta | Y | AND | 10 –1 | deci | d | d |
| 10 21 | zetta | Z | Z | 10 –2 | centi | c | With |
| 10 18 | exa | E | E | 10 –3 | Milli | m | m |
| 10 15 | peta | P | P | 10 –6 | micro | µ | mk |
| 10 12 | tera | T | T | 10 –9 | nano | n | n |
| 10 9 | giga | G | G | 10 –12 | pico | p | P |
| 10 6 | mega | M | M | 10 –15 | femto | f | f |
| 10 3 | kilo | k | To | 10 –18 | atto | a | A |
| 10 2 | hecto | h | G | 10 –21 | zepto | z | h |
| 10 1 | soundboard | da | Yes | 10 –24 | iocto | y | And |
Coherent derived units The International System of Units, as a rule, is formed using the simplest equations of connections between quantities (defining equations), in which the numerical coefficients are equal to 1. To form derived units, the designations of quantities in the connection equations are replaced by the designations of SI units.
If the coupling equation contains a numerical coefficient different from 1, then to form a coherent derivative of an SI unit, the notation of quantities with values in SI units is substituted into the right side, giving, after multiplication by the coefficient, a total numerical value equal to 1.
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. Physical quantity is scientific characteristics 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 qualitative terms 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 administered. 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 an 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. 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. Absence 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 ٠К -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 correspond to a specific 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.
Physics, as we have already established, studies general patterns in the world around us. To do this, scientists conduct observations of physical phenomena. However, when describing phenomena, it is customary to use not everyday language, but special words that have a strictly defined meaning - terms. You have already encountered some physical terms in the previous paragraph. Many terms you just have to learn and remember their meanings.
In addition, physicists need to describe various properties (characteristics) of physical phenomena and processes, and characterize them not only qualitatively, but also quantitatively. Let's give an example.
Let's study the dependence of the time of falling of a stone from the height from which it falls. Experience shows: the greater the height, the longer the fall time. This is a qualitative description; it does not allow us to describe the result of the experiment in detail. To understand the pattern of such a phenomenon as falling, you need to know, for example, that when the height increases four times, the time it takes for a stone to fall usually doubles. This is an example of quantitative characteristics of the properties of a phenomenon and the relationship between them.
In order to quantitatively describe the properties (characteristics) of physical objects, processes or phenomena, physical quantities are used. Examples of physical quantities known to you are length, time, mass, speed.
Physical quantities quantitatively describe the properties of physical bodies, processes, and phenomena.
You have come across some quantities before. In mathematics lessons, when solving problems, you measured the lengths of segments and determined the distance traveled. In this case, you used the same physical quantity - length. In other cases, you found the duration of movement of various objects: a pedestrian, a car, an ant - and also used only one physical quantity for this - time. As you have already noticed, for different objects the same physical quantity takes different meanings. For example, the lengths of different segments may not be the same. Therefore, the same value can take different meanings and be used to characterize a wide variety of objects and phenomena.
The need to introduce physical quantities also lies in the fact that the laws of physics are written with their help.
In formulas and calculations, physical quantities are denoted by Latin letters and greek alphabets. There are generally accepted designations, for example, length - l or L, time - t, mass - m or M, area - S, volume - V, etc.
If you write down the value of a physical quantity (the same length of a segment, obtained as a result of measurement), you will notice: this value is not just a number. Having said that the length of the segment is 100, it is necessary to clarify in what units it is expressed: in meters, centimeters, kilometers or something else. Therefore, they say that the value of a physical quantity is a named number. It can be represented as a number followed by the name of the unit of this quantity.
The value of a physical quantity = Number * Unit of quantity.
The units of many physical quantities (for example, length, time, mass) originally arose from the needs everyday life. For them, different units were invented at different times by different peoples. It is interesting that the names of many units of quantities have different nations are the same because the measurements of the human body were used when selecting these units. For example, a unit of length called a "cubit" was used in Ancient Egypt, Babylon, the Arab world, England, Russia.
But length was measured not only in cubits, but also in vershoks, feet, leagues, etc. It should be said that even with the same names, units of the same size were different among different peoples. In 1960, scientists developed International system units (SI, or SI). This system has been adopted by many countries, including Russia. Therefore, the use of units of this system is mandatory.
It is customary to distinguish between basic and derived units of physical quantities. In SI, the basic mechanical units are length, time and mass. Length is measured in meters (m), time in seconds (s), mass in kilograms (kg). Derived units are formed from basic ones using relationships between physical quantities. For example, the unit of area is square meter(m 2) - equal to the area of a square with a side length of one meter.
When measuring and calculating, we often have to deal with physical quantities, numerical values which differ many times from the unit value. In such cases, a prefix is added to the name of the unit, meaning multiplication or division of the unit by a certain number. Very often they use the multiplication of the accepted unit by 10, 100, 1000, etc. (multiple values), as well as the division of the unit by 10, 100, 1000, etc. (multiple values, i.e. fractions). For example, a thousand meters is one kilometer (1000 m = 1 km), the prefix is kilo-.
Prefixes meaning multiplication and division of units of physical quantities by ten, hundred and thousand are given in Table 1.
Results
A physical quantity is a quantitative characteristic of the properties of physical objects, processes or phenomena.
A physical quantity characterizes the same property of a wide variety of physical objects and processes.
The value of a physical quantity is a named number.
The value of a physical quantity = Number * Unit of quantity.
Questions
- What are physical quantities used for? Give examples of physical quantities.
- Which of the following terms are physical quantities and which are not? Ruler, car, cold, length, speed, temperature, water, sound, mass.
- How are the values of physical quantities written?
- What is SI? What is it for?
- Which units are called basic and which are derivative? Give examples.
- The body mass is 250 g. Express the mass of this body in kilograms (kg) and milligrams (mg).
- Express the distance 0.135 km in meters and millimeters.
- In practice, a non-system unit of volume is often used - liter: 1 l = 1 dm 3. In SI, the unit of volume is called the cubic meter. How many liters are in one cubic meter? Find the volume of water contained in a cube with an edge of 1 cm, and express this volume in liters and cubic meters, using the necessary prefixes.
- Name the physical quantities that are necessary to describe the properties of such a physical phenomenon as wind. Use what you learned in science class as well as your observations. Plan a physics experiment to measure these quantities.
- What ancient and modern units of length and time do you know?
