DEFINITION

carbon steels- these are alloys of iron with carbon, and the content of the latter does not exceed 2.14%.

However, in carbon steel industrial production there are always impurities of many elements. The presence of some impurities is due to the peculiarities of steel production: for example, during deoxidation, small amounts of manganese or silicon are introduced into steel, which partially pass into the slag in the form of oxides, and partially remain in the steel. The presence of other impurities is due to the fact that they are contained in the original ore and in small quantities pass into cast iron, and then into steel. It is difficult to get rid of them completely. As a result, for example, carbon steels usually contain 0.05 - 0.1% phosphorus and sulfur.

The mechanical properties of slowly cooled carbon steel are highly dependent on its carbon content. Slowly cooled steel is composed of ferrite and cementite, the amount of cementite being proportional to the carbon content. The hardness of cementite is much higher than the hardness of ferrite. Therefore, with an increase in the carbon content in steel, its hardness increases. In addition, cementite particles impede the movement of dislocations in the main phase - in ferrite. For this reason, increasing the amount of carbon reduces the ductility of the steel.

Carbon steel has a wide range of applications. Depending on the purpose, steel with a low or higher carbon content is used, without heat treatment(in a "raw" form - after rolling) or with hardening and tempering.

Elements specially introduced into steel in certain concentrations to change its properties are called alloying elements, and steel containing such elements is called alloy steel. The most important alloying elements include chromium, nickel, manganese, silicon, vanadium, molybdenum.

Various alloying elements change the structure and properties of steel in different ways. Thus, some elements form solid solutions in g-iron, which are stable over a wide temperature range. For example, solid solutions of manganese or nickel in g-iron with a significant content of these elements are stable from room temperature to the melting point. Alloys of iron with similar metals are called austenitic steels or austenitic alloys.

The influence of alloying elements on the properties of steel is also due to the fact that some of them form carbides with carbon, which can be simple, for example Mn 3 C, Cr 7 C 3, as well as complex (double), for example (Fe, Cr) 3 C. The presence carbides, especially in the form of dispersed inclusions in the structure of steel, in some cases has a strong effect on its mechanical and physicochemical properties.

Purpose and density of steel

According to their purpose, steels are divided into structural, tool and steels with special properties. Structural steels are used for the manufacture of machine parts, structures and structures. Both carbon and alloy steels can be used as structural steels. Structural steels have high strength and ductility. At the same time, they must lend themselves well to pressure treatment, cutting, and good welding. The main alloying components of structural steels are chromium (about 1%), nickel (1-4%) and manganese (1-1.5%).

DEFINITION

Tool steels- These are carbon and alloy steels with high hardness, strength and wear resistance.

They are used for the manufacture of cutting and measuring tools, stamps. The necessary hardness is provided by the carbon contained in these steels (in an amount from 0.8 to 1.3%). The main alloying element of tool steels is chromium; sometimes they also introduce tungsten and vanadium. A special group of tool steels is high-speed steel, which retains cutting properties at high cutting speeds, when the temperature of the working part of the cutter rises to 600-700 o C. The main alloying elements of this steel are chromium and tungsten.

The group of steels with special properties includes stainless, heat-resistant, heat-resistant, magnetic and some other steels. Stainless steels are resistant to corrosion in the atmosphere, moisture and acid solutions, heat-resistant - in corrosive environments at high temperatures. Heat-resistant steels retain high mechanical properties when heated to significant temperatures, which is important in the manufacture of blades gas turbines, parts of jet engines and rocket launchers. The most important alloying elements of heat-resistant steels are chromium (15-20%), nickel (8-15%), tungsten.

Examples of problem solving

EXAMPLE 1

EXAMPLE 2

Exercise	The density of a simple substance of fluorine gas in air is 1.31. Calculate the molar mass of fluorine and its formula.
Solution	The ratio of the mass of a given gas to the mass of another gas taken in the same volume, at the same temperature and the same pressure, is called the relative density of the first gas over the second. This value shows how many times the first gas is heavier or lighter than the second gas. The molar mass of a gas is equal to its density with respect to another gas, multiplied by the molar mass of the second gas: The relative molecular weight of air is taken equal to 29 (taking into account the content of nitrogen, oxygen and other gases in the air). It should be noted that the concept of "relative molecular weight of air" is used conditionally, since air is a mixture of gases. Then, the molar mass of fluorine gas will be equal to: M gas \u003d D air × M (air) \u003d 1.31 × 29 \u003d 37.99 g / mol. The relative atomic mass of fluorine is 18.9984 amu. Then, the composition of the fluorine molecule includes M gas /A r (F) of fluorine atoms: M gas / Ar (F) = 37.99 / 18.9984 = 2. So the formula of the fluorine molecule is F 2.
Answer	The molar mass of fluorine is 37.99 g/mol, and the formula of the fluorine molecule is F 2 .

Steel- deformable (ductile) alloy of iron with carbon (up to 2%) and other elements. It is the most important material that is used in most industries. There are a large number of steel grades that differ in structure, chemical composition, mechanical and physical properties.

The main characteristics of steel:

• density
• modulus of elasticity and shear modulus
• linear expansion coefficient
• other

Based on their chemical composition, steels are divided into carbonaceous and doped. Carbon steel, along with iron and carbon, contains manganese (0.1-1.0%), silicon (up to 0.4%).

Steel also contains harmful impurities (phosphorus, sulfur, gases - unbound nitrogen and oxygen). Phosphorus at low temperatures gives it brittleness (cold brittleness), and when heated reduces plasticity. Sulfur leads to the formation of small cracks at high temperatures (red brittleness).

To give steel any special properties (corrosion resistance, electrical, mechanical, magnetic, etc.), alloying elements are introduced into it. Usually these are metals: aluminum, nickel, chromium, molybdenum, etc. Such steels are called alloyed.

Steel properties can be changed by applying various kinds processing: thermal (hardening, annealing), chemical-thermal (cementing, nitriding), thermo-mechanical (rolling, forging). When processing to receive necessary structure use the property of polymorphism inherent in steel in the same way as their base - iron. Polymorphism - the ability of a crystal lattice to change its structure when heated and cooled. The interaction of carbon with two modifications (modifications) of iron - α and γ - leads to the formation of solid solutions. Excess carbon, which does not dissolve in α-iron, forms a chemical compound with it - cementite Fe 3 C. When steel is quenched, a metastable phase is formed - martensite - a supersaturated solid solution of carbon in α-iron. In this case, the steel loses its ductility and acquires high hardness. By combining quenching with subsequent heating (tempering), an optimal combination of hardness and ductility can be achieved.

According to their purpose, steels are divided into structural, tool and steels with special properties.

Structural steels are used to make building structures, parts of machines and mechanisms, ship and carriage hulls, steam boilers. Tool steels are used for the manufacture of cutters, dies and other cutting, impact-die and measuring tools. Steels with special properties include electrical, stainless, acid-resistant, etc.

According to the manufacturing method, steel can be open-hearth and oxygen-converter (boiling, calm and semi-quiet). Boiling steel is immediately poured from the ladle into molds, it contains a significant amount of dissolved gases. Quiet steel is steel that has been aged for some time in ladles along with deoxidizers (silicon, manganese, aluminum), which, when combined with dissolved oxygen, turn into oxides and float to the surface of the steel mass. This steel has the best composition and a more homogeneous structure, but more expensive than boiling by 10-15%. Semi-quiet steel occupies an intermediate position between calm and boiling.

In modern metallurgy, steel is smelted mainly from cast iron and steel scrap. The main types of units for its smelting: open-hearth furnace, oxygen converter, electric furnaces. The oxygen-converter method of steel production is considered the most progressive today. At the same time, new, promising methods of its production are being developed: direct reduction of steel from ore, electrolysis, electroslag remelting, etc. When smelting steel, pig iron is loaded into a steel furnace, adding metal waste and iron scrap containing iron oxides, which serve as a source of oxygen. Smelting is carried out at the highest possible temperatures in order to accelerate the melting of solid starting materials. In this case, the iron contained in cast iron is partially oxidized:

2Fe + O 2 \u003d 2FeO + Q

The resulting iron oxide (II) FeO, mixing with the melt, oxidizes silicon, manganese, phosphorus and carbon, which are part of the cast iron:

Si + 2FeO \u003d SiO 2 + 2 Fe + Q

Mn + FeO = MnO + Fe + Q

2P + 5FeO = P 2 O 5 + 5Fe + Q

C + FeO = CO + Fe - Q

To complete the oxidative reactions in the melt, add the so-called deoxidizers - ferromanganese, ferrosilicon, aluminum.

Steel grades

Carbon steel grades

Carbon steel ordinary quality It is divided into three groups depending on the purpose:

• group A - supplied by mechanical properties;
• group B - supplied by chemical composition;
• group B - supplied in terms of mechanical properties and chemical composition.

Depending on the normalized indicators, steels of group A are divided into three categories: A1, A2, A3; steel group B into two categories: B1 and B2; steel group B into six categories: B1, B2, B3, B4, B5, B6. For group A steel, grades St0, St1, St2, St3, St4, St5, St6 are established. For steel group B grades Bst0, Bst1, Bst2, Bst3, Bst4, Bst5, Bst6. Group B steel is produced by open-hearth and converter methods. The grades VST2, VST3, VST4, VST5 are installed for it.

The letters St denote steel, the numbers from 0 to 6 - the conditional number of the steel grade, depending on chemical composition and mechanical properties. With an increase in the number of steel, the tensile strength (σ in) and yield strength (σ t) increase, and the relative elongation decreases (δ 5).

Steel grade St0 is assigned to steel rejected for any reason. This steel is used in non-critical structures.

In critical structures, St3sp steel is used.

The letters B and C indicate the steel group, group A is not indicated in the designation.

If steel refers to boiling, the index "kp" is put, if semi-resistant - "ps", to calm - "sp".

Quality carbon structural steels used for the manufacture of critical welded structures. quality steels according to GOST 1050-74 are marked with two-digit numbers indicating the average carbon content in hundredths of a percent. For example, grades 10, 15, 20, etc. mean that the steel contains an average of 0.10%, 0.15%, 0.2% carbon.

Steel according to GOST 1050-74 is produced in two groups: group I - with a normal manganese content (0.25-0.8%), group II - with a high manganese content (0.7-1.2%). With an increased manganese content, the letter G is additionally introduced into the designation, indicating that the steel has an increased manganese content.

Alloy steel grades

Alloy steels, in addition to the usual impurities, contain elements specially introduced in certain quantities to provide the required properties. These elements are called ligating. Alloyed steels are subdivided depending on the content of alloying elements into low-alloyed (2.5% of alloying elements), medium-alloyed (from 2.5 to 10% and high-alloyed (over 10%).

Alloying additives increase the strength, corrosion resistance of steel, reduce the risk of brittle fracture. Chromium, nickel, copper, nitrogen (in a chemically bound state), vanadium, etc. are used as alloying additives.

Alloy steels are marked with numbers and letters indicating the approximate composition of the steel. The letter shows which alloying element is included in the steel (G - manganese, C - silicon, X - chromium, H - nickel, D - copper, A - nitrogen, F - vanadium), and the numbers behind it - the average content of the element in percent. If the element contains less than 1%, then the numbers behind the letter are not put. The first two digits indicate the average carbon content in hundredths of a percent.

Stainless steel. Properties. Chemical composition

Stainless steel - alloy steel, resistant to corrosion in air, in water, and also in some aggressive environments. The most common are chromium-nickel (18% Cr b 9% Ni) and chromium (13-27% Cr) stainless steel, often with the addition of Mn, Ti and other elements.

The addition of chromium increases the resistance of steel to oxidation and corrosion. Such steel retains its strength at high temperatures. Chromium is also part of wear-resistant steels, which are used to make tools, ball bearings, and springs.

Approximate chemical composition of stainless steel (in %)

Damascus and damask steel.

Damascus steel- originally the same as bulat; later - steel obtained by forge welding of steel strips or wires woven into a bundle with different carbon contents. It got its name from the city of Damascus (Syria), where the production of this steel was developed in the Middle Ages and, partly, in modern times.

Bulat steel (bulat)- cast carbon steel with a peculiar structure and patterned surface, with high hardness and elasticity. Bladed weapons of exceptional durability and sharpness were made from damask steel. Damascus steel is mentioned by Aristotle. The secret of making damask steel, lost in the Middle Ages, was revealed in the 19th century by P.P. Anosov. Based on science, he determined the role of carbon as an element that affects the quality of steel, and also studied the significance of a number of other elements. Having found out the most important conditions for education the best variety carbon steel - damask steel, Anosov developed the technology of its smelting and processing (Anosov P.P. About damask steel. Mining magazine, 1841, No. 2, p. 157-318).

• Density of steel, specific gravity of steel and other characteristics of steel
• steel density - (7,7-7,9)*10 3 kg/ m 3;
• Specific weight of steel - (7,7-7,9) G/ cm 3;
• Specific heat capacity of steel at 20°C- 0.11 cal/deg;
• Melting temperature of steel- 1300-1400°C ;
• Specific heat of steel melting- 49 cal / hail;
• Thermal conductivity of steel- 39 kcal / m * hour * hail;
• Coefficient of linear expansion of steel
  • (at approx. 20°C) :
  • steel 3 (grade 20) - 11.9 (1/deg);
  • stainless steel - 11.0 (1/deg).
• Tensile strength of steel :
  • steel for structures - 38-42 (kg / mm 2);
  • silicon-chromium-manganese steel - 155 (kg / mm 2);
  • machine-made steel (carbon) - 32-80 (kg / mm 2);
  • rail steel - 70-80 (kg / mm 2);
• Density of steel, specific gravity of steel
  • Steel density - (7.7-7.9) * 10 3 kg/ m 3 (approximately 7.8 * 10 3 kg/ m 3);
  • The density of a substance (in our case, steel) is the ratio of the mass of a body to its volume (in other words, the density is equal to the mass per unit volume of a given substance):
  • d=m/V, where m and V are the mass and volume of the body.
  • The unit of density is taken to be the density of such a substance, the unit volume of which has a mass equal to one:
  • in the SI system it is 1 kg/ m 3, in the CGS system - 1 G/ cm 3, in the MKSS system - 1 topics/ m 3. These units are related to each other by the ratio:
  • 1 kg/ m 3 \u003d 0.001 G/ cm 3 \u003d 0.102 topics/ m 3.
• Specific weight of steel - (7,7-7,9) G/ cm 3 (approximately 7.8 G/cm 3);
  • The specific gravity of a substance (in our case, steel) is the ratio of the gravity P of a homogeneous body from a given substance (in our case, steel) to the volume of the body. If we denote the specific gravity by the letter γ, then:
  • γ=P/V .
  • On the other hand, specific gravity can be viewed as the force of gravity per unit volume of a given substance (in our case, steel). Specific gravity and density are related by the same relationship as weight and body mass:
  • γ/d=P/m=g.
  • The unit of specific gravity is taken: in the SI system - 1 n/ m 3, in the CGS system - 1 days/ cm 3, in the MKSS system - 1 kg / m 3. These units are related to each other by the ratio:
  • 1 n/ m 3 \u003d 0.0001 days/ cm 3 \u003d 0.102 kg / m 3.
  • Sometimes an off-system unit of 1 g/cm 3 is used.
  • Since the mass of a substance, expressed in terms of G, is equal to its weight, expressed in G, then the specific gravity of the substance (in our case, steel), expressed in these units, is numerically equal to the density of this substance, expressed in the CGS system.
  • A similar numerical equality exists between the density in the SI system and the specific gravity in the MCSS system.

steel density

Modulus of elasticity of steel and Poisson's ratio

The values ​​​​of allowable stresses of steel (kg / mm 2)

Properties of some electrical steels

Normalized chemical composition carbon steels ordinary quality according to GOST 380-71

steel grade	Content of elements, %
	C	Mn	Si	P	S
				no more
St0	Not more than 0.23	-	-	0,07	0,06
St2ps St2sp	0,09...0,15	0,25...0,50	0,05...0,07 0,12...0,30	0,04	0,05
St3kp St3ps St3sp St3Gps	0,14...0,22	0,30...0,60 0,40...0,65 0,40...0,65 0,80...1,10	no more than 0.07 0,05...0,17 0,12...0,30 no more than 0.15	0,04	0,05
St4kp St4ps St4sp	0,18...0,27	0,40...0,70	no more than 0.07 0,05...0,17 0,12...0,30	0,04	0,05
St5ps St5sp	0,28...0,37	0,50...0,80	0,05...0,17 0,12...0,35	0,04	0,05
St5Gps	0,22...0,30	0,80...1,20	no more than 0.15	0,04	0,05

Normalized indicators of mechanical properties of carbon steels of ordinary quality according to GOST 380-71

steel grade	Tensile strength (temporary resistance) σ in, MPa	Yield strength σ t, MPa			Relative elongation of short samples δ 5, %		180° bend with mandrel diameter d
		sample thickness s, mm
		up to 20	20...40	40...100	up to 20	20...40	40...100	up to 20
St0	310	-	-	-	23	22	20	d=2s
VST2ps VST2sp	340...440	230	220	210	32	31	29	d=0 (without mandrel)
Vst3kp Vst3ps VSt3sp VSt3Gps	370...470 380...490 380...500	240 250 250	230 240 240	220 230 230	27 26 26	26 25 25	24 23 23	d=0.5s
Vst4kp VST4ps VSt4Gsp	410...520 420...540	260 270	250 260	240 250	25 24	24 23	22 21	d=2s
VSt5ps VSt5sp VSt5Gps	500...640 460...600	290 290	280 280	270 270	20 20	19 19	17 17	d=3s

Notes: 1. For sheet and shaped steel with a thickness of s>=20 mm, the value of the yield strength is allowed to be 10 MPa lower than indicated. 2. For s<20 мм диаметр оправки увеличивается на толщину образца.

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1 kilogram per cubic meter [kg/m³] = 1 gram per liter [g/l]

Initial value

Converted value

kilogram per cubic meter kilogram per cubic centimeter gram per cubic meter gram per cubic centimeter gram per cubic millimeter milligram per cubic meter milligram per cubic centimeter milligram per cubic millimeter exagram per liter petagram per liter teragram per liter gigagram per liter megagram per liter kilogram per liter hectogram per liter decagram per liter gram per liter decigram per liter centigram per liter milligram per liter microgram per liter nanogram per liter picogram per liter femtogram per liter attogram per liter pound per cubic inch pound per cubic foot pound per cubic yard pound per gallon (US) ) pound per gallon (UK) ounce per cubic inch ounce per cubic foot ounce per gallon (US) ounce per gallon (UK) grain per gallon (US) grain per gallon (UK) grain per cubic foot short ton per cubic foot yard long ton per cubic yard slug per cubic foot Earth's average density slug per cubic inch slug per cubic yard Plankowska i density

Data transmission and Kotelnikov's theorem

More about density

General information

Density is a property that determines the amount of a substance by mass per unit volume. In the SI system, density is measured in kg / m³, but other units are also used, such as g / cm³, kg / l and others. In everyday life, two equivalent values ​​\u200b\u200bare most often used: g / cm³ and kg / ml.

Factors affecting the density of matter

The density of the same substance depends on temperature and pressure. Generally, the higher the pressure, the tighter the molecules are packed, which increases the density. In most cases, an increase in temperature, on the contrary, increases the distance between molecules and reduces the density. In some cases, this relationship is reversed. The density of ice, for example, is less than that of water, even though ice is colder than water. This can be explained by the molecular structure of ice. Many substances, when moving from a liquid to a solid state of aggregation, change their molecular structure so that the distance between molecules decreases, and the density, respectively, increases. During the formation of ice, the molecules line up in a crystal structure and the distance between them, on the contrary, increases. In this case, the attraction between the molecules also changes, the density decreases, and the volume increases. In winter, you must not forget about this property of ice - if the water in the water pipes freezes, then they can break.

Density of water

If the density of the material from which the object is made is greater than the density of water, then it is completely immersed in water. Materials with a density less than that of water, on the contrary, float to the surface. A good example is ice, which is less dense than water and floats in a glass to the surface of water and other drinks that are mostly water. We often use this property of substances in everyday life. For example, in the construction of ship hulls, materials with a density higher than that of water are used. Since materials with a density higher than that of water sink, air-filled cavities are always created in the ship's hull, since the density of air is much lower than that of water. On the other hand, sometimes it is necessary that the object sink in water - for this, materials with a higher density than water are chosen. For example, in order to sink light bait to a sufficient depth while fishing, anglers tie a sinker made of materials having a high density, such as lead, to the fishing line.

Oil, fat and oil remain on the surface of the water because their density is lower than that of water. Thanks to this property, oil spilled in the ocean is much easier to clean up. If it mixed with water or sank to the seabed, it would cause even more damage to the marine ecosystem. This property is also used in cooking, but not oil, of course, but fat. For example, it is very easy to remove excess fat from soup as it floats to the surface. If the soup is cooled in the refrigerator, the fat solidifies, and it is even easier to remove it from the surface with a spoon, slotted spoon, or even a fork. In the same way, it is removed from jelly and aspic. This reduces the calorie and cholesterol content of the product.

Information about the density of liquids is also used during the preparation of drinks. Layered cocktails are made from liquids of different densities. Typically, lower density liquids are carefully poured onto higher density liquids. You can also use a glass cocktail stick or bar spoon and slowly pour the liquid over them. If you do not rush and do everything carefully, you will get a beautiful multi-layered drink. This method can also be used with jellies or aspic dishes, although if time permits it is easier to cool each layer separately, pouring a new layer only after the bottom layer has hardened.

In some cases, a lower fat density, on the contrary, interferes. Products with a high fat content often do not mix well with water and form a separate layer, thus impairing not only the appearance, but also the taste of the product. For example, in cold desserts and fruit smoothies, fatty dairy products are sometimes separated from non-fat dairy products such as water, ice, and fruit.

Salt water density

The density of water depends on the content of impurities in it. In nature and in everyday life, pure H 2 O water without impurities is rarely found - most often it contains salts. A good example is sea water. Its density is higher than that of fresh water, so fresh water usually "floats" on the surface of salt water. Of course, it is difficult to see this phenomenon under normal conditions, but if fresh water is enclosed in a shell, for example, in a rubber ball, then this is clearly visible, since this ball floats to the surface. Our body is also a kind of shell filled with fresh water. We are made up of 45% to 75% water - this percentage decreases with age and with an increase in weight and body fat. Fat content of at least 5% of body weight. Healthy people have up to 10% body fat if they exercise a lot, up to 20% if they are of normal weight, and 25% or more if they are obese.

If we try not to swim, but simply to stay on the surface of the water, we will notice that it is easier to do this in salt water, since its density is higher than the density of fresh water and the fat contained in our body. The concentration of salt in the Dead Sea is 7 times the average concentration of salt in the oceans of the world, and it is known throughout the world for the fact that people can easily float on the surface of the water and not drown. Although, to think that it is impossible to die in this sea is a mistake. In fact, every year people die in this sea. The high salt content makes water dangerous if it enters the mouth, nose, and eyes. If you swallow such water, you can get a chemical burn - in severe cases, such unfortunate swimmers are hospitalized.

Air density

Just as in the case of water, bodies with a density below that of air are positively buoyant, that is, they take off. A good example of such a substance is helium. Its density is 0.000178 g/cm³, while the density of air is approximately 0.001293 g/cm³. You can see how helium takes off in the air if you fill a balloon with it.

The density of air decreases as its temperature increases. This property of hot air is used in balloons. The balloon pictured in the ancient Mayan city of Teotihuocán in Mexico is filled with hot air that has a density less than that of the surrounding cold morning air. That is why the ball flies at a sufficiently high altitude. While the ball flies over the pyramids, the air in it cools down, and it is heated again with a gas burner.

Density calculation

Often the density of substances is indicated for standard conditions, that is, for a temperature of 0 ° C and a pressure of 100 kPa. In educational and reference manuals, you can usually find such a density for substances that are often found in nature. Some examples are shown in the table below. In some cases, the table is not enough and the density must be calculated manually. In this case, the mass is divided by the volume of the body. Mass is easy to find with a balance. To find out the volume of a standard geometric body, you can use formulas to calculate the volume. The volume of liquids and solids can be found by filling the measuring cup with the substance. For more complex calculations, the liquid displacement method is used.

Liquid displacement method

To calculate the volume in this way, first pour a certain amount of water into a measuring vessel and place the body, the volume of which must be calculated, until completely immersed. The volume of a body is equal to the difference between the volume of water without the body and with it. It is believed that this rule was derived by Archimedes. It is possible to measure volume in this way only if the body does not absorb water and does not deteriorate from water. For example, we will not measure the volume of a camera or fabric using the liquid displacement method.

It is not known how much this legend reflects real events, but it is believed that King Hieron II gave Archimedes the task of determining whether his crown was made of pure gold. The king suspected that his goldsmith had stolen some of the gold allocated for the crown and instead made the crown out of a cheaper alloy. Archimedes could easily determine this volume by melting the crown, but the king ordered him to find a way to do this without damaging the crowns. It is believed that Archimedes found the solution to this problem while taking a bath. Having plunged into the water, he noticed that his body displaced a certain amount of water, and realized that the volume of water displaced is equal to the volume of the body in water.

hollow bodies

Some natural and artificial materials are made up of particles that are hollow inside, or of particles so small that these substances behave like liquids. In the second case, an empty space remains between the particles, filled with air, liquid, or other substance. Sometimes this place remains empty, that is, it is filled with vacuum. Examples of such substances are sand, salt, grain, snow and gravel. The volume of such materials can be determined by measuring the total volume and subtracting from it the volume of voids determined by geometric calculations. This method is convenient if the shape of the particles is more or less uniform.

For some materials, the amount of empty space depends on how tightly packed the particles are. This complicates the calculations, since it is not always easy to determine how much empty space there is between particles.

Table of densities of commonly occurring substances in nature

Density and Mass

In some industries, such as aviation, it is necessary to use materials that are as light as possible. Since low density materials also have low mass, in such situations, try to use materials with the lowest density. So, for example, the density of aluminum is only 2.7 g/cm³, while the density of steel is from 7.75 to 8.05 g/cm³. It is due to the low density that 80% of aircraft bodies use aluminum and its alloys. Of course, at the same time, one should not forget about strength - today, few people make aircraft from wood, leather, and other light but low-strength materials.

In aircraft, composite materials are often used instead of pure metals, since, unlike metals, such materials have high elasticity at low weight. The propellers of this Bombardier Q400 aircraft are made entirely of composite materials.

Black holes

On the other hand, the higher the mass of a substance per given volume, the higher the density. Black holes are an example of physical bodies with a very small volume and a huge mass, and, accordingly, a huge density. Such an astronomical body absorbs light and other bodies that are close enough to it. The largest black holes are called supermassive.

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