Units. Petroleum chemistry Mechanical and thermal units
How is vibration measured?
For a quantitative description of the vibration of rotating equipment and for diagnostic purposes, vibration acceleration, vibration velocity and vibration displacement are used.
Vibration acceleration
Vibration acceleration is the value of vibration directly related to the force that caused the vibration. Vibration acceleration characterizes the power dynamic interaction of elements inside the unit, which caused this vibration. Usually displayed by amplitude (Peak) - the maximum modulo value of acceleration in the signal. The use of vibration acceleration is theoretically ideal, since the piezoelectric sensor (accelerometer) measures exactly the acceleration and it does not need to be specially converted. The disadvantage is that there are no practical developments for it in terms of norms and threshold levels, there is no generally accepted physical and spectral interpretation of the features of the manifestation of vibration acceleration. It is successfully used in the diagnosis of defects that have a shock nature - in rolling bearings, gearboxes.
Vibration acceleration is measured in:
- meters per second squared [m/s 2 ]
- G, where 1G \u003d 9.81 m / s 2
- decibels, a level of 0 dB should be indicated. If not specified, then the value is taken as 10 -6 m/s 2
How to convert vibration acceleration to dB?
For standard level 0 dB = 10 -6 m/s 2:
AdB = 20 * lg10(A) + 120
AdB - vibration acceleration in decibels
A - vibration acceleration in m/s 2
120 dB - level 1 m/s 2
Vibration velocity
Vibration velocity is the speed of movement of the controlled point of the equipment during its precession along the measurement axis.
In practice, it is usually not the maximum value of the vibration velocity that is measured, but its root mean square value, RMS (RMS). The physical essence of the vibration velocity RMS parameter is the equality of the energy impact on the machine supports of a real vibration signal and a fictitious constant, numerically equal in value to the RMS. The use of the RMS value is also due to the fact that earlier vibration measurements were carried out by pointer instruments, and they are all integrating by the principle of operation, and show exactly the root-mean-square value of the alternating signal.
Of the two representations of vibration signals widely used in practice (vibration velocity and vibration displacement), it is preferable to use vibration velocity, since this is a parameter that immediately takes into account both the displacement of the controlled point and the energy impact on the supports from the forces that caused vibration. The information content of vibration displacement can be compared with the information content of vibration velocity only if, in addition, in addition to the amplitude of oscillations, the frequencies of both the entire oscillation and its individual components are taken into account. In practice, this is very difficult to do.
To measure RMS vibration velocity are used. In more complex devices (vibration analyzers) there is always a vibrometer mode.
Vibration velocity is measured in:
- millimeters per second [mm/s]
- inches per second : 1 in/s = 25.4 mm/sec
- decibels, a level of 0 dB should be indicated. If not specified, then the value is taken 5 * 10 -5 mm / s
How to convert vibration velocity to dB?
For standard level 0 dB = 5 * 10 -5 mm/s:
VdB = 20 * lg10(V) + 86
VdB - vibration velocity in decibels
lg10 - Decimal logarithm (logarithm base 10)
V – vibration velocity in mm/s
86 dB - level 1 mm/s
Below are the values of vibration velocity in dB for . It can be seen that the difference between neighboring values is 4 dB. This corresponds to a difference of 1.58 times.
| mm/s | dB |
| 45 | 119 |
| 28 | 115 |
| 18 | 111 |
| 11,2 | 107 |
| 7,1 | 103 |
| 4,5 | 99 |
| 2,8 | 95 |
| 1,8 | 91 |
| 1,12 | 87 |
| 0,71 | 83 |
vibration displacement
Vibration displacement (vibration displacement, displacement) shows the maximum limits of movement of the controlled point during the vibration process. Usually displayed as a swing (peak-to-peak, peak-to-peak). Vibration displacement is the distance between the extreme points of movement of an element of rotating equipment along the measurement axis.
This guide has been compiled from various sources. But its creation was prompted by a small book "Mass Radio Library" published in 1964, as a translation of the book by O. Kroneger in the GDR in 1961. Despite its antiquity, it is my reference book (along with several other reference books). I think time has no power over such books, because the foundations of physics, electrical and radio engineering (electronics) are unshakable and eternal.
Units of measurement of mechanical and thermal quantities.
Units of measurement of electromagnetic quantities
|
Relations between units of magnetic quantities
in CGSM and SI systems
| In electrical and reference literature published before the introduction of the SI system, the magnitude of the magnetic field strength H often expressed in oersteds (uh) magnetic induction value AT - in gauss (gs), magnetic flux Ф and flux linkage ψ - in maxwells (µs). |
| 1e \u003d 1/4 π × 10 3 a / m; 1a / m \u003d 4π × 10 -3 e; 1gf=10 -4 t; 1tl=104 gs; 1mks=10 -8 wb; 1vb=10 8 ms |
| It should be noted that the equalities are written for the case of a rationalized practical MKSA system, which was included in the SI system as an integral part. From a theoretical point of view, it would be better to about in all six relationships, replace the equal sign (=) with the match sign (^). For example |
|
1e \u003d 1 / 4π × 10 3 a / m |
| which means: a field strength of 1 Oe corresponds to a strength of 1/4π × 10 3 a/m = 79.6 a/m |
| The point is that the units gs and ms belong to the CGMS system. In this system, the unit of current strength is not the main one, as in the SI system, but a derivative. Therefore, the dimensions of the quantities characterizing the same concept in the CGSM and SI systems turn out to be different, which can lead to misunderstandings and paradoxes, if you forget about this circumstance. When performing engineering calculations, when there is no basis for misunderstandings of this kind |
Off-system units
Some mathematical and physical concepts
applied to radio engineering
| Like the concept - the speed of movement, in mechanics, in radio engineering there are similar concepts, such as the rate of change of current and voltage. They can be either averaged over the course of the process, or instantaneous. |
|
i \u003d (I 1 -I 0) / (t 2 -t 1) \u003d ΔI / Δt |
| With Δt -> 0, we get the instantaneous values of the current change rate. It most accurately characterizes the nature of the change in the quantity and can be written as: |
|
i=lim ΔI/Δt =dI/dt |
| And you should pay attention - the average values and instantaneous values \u200b\u200bcan differ by dozens of times. This is especially evident when a changing current flows through circuits with a sufficiently large inductance. |
decibell |
| To assess the ratio of two quantities of the same dimension in radio engineering, a special unit is used - the decibel. |
| K u \u003d U 2 / U 1 Voltage gain; K u [dB] = 20 log U 2 / U 1 Voltage gain in decibels. Ki [dB] = 20 log I 2 / I 1 Current gain in decibels. Kp[dB] = 10 log P 2 / P 1 Power gain in decibels. |
| The logarithmic scale also allows, on a graph of normal sizes, to depict functions that have a dynamic range of parameter changes in several orders of magnitude. |
| To determine the signal strength in the reception area, another logarithmic unit of DBM is used - dicibells per meter. |
| P [dbm] = 10 log U 2 / R +30 = 10 log P + 30. [dbm]; |
| The effective load voltage at a known P[dBm] can be determined by the formula: |
 |
Dimensional coefficients of basic physical quantities
| In accordance with state standards, the following multiple and submultiple units - prefixes are allowed: | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
Viscosity is the most important physical constant characterizing the operational properties of boiler and diesel fuels, petroleum oils, and a number of other petroleum products. The value of viscosity is used to judge the possibility of atomization and pumpability of oil and oil products.
There are dynamic, kinematic, conditional and effective (structural) viscosity.
Dynamic (absolute) viscosity [μ ], or internal friction, is the property of real fluids to resist shear shear forces. Obviously, this property manifests itself when the fluid moves. Dynamic viscosity in the SI system is measured in [N·s/m 2 ]. This is the resistance that a liquid exerts during the relative movement of its two layers with a surface of 1 m 2, located at a distance of 1 m from each other and moving under the action of an external force of 1 N at a speed of 1 m / s. Considering that 1 N/m 2 = 1 Pa, dynamic viscosity is often expressed in [Pa s] or [mPa s]. In the CGS system (CGS), the dimension of dynamic viscosity is [dyn·s/m 2 ]. This unit is called poise (1 P = 0.1 Pa s).
Conversion factors for calculating the dynamic [ μ ] viscosity.
| Units | Micropoise (µP) | Centipoise (cP) | Poise ([g/cm s]) | Pa s ([kg/m s]) | kg/(m h) | kg s / m 2 |
| Micropoise (µP) | 1 | 10 -4 | 10 -6 | 10 7 | 3.6 10 -4 | 1.02 10 -8 |
| Centipoise (cP) | 10 4 | 1 | 10 -2 | 10 -3 | 3,6 | 1.02 10 -4 |
| Poise ([g/cm s]) | 10 6 | 10 2 | 1 | 10 3 | 3.6 10 2 | 1.02 10 -2 |
| Pa s ([kg/m s]) | 10 7 | 10 3 | 10 | 1 3 | 3.6 10 3 | 1.02 10 -1 |
| kg/(m h) | 2.78 10 3 | 2.78 10 -1 | 2.78 10 -3 | 2.78 10 -4 | 1 | 2.84 10 -3 |
| kg s / m 2 | 9.81 10 7 | 9.81 10 3 | 9.81 10 2 | 9.81 10 1 | 3.53 10 4 | 1 |
Kinematic viscosity [ν ] is the value equal to the ratio of the dynamic viscosity of the fluid [ μ ] to its density [ ρ ] at the same temperature: ν = μ/ρ. The unit of kinematic viscosity is [m 2 /s] - the kinematic viscosity of such a liquid, the dynamic viscosity of which is 1 N s / m 2 and the density is 1 kg / m 3 (N \u003d kg m / s 2). In the CGS system, kinematic viscosity is expressed in [cm 2 /s]. This unit is called stokes (1 St = 10 -4 m 2 / s; 1 cSt = 1 mm 2 / s).
Conversion factors for calculating the kinematic [ ν ] viscosity.
| Units | mm 2 /s (cSt) | cm 2 / s (St) | m 2 /s | m 2 / h |
| mm 2 /s (cSt) | 1 | 10 -2 | 10 -6 | 3.6 10 -3 |
| cm 2 / s (St) | 10 2 | 1 | 10 -4 | 0,36 |
| m 2 /s | 10 6 | 10 4 | 1 | 3.6 10 3 |
| m 2 / h | 2.78 10 2 | 2,78 | 2.78 10 4 | 1 |
Oils and petroleum products are often characterized conditional viscosity, which is taken as the ratio of the time of flow through the calibrated hole of a standard viscometer 200 ml of oil at a certain temperature [ t] by the time of the expiration of 200 ml of distilled water at a temperature of 20°C. Nominal viscosity at temperature [ t] is denoted by the sign of WU, and is expressed by the number of conventional degrees.
Relative viscosity is measured in degrees VU (°VU) (if the test is carried out in a standard viscometer according to GOST 6258-85), Saybolt seconds and Redwood seconds (if the test is carried out on Saybolt and Redwood viscometers).
You can transfer viscosity from one system to another using a nomogram.
In petroleum dispersed systems, under certain conditions, in contrast to Newtonian fluids, the viscosity is a variable dependent on the shear rate gradient. In these cases, oils and oil products are characterized by effective or structural viscosity:
For hydrocarbons, the viscosity essentially depends on their chemical composition: it increases with increasing molecular weight and boiling point. The presence of side branches in the molecules of alkanes and naphthenes and an increase in the number of cycles also increase the viscosity. For various groups of hydrocarbons, the viscosity increases in the series alkanes - arenes - cyclanes.
To determine the viscosity, special standard instruments are used - viscometers, which differ in the principle of operation.
Kinematic viscosity is determined for relatively low-viscosity light petroleum products and oils using capillary viscometers, the operation of which is based on the fluidity of a liquid through a capillary according to GOST 33-2000 and GOST 1929-87 (viscometer type VPZh, Pinkevich, etc.).
For viscous petroleum products, the relative viscosity is measured in viscometers such as VU, Engler, etc. The outflow of liquid in these viscometers occurs through a calibrated hole in accordance with GOST 6258-85.
There is an empirical relationship between the values of conventional °VU and kinematic viscosity:
The viscosity of the most viscous, structured petroleum products is determined on a rotational viscometer according to GOST 1929-87. The method is based on measuring the force required to rotate the inner cylinder relative to the outer one when filling the space between them with the test liquid at a temperature t.
In addition to standard methods for determining viscosity, sometimes non-standard methods are used in research work, based on measuring viscosity by the time the calibration ball falls between the marks or by the decay time of the vibrations of a solid body in the test liquid (Geppler, Gurvich viscometers, etc.).
In all standard methods described, the viscosity is determined at a strictly constant temperature, since the viscosity changes significantly with its change.
Viscosity versus temperature
The dependence of the viscosity of petroleum products on temperature is a very important characteristic both in oil refining technology (pumping, heat exchange, settling, etc.) and in the use of commercial petroleum products (draining, pumping, filtering, lubrication of rubbing surfaces, etc.).
As the temperature decreases, their viscosity increases. The figure shows viscosity versus temperature curves for various lubricating oils.
Common to all oil samples is the presence of temperature regions in which a sharp increase in viscosity occurs.
There are many different formulas for calculating viscosity as a function of temperature, but the most commonly used is Walter's empirical formula:
Taking the logarithm of this expression twice, we get:
According to this equation, E. G. Semenido compiled a nomogram on the abscissa axis of which, for ease of use, temperature is plotted, and viscosity is plotted on the ordinate axis.
Using a nomogram, you can find the viscosity of an oil product at any given temperature if its viscosity at two other temperatures is known. In this case, the value of the known viscosities is connected by a straight line and continues until it intersects with the temperature line. The point of intersection with it corresponds to the desired viscosity. The nomogram is suitable for determining the viscosity of all types of liquid petroleum products.
For petroleum lubricating oils, it is very important during operation that the viscosity be as little dependent on temperature as possible, since this ensures good lubricating properties of the oil over a wide temperature range, i.e., in accordance with the Walther formula, this means that for lubricating oils, the lower the coefficient B, the higher the quality of the oil. This property of oils is called viscosity index, which is a function of the chemical composition of the oil. For various hydrocarbons, the viscosity varies with temperature in different ways. The steepest dependence (large value of B) for aromatic hydrocarbons, and the smallest - for alkanes. Naphthenic hydrocarbons are close to alkanes in this respect.
There are various methods for determining the viscosity index (VI).
In Russia, IV is determined by two values of kinematic viscosity at 50 and 100°C (or at 40 and 100°C - according to a special table of the State Committee for Standards).
When certifying oils, IV is calculated according to GOST 25371-97, which provides for the determination of this value by viscosity at 40 and 100°C. According to this method, according to GOST (for oils with VI less than 100), the viscosity index is determined by the formula:
For all oils with v 100 ν, v 1 and v 3) is determined according to the GOST 25371-97 table based on v 40 and v 100 this oil. If the oil is more viscous ( v 100> 70 mm 2 /s), then the quantities included in the formula are determined by special formulas given in the standard.
It is much easier to determine the viscosity index from nomograms.
An even more convenient nomogram for finding the viscosity index was developed by G. V. Vinogradov. The definition of VI is reduced to the connection of known viscosity values at two temperatures with straight lines. The point of intersection of these lines corresponds to the desired viscosity index.
The viscosity index is a generally accepted value that is included in oil standards in all countries of the world. The disadvantage of the viscosity index is that it characterizes the behavior of the oil only in the temperature range from 37.8 to 98.8°C.
Many researchers have noticed that the density and viscosity of lubricating oils to some extent reflect their hydrocarbon composition. A corresponding indicator was proposed that links the density and viscosity of oils and is called the viscosity-mass constant (VMC). The viscosity-mass constant can be calculated by the formula of Yu. A. Pinkevich:
Depending on the chemical composition of the VMK oil, it can be from 0.75 to 0.90, and the higher the VMK oil, the lower its viscosity index.
At low temperatures, lubricating oils acquire a structure that is characterized by yield strength, plasticity, thixotropy or viscosity anomaly, which are characteristic of dispersed systems. The results of determining the viscosity of such oils depend on their preliminary mechanical mixing, as well as on the flow rate, or on both factors at the same time. Structured oils, like other structured petroleum systems, do not follow the Newtonian fluid flow law, according to which the change in viscosity should depend only on temperature.
An oil with an unbroken structure has a significantly higher viscosity than after its destruction. If the viscosity of such an oil is reduced by destroying the structure, then in a calm state this structure will be restored and the viscosity will return to its original value. The ability of a system to spontaneously restore its structure is called thixotropy. With an increase in the flow velocity, more precisely, the velocity gradient (curve section 1), the structure is destroyed, and therefore the viscosity of the substance decreases and reaches a certain minimum. This minimum viscosity remains at the same level even with a subsequent increase in the velocity gradient (section 2) until a turbulent flow appears, after which the viscosity increases again (section 3).
Viscosity versus pressure
The viscosity of liquids, including petroleum products, depends on external pressure. Changing the viscosity of oils with increasing pressure is of great practical importance, since high pressures can occur in some friction units.
The dependence of viscosity on pressure for some oils is illustrated by curves, the viscosity of oils with increasing pressure changes along a parabola. Under pressure R it can be expressed by the formula:
In petroleum oils, the viscosity of paraffinic hydrocarbons changes the least with increasing pressure, and somewhat more naphthenic and aromatic. The viscosity of high-viscosity oil products increases with increasing pressure more than the viscosity of low-viscosity ones. The higher the temperature, the less the viscosity changes with increasing pressure.
At pressures of the order of 500 - 1000 MPa, the viscosity of oils increases so much that they lose their liquid properties and turn into a plastic mass.
To determine the viscosity of petroleum products at high pressure, D.E. Mapston proposed the formula:
Based on this equation, D.E. Mapston developed a nomogram, using which known quantities, for example ν 0 and R, are connected by a straight line and the reading is obtained on the third scale.
Viscosity of mixtures
When compounding oils, it is often necessary to determine the viscosity of the mixtures. As experiments have shown, the additivity of properties is manifested only in mixtures of two components that are very similar in viscosity. With a large difference in the viscosities of the mixed oil products, as a rule, the viscosity is less than that calculated according to the mixing rule. Approximately, the viscosity of a mixture of oils can be calculated if we replace the viscosities of the components with their reciprocal - mobility (fluidity) ψ cm:
Various nomograms can also be used to determine the viscosity of mixtures. The ASTM nomogram and Molin-Gurvich viscosigram have found the greatest application. The ASTM nomogram is based on the Walther formula. The Molin-Gurevich nomogram was compiled on the basis of the experimentally found viscosities of a mixture of oils A and B, of which A has a viscosity of °VU 20 = 1.5, and B has a viscosity of °VU 20 = 60. Both oils were mixed in different ratios from 0 to 100% (vol.), and the viscosity of the mixtures was established experimentally. The nomogram shows the values of viscosity in units. units and in mm 2 / s.
Viscosity of gases and oil vapors
The viscosity of hydrocarbon gases and oil vapors is subject to other laws than for liquids. As the temperature rises, the viscosity of gases increases. This pattern is satisfactorily described by the Sutherland formula:
Length and Distance Converter Mass Converter Bulk Food and Food Volume Converter Area Converter Volume and Recipe Units Converter Temperature Converter Pressure, Stress, Young's Modulus Converter Energy and Work Converter Power Converter Force Converter Time Converter Linear Velocity Converter Flat Angle Converter thermal efficiency and fuel efficiency Converter of numbers in different number systems Converter of units of measurement of quantity of information Currency rates Dimensions of women's clothing and shoes Dimensions of men's clothing and shoes Angular velocity and rotational frequency converter Acceleration converter Angular acceleration converter Density converter Specific volume converter Moment of inertia converter Moment of force converter Torque converter Specific calorific value converter (by mass) Energy density and specific calorific value converter (by volume) Temperature difference converter Coefficient converter Thermal Expansion Coefficient Thermal Resistance Converter Thermal Conductivity Converter Specific Heat Capacity Converter Energy Exposure and Radiant Power Converter Heat Flux Density Converter Heat Transfer Coefficient Converter Volume Flow Converter Mass Flow Converter Molar Flow Converter Mass Flux Density Converter Molar Concentration Converter Mass Concentration in Solution Converter Dynamic ( Kinematic Viscosity Converter Surface Tension Converter Vapor Transmission Converter Vapor Transmission and Vapor Transfer Rate Converter Sound Level Converter Microphone Sensitivity Converter Sound Pressure Level (SPL) Converter Sound Pressure Level Converter with Selectable Reference Pressure Brightness Converter Luminous Intensity Converter Illuminance Converter Computer Resolution Converter graph Frequency and Wavelength Converter Power to Diopter x and Focal Length Diopter Power and Lens Magnification (×) Electric Charge Converter Linear Charge Density Converter Surface Charge Density Converter Bulk Charge Density Converter Electric Current Converter Linear Current Density Converter Surface Current Density Converter Electric Field Strength Converter Electrostatic Potential and Voltage Converter Converter Electrical Resistance Electrical Resistivity Converter Electrical Conductivity Converter Electrical Conductivity Converter Capacitance Inductance Converter US Wire Gauge Converter Levels in dBm (dBm or dBmW), dBV (dBV), watts, etc. units Magnetomotive force converter Magnetic field strength converter Magnetic flux converter Magnetic induction converter Radiation. Ionizing Radiation Absorbed Dose Rate Converter Radioactivity. Radioactive Decay Converter Radiation. Exposure Dose Converter Radiation. Absorbed Dose Converter Decimal Prefix Converter Data Transfer Typography and Image Processing Unit Converter Timber Volume Unit Converter Calculation of Molar Mass Periodic Table of Chemical Elements by D. I. Mendeleev
1 meter per second [m/s] = 3600 meter per hour [m/h]
Initial value
Converted value
meter per second meter per hour meter per minute kilometer per hour kilometer per minute kilometers per second centimeter per hour centimeter per minute centimeter per second millimeter per hour millimeter per minute millimeter per second foot per hour foot per minute foot per second yard per hour yard per minute yard per second mile per hour mile per minute mile per second knot knot (Brit.) speed of light in vacuum first space velocity second space velocity third space velocity earth rotation speed of sound in fresh water speed of sound in sea water (20°C, depth 10 meters) Mach number (20°C, 1 atm) Mach number (SI standard)
More about speed
General information
Speed is a measure of the distance traveled in a given time. Velocity can be a scalar quantity or a vector value - the direction of motion is taken into account. The speed of movement in a straight line is called linear, and in a circle - angular.
Speed measurement
average speed v find by dividing the total distance traveled ∆ x for the total time ∆ t: v = ∆x/∆t.
In the SI system, speed is measured in meters per second. Also commonly used are kilometers per hour in the metric system and miles per hour in the US and UK. When, in addition to the magnitude, the direction is also indicated, for example, 10 meters per second to the north, then we are talking about vector speed.
The speed of bodies moving with acceleration can be found using the formulas:
- a, with initial speed u during the period ∆ t, has a final speed v = u + a×∆ t.
- A body moving with constant acceleration a, with initial speed u and final speed v, has an average speed ∆ v = (u + v)/2.
Average speeds
The speed of light and sound
According to the theory of relativity, the speed of light in a vacuum is the highest speed at which energy and information can travel. It is denoted by the constant c and equal to c= 299,792,458 meters per second. Matter cannot move at the speed of light because it would require an infinite amount of energy, which is impossible.
The speed of sound is usually measured in an elastic medium and is 343.2 meters per second in dry air at 20°C. The speed of sound is lowest in gases and highest in solids. It depends on the density, elasticity, and shear modulus of the substance (which indicates the degree of deformation of the substance under shear loading). Mach number M is the ratio of the speed of a body in a liquid or gas medium to the speed of sound in this medium. It can be calculated using the formula:
M = v/a,
where a is the speed of sound in the medium, and v is the speed of the body. The Mach number is commonly used in determining speeds close to the speed of sound, such as aircraft speeds. This value is not constant; it depends on the state of the medium, which, in turn, depends on pressure and temperature. Supersonic speed - speed exceeding 1 Mach.
Vehicle speed
Below are some vehicle speeds.
- Passenger aircraft with turbofan engines: the cruising speed of passenger aircraft is from 244 to 257 meters per second, which corresponds to 878–926 kilometers per hour or M = 0.83–0.87.
- High-speed trains (like the Shinkansen in Japan): These trains reach top speeds of 36 to 122 meters per second, i.e. 130 to 440 kilometers per hour.
animal speed
The maximum speeds of some animals are approximately equal:
human speed
- Humans walk at about 1.4 meters per second, or 5 kilometers per hour, and run at up to about 8.3 meters per second, or 30 kilometers per hour.
Examples of different speeds
four dimensional speed
In classical mechanics, the vector velocity is measured in three-dimensional space. According to the special theory of relativity, space is four-dimensional, and the fourth dimension, space-time, is also taken into account in the measurement of speed. This speed is called four-dimensional speed. Its direction may change, but the magnitude is constant and equal to c, which is the speed of light. Four-dimensional speed is defined as
U = ∂x/∂τ,
where x represents the world line - a curve in space-time along which the body moves, and τ - "proper time", equal to the interval along the world line.
group speed
Group velocity is the velocity of wave propagation, which describes the propagation velocity of a group of waves and determines the velocity of wave energy transfer. It can be calculated as ∂ ω /∂k, where k is the wave number, and ω - angular frequency. K measured in radians / meter, and the scalar frequency of wave oscillations ω - in radians per second.
Hypersonic speed
Hypersonic speed is a speed exceeding 3000 meters per second, that is, many times higher than the speed of sound. Solid bodies moving at such a speed acquire the properties of liquids, because due to inertia, the loads in this state are stronger than the forces that hold the molecules of matter together during a collision with other bodies. At ultra-high hypersonic speeds, two colliding solid bodies turn into gas. In space, bodies move at precisely this speed, and engineers designing spacecraft, orbital stations, and spacesuits must take into account the possibility of a station or astronaut colliding with space debris and other objects when working in outer space. In such a collision, the skin of the spacecraft and the suit suffer. Equipment designers are conducting hypersonic collision experiments in special laboratories to determine how strong impact suits can withstand, as well as skins and other parts of the spacecraft, such as fuel tanks and solar panels, testing them for strength. To do this, spacesuits and skin are subjected to impacts by various objects from a special installation with supersonic speeds exceeding 7500 meters per second.
Since 1963, in the USSR (GOST 9867-61 "International System of Units"), in order to unify units of measurement in all fields of science and technology, the international (international) system of units (SI, SI) has been recommended for practical use - this is a system of units for measuring physical quantities , adopted by the XI General Conference on Weights and Measures in 1960. It is based on 6 basic units (length, mass, time, electric current, thermodynamic temperature and light intensity), as well as 2 additional units (flat angle, solid angle) ; all other units given in the table are their derivatives. The adoption of a single international system of units for all countries is intended to eliminate the difficulties associated with translating the numerical values of physical quantities, as well as various constants from any one currently operating system (CGS, MKGSS, ISS A, etc.), into another.
| Value name | Units; SI values | Notation | |
|---|---|---|---|
| Russian | international | ||
| I. Length, mass, volume, pressure, temperature | |||
| Meter - a measure of length, numerically equal to the length of the international standard of the meter; 1 m=100 cm (1 10 2 cm)=1000 mm (1 10 3 mm) |
m | m | |
| Centimeter \u003d 0.01 m (1 10 -2 m) \u003d 10 mm | cm | cm | |
| Millimeter \u003d 0.001 m (1 10 -3 m) \u003d 0.1 cm \u003d 1000 microns (1 10 3 microns) | mm | mm | |
| Micron (micrometer) = 0.001 mm (1 10 -3 mm) = 0.0001 cm (1 10 -4 cm) = 10,000 |
mk | μ | |
| Angstrom = one ten billionth of a meter (1 10 -10 m) or one hundred millionth of a centimeter (1 10 -8 cm) | Å | Å | |
| Weight | Kilogram - the basic unit of mass in the metric system of measures and the SI system, numerically equal to the mass of the international standard of the kilogram; 1 kg=1000 g |
kg | kg |
| Gram \u003d 0.001 kg (1 10 -3 kg) |
G | g | |
| Ton = 1000 kg (1 10 3 kg) | t | t | |
| Centner \u003d 100 kg (1 10 2 kg) |
c | ||
| Carat - non-systemic unit of mass, numerically equal to 0.2 g | ct | ||
| Gamma=one millionth of a gram (1 10 -6 g) | γ | ||
| Volume | Liter \u003d 1.000028 dm 3 \u003d 1.000028 10 -3 m 3 | l | l |
| Pressure | Physical, or normal, atmosphere - pressure balanced by a mercury column 760 mm high at a temperature of 0 ° = 1.033 at = = 1.01 10 -5 n / m 2 = 1.01325 bar = 760 torr = 1.033 kgf / cm 2 |
atm | atm |
| Technical atmosphere - pressure equal to 1 kgf / cmg \u003d 9.81 10 4 n / m 2 \u003d 0.980655 bar \u003d 0.980655 10 6 dynes / cm 2 \u003d 0.968 atm \u003d 735 torr | at | at | |
| Millimeter of mercury column \u003d 133.32 n / m 2 | mmHg Art. | mm Hg | |
| Tor - the name of an off-system unit of pressure measurement, equal to 1 mm Hg. Art.; given in honor of the Italian scientist E. Torricelli | torus | ||
| Bar - unit of atmospheric pressure \u003d 1 10 5 n / m 2 \u003d 1 10 6 dynes / cm 2 | bar | bar | |
| Pressure (sound) | Bar-unit of sound pressure (in acoustics): bar - 1 dyne / cm 2; at present, a unit with a value of 1 n / m 2 \u003d 10 dynes / cm 2 is recommended as a unit of sound pressure |
bar | bar |
| The decibel is a logarithmic unit of measurement of the level of excess sound pressure, equal to 1/10 of the unit of measurement of excess pressure - white | dB | db | |
| Temperature | Degree Celsius; temperature in °K (Kelvin scale), equal to temperature in °C (Celsius scale) + 273.15 °C | °С | °С |
| II. Force, power, energy, work, amount of heat, viscosity | |||
| Strength | Dyna - a unit of force in the CGS system (cm-g-sec.), At which an acceleration equal to 1 cm / sec 2 is reported to a body with a mass of 1 g; 1 din - 1 10 -5 n | din | dyn |
| Kilogram-force is a force imparting to a body with a mass of 1 kg an acceleration equal to 9.81 m / s 2; 1kg \u003d 9.81 n \u003d 9.81 10 5 din | kg, kgf | ||
| Power | Horsepower=735.5W | l. With. | HP |
| Energy | Electron-volt - the energy that an electron acquires when moving in an electric field in vacuum between points with a potential difference of 1 V; 1 ev \u003d 1.6 10 -19 j. Multiple units are allowed: kiloelectron-volt (Kv) = 10 3 eV and megaelectron-volt (MeV) = 10 6 eV. In modern particles, the energy is measured in Bev - billions (billions) eV; 1 Bzv=10 9 ev |
ev | eV |
| Erg=1 10 -7 J; erg is also used as a unit of work, numerically equal to the work done by a force of 1 dyne in a path of 1 cm | erg | erg | |
| Work | Kilogram-force-meter (kilogrammeter) - a unit of work numerically equal to the work done by a constant force of 1 kg when the point of application of this force moves a distance of 1 m in its direction; 1kGm = 9.81 J (at the same time, kGm is a measure of energy) | kgm, kgf m | kgm |
| Quantity of heat | Calorie - an off-system unit for measuring the amount of heat equal to the amount of heat required to heat 1 g of water from 19.5 ° C to 20.5 ° C. 1 cal = 4.187 j; common multiple unit kilocalorie (kcal, kcal), equal to 1000 cal | feces | cal |
| Viscosity (dynamic) | Poise is a unit of viscosity in the CGS system of units; the viscosity at which a 1 dyne viscous force acts in a layered flow with a velocity gradient of 1 sec -1 per 1 cm 2 of the layer surface; 1 pz \u003d 0.1 n s / m 2 | pz | P |
| Viscosity (kinematic) | Stokes is the unit of kinematic viscosity in the CGS system; equal to the viscosity of a liquid having a density of 1 g / cm 3, resisting a force of 1 dyne to the mutual movement of two layers of liquid with an area of \u200b\u200b1 cm 2 located at a distance of 1 cm from each other and moving relative to each other at a speed of 1 cm per second | st | St |
| III. Magnetic flux, magnetic induction, magnetic field strength, inductance, capacitance | |||
| magnetic flux | Maxwell - a unit of measurement of magnetic flux in the cgs system; 1 μs is equal to the magnetic flux passing through the area of 1 cm 2 located perpendicular to the lines of induction of the magnetic field, with an induction equal to 1 gauss; 1 μs = 10 -8 wb (Weber) - units of magnetic current in the SI system | ms | Mx |
| Magnetic induction | Gauss is a unit of measure in the cgs system; 1 gauss is the induction of such a field in which a rectilinear conductor 1 cm long, located perpendicular to the field vector, experiences a force of 1 dyne if a current of 3 × 10 10 CGS units flows through this conductor; 1 gs \u003d 1 10 -4 t (tesla) | gs | Gs |
| Magnetic field strength | Oersted - unit of magnetic field strength in the CGS system; for one oersted (1 e) the intensity at such a point of the field is taken, in which a force of 1 dyne (dyne) acts on 1 electromagnetic unit of the amount of magnetism; 1 e \u003d 1 / 4π 10 3 a / m |
uh | Oe |
| Inductance | Centimeter - a unit of inductance in the CGS system; 1 cm = 1 10 -9 gn (henry) | cm | cm |
| Electrical capacitance | Centimeter - unit of capacitance in the CGS system = 1 10 -12 f (farads) | cm | cm |
| IV. Light intensity, luminous flux, brightness, illumination | |||
| The power of light | A candle is a unit of luminous intensity, the value of which is taken so that the brightness of a full emitter at the solidification temperature of platinum is 60 sv per 1 cm 2 | St. | cd |
| Light flow | Lumen - a unit of luminous flux; 1 lumen (lm) is radiated within a solid angle of 1 stere by a point source of light that has a luminous intensity of 1 St in all directions. | lm | lm |
| Lumen-second - corresponds to the light energy generated by a luminous flux of 1 lm, emitted or perceived in 1 second | lm s | lm sec | |
| Lumen hour equals 3600 lumen seconds | lm h | lm h | |
| Brightness | Stilb is a unit of brightness in the CGS system; corresponds to the brightness of a flat surface, 1 cm 2 of which gives in the direction perpendicular to this surface, a luminous intensity equal to 1 ce; 1 sb \u003d 1 10 4 nt (nit) (unit of brightness in the SI system) | Sat | sb |
| Lambert is an off-system unit of brightness, derived from the stilb; 1 lambert = 1/π st = 3193 nt | |||
| Apostille = 1 / π St / m 2 | |||
| illumination | Fot - unit of illumination in the SGSL system (cm-g-sec-lm); 1 ph corresponds to the surface illumination of 1 cm 2 with a uniformly distributed luminous flux of 1 lm; 1 f \u003d 1 10 4 lux (lux) | f | ph |
| V. Radiation intensity and doses | |||
| Intensity | Curie is the basic unit for measuring the intensity of radioactive radiation, curie corresponding to 3.7·10 10 decays in 1 sec. any radioactive isotope |
curie | C or Cu |
| millicurie \u003d 10 -3 curie, or 3.7 10 7 acts of radioactive decay in 1 sec. | mcurie | mc or mCu | |
| microcurie = 10 -6 curie | microcurie | μC or μCu | |
| Dose | X-ray - the amount (dose) of X-ray or γ-rays, which in 0.001293 g of air (i.e., in 1 cm 3 of dry air at t ° 0 ° and 760 mm Hg) causes the formation of ions that carry one electrostatic a unit of the amount of electricity of each sign; 1 p causes the formation of 2.08 10 9 pairs of ions in 1 cm 3 of air | R | r |
| milliroentgen \u003d 10 -3 p | mr | mr | |
| microroentgen = 10 -6 p | microdistrict | µr | |
| Rad - the unit of the absorbed dose of any ionizing radiation is equal to rad 100 erg per 1 g of the irradiated medium; when air is ionized by x-rays or γ-rays, 1 p is equal to 0.88 rad, and when tissues are ionized, practically 1 p is equal to 1 rad | glad | rad | |
| Rem (X-ray biological equivalent) - the amount (dose) of any type of ionizing radiation that causes the same biological effect as 1 p (or 1 rad) of hard X-rays. The unequal biological effect with equal ionization by different types of radiation led to the need to introduce another concept: the relative biological effectiveness of radiation -RBE; the relationship between doses (D) and the dimensionless coefficient (RBE) is expressed as Drem =D rad RBE, where RBE=1 for x-rays, γ-rays and β-rays and RBE=10 for protons up to 10 MeV, fast neutrons and α - natural particles (on the recommendation of the International Congress of Radiologists in Copenhagen, 1953) | reb, reb | rem | |
Note. Multiple and submultiple units of measurement, with the exception of units of time and angle, are formed by multiplying them by the corresponding power of 10, and their names are attached to the names of units of measurement. It is not allowed to use two prefixes to the name of the unit. For example, you cannot write millimicrowatts (mmkw) or micromicrofarads (mmf), but you must write nanowatts (nw) or picofarads (pf). You should not use prefixes to the names of such units that indicate a multiple or submultiple unit of measurement (for example, micron). Multiple units of time may be used to express the duration of processes and designate calendar dates of events.
The most important units of the International System of Units (SI)
Basic units
(length, mass, temperature, time, electric current, light intensity)
| Value name | Notation | ||
|---|---|---|---|
| Russian | international | ||
| Length | A meter is a length equal to 1650763.73 wavelengths of radiation in vacuum, corresponding to the transition between levels 2p 10 and 5d 5 krypton 86 * |
m | m |
| Weight | Kilogram - mass corresponding to the mass of the international standard of the kilogram | kg | kg |
| Time | Second - 1/31556925.9747 part of a tropical year (1900) ** | sec | S, s |
| The strength of the electric current | Ampere - the strength of an unchanging current, which, passing through two parallel rectilinear conductors of infinite length and negligible circular cross section, located at a distance of 1 m from one another in a vacuum, would cause a force between these conductors equal to 2 10 -7 n for each meter length | a | A |
| The power of light | Candle - a unit of luminous intensity, the value of which is taken so that the brightness of a full (absolutely black) emitter at the solidification temperature of platinum is 60 ce per 1 cm 2 *** | St. | cd |
| Temperature (thermodynamic) | Degree Kelvin (Kelvin scale) - a unit of temperature measurement according to the thermodynamic temperature scale, in which the temperature of the triple point of water **** is set to 273.16 ° K | °K | °K |
** That is, a second is equal to the specified part of the time interval between two successive passages of the Earth in orbit around the Sun of the point corresponding to the vernal equinox. This gives greater accuracy in determining the second than defining it as part of a day, since the length of the day varies.
*** That is, the luminous intensity of a certain reference source emitting light at the melting temperature of platinum is taken as a unit. The old International Candlestick Standard is 1.005 of the new Candlestick Standard. Thus, within the limits of usual practical accuracy, their values can be considered as coinciding.
**** Triple point - melting temperature of ice in the presence of saturated water vapor above it.
Complementary and derived units
| Value name | Units; their definition | Notation | |
|---|---|---|---|
| Russian | international | ||
| I. Flat angle, solid angle, force, work, energy, amount of heat, power | |||
| flat corner | Radian - the angle between two radii of a circle, cutting an arc on a circle rad, the length of which is equal to the radius | glad | rad |
| Solid angle | Steradian - a solid angle whose vertex is located in the center of the sphere ster and which cuts out on the surface of the sphere an area equal to the area of a square with a side equal to the radius of the sphere | erased | sr |
| Strength | Newton force, under the influence of which a body with a mass of 1 kg acquires an acceleration equal to 1 m / s 2 | n | N |
| Work, energy, amount of heat | Joule - the work done by a constant force of 1 n acting on the body on a path of 1 m traveled by the body in the direction of the force | j | J |
| Power | Watt - the power at which for 1 sec. work done in 1 j | Tue | W |
| II. Quantity of electricity, electrical voltage, electrical resistance, electrical capacitance | |||
| Quantity of electricity, electric charge | Pendant - the amount of electricity flowing through the cross section of the conductor for 1 second. at a direct current of 1 a | to | C |
| Electrical voltage, electrical potential difference, electromotive force (EMF) | Volt - the voltage in the section of the electrical circuit, when passing through which the amount of electricity in 1 k, work is done in 1 j | in | V |
| Electrical resistance | Ohm - the resistance of the conductor, through which, at a constant voltage at the ends of 1 V, a direct current of 1 A passes | ohm | Ω |
| Electrical capacitance | Farad is the capacitance of a capacitor, the voltage between the plates of which changes by 1 V when it is charged with an amount of electricity of 1 kV. | f | F |
| III. Magnetic induction, magnetic flux, inductance, frequency | |||
| Magnetic induction | Tesla is the induction of a homogeneous magnetic field, which acts on a section of a rectilinear conductor 1 m long, placed perpendicular to the direction of the field, with a force of 1 n when a direct current of 1 a passes through the conductor | tl | T |
| Flux of magnetic induction | Weber - magnetic flux created by a uniform field with a magnetic induction of 1 t through an area of 1 m 2 perpendicular to the direction of the magnetic induction vector | wb | wb |
| Inductance | Henry is the inductance of a conductor (coil) in which an EMF of 1 V is induced when the current in it changes by 1 A in 1 sec. | Mr | H |
| Frequency | Hertz - the frequency of a periodic process, in which for 1 sec. one oscillation occurs (cycle, period) | Hz | Hz |
| IV. Luminous flux, light energy, brightness, illumination | |||
| Light flow | Lumen - the luminous flux that gives inside a solid angle of 1 ster a point source of light of 1 s, radiating equally in all directions | lm | lm |
| light energy | Lumen second | lm s | lm s |
| Brightness | Nit - the brightness of a luminous plane, each square meter of which gives in a direction perpendicular to the plane, a luminous intensity of 1 sv | nt | nt |
| illumination | Lux - illumination created by a luminous flux of 1 lm with its uniform distribution over an area of 1 m 2 | OK | lx |
| Light quantity | lux second | lx sec | lx s |
Loading...