How is the density of a material measured? Density of various materials. Density of a substance: formula, definition and dependence on temperature

Instructions

Knowing the two above values, you can write the formula for calculating the density substances: density = mass / volume, hence the desired value. Example. It is known that an ice floe with a volume of 2 cubic meters weighs 1800 kg. Find the density of ice. Solution: Density is 1800 kg/2 meters cubed, resulting in 900 kg divided by cubic meters. Sometimes you have to convert density units to each other. In order not to get confused, you should remember: 1 g/cm3 cubed is equal to 1000 kg/m3 cubed. Example: 5.6 g/cm3 cubed is equal to 5.6*1000 = 5600 kg/m3 cubed.

Water, like any liquid, cannot always be weighed on a scale. But find out mass may be necessary both in some industries and in ordinary everyday situations, from calculating tanks to deciding how much reserve water you can take it with you in a kayak or rubber boat. In order to calculate mass water or any liquid placed in a particular volume, first of all you need to know its density.

You will need

• Measuring utensils
• Ruler, tape measure or any other measuring device
• Vessel for pouring water

Instructions

If you need to calculate mass water in a small vessel, this can be done using ordinary scales. First weigh the vessel along with. Then pour the water into another container. After this, weigh the empty vessel. Subtract from a full vessel mass empty. This will be contained in the vessel water. This way you can mass not only liquid, but also bulk, if it is possible to pour them into another container. This method can sometimes still be observed in some stores where there is no equipment. The seller first weighs the empty jar or bottle, then fills it with sour cream, weighs it again, determines the weight of the sour cream, and only after that calculates its cost.

In order to determine mass water in a vessel that cannot be weighed, you need to know two parameters - water(or any other liquid) and the volume of the vessel. Density water is 1 g/ml. The density of another liquid can be found in a special table, which is usually found in reference books.

If there is no measuring cup into which you can pour the water, calculate the volume of the vessel in which it is located. The volume is always equal to the product of the area of ​​the base and the height, and with vessels of a constant shape there are usually no problems. Volume water in the jar will be equal to the area of ​​the round base by the height filled with water. By multiplying the density? per volume water V, you will receive mass water m: m=?*V.

Video on the topic

Please note

You can determine the mass by knowing the amount of water and its molar mass. The molar mass of water is 18 because it consists of the molar masses of 2 hydrogen atoms and 1 oxygen atom. MH2O = 2MH+MO=2 1+16=18 (g/mol). m=n*M, where m is the mass of water, n is the quantity, M is the molar mass.

All substances have a certain density. Depending on the occupied volume and the given mass, the density is calculated. It is found based on experimental data and numerical transformations. In addition, density depends on many different factors, due to which its constant value changes.

Instructions

Imagine that you are given a vessel filled to the brim with water. The problem requires finding the density of water without knowing either the mass or volume. In order to calculate the density, both parameters must be found experimentally. Start by determining the mass.
Take the vessel and place it on the scale. Then pour the water out of it, and then place the vessel on the same scale again. Compare the measurement results and get a formula for finding the mass of water:
mob.- mс.=mв., where mob. - mass of the vessel with water (total mass), mс - mass of the vessel without water.
The second thing you need to find is water. Pour the water into a measuring vessel, then use the scale on it to determine the volume of water contained in the vessel. Only after this, use the formula to find the density of water:
ρ=m/V
This experiment can only approximately determine the density of water. However, under the influence of certain factors it can. Familiarize yourself with the most important of these factors.

At water temperature t=4 °C, water has a density ρ=1000 kg/m^3 or 1 g/cm^3. When this changes, the density also changes. In addition, factors affecting density

Formulas used in physics problems involving density, mass and volume.

Density is equal to the ratio of the mass of a body to its volume. Density is denoted by a Greek letter ρ (ro).

EXAMPLES OF SOLVING PROBLEMS

Task No. 1. Find the density of milk if 206 g of milk occupy a volume of 200 cm3?

Task No. 2. Determine the volume of a brick if its mass is 5 kg?

Task No. 3. Determine the mass of a steel part with a volume of 120 cm3

Problem No. 4. The dimensions of two rectangular tiles are the same. Which one has the most mass if one tile is cast iron and the other is steel?

Solution: From substance density tables (see at the end of the page) we determine that the density of cast iron ( ρ 2 = 7000 kg/m 3) less than the density of steel ( ρ 1 = 7800 kg/m 3). Consequently, a unit volume of cast iron contains less mass than a unit volume of steel, since the lower the density of a substance, the less its mass if the volumes of the bodies are the same.

Problem No. 5. Determine the density of chalk if the mass of a piece of it with a volume of 20 cm 3 is equal to 48 g. Express this density in kg/m 3 and in g/cm 3.

Answer: Chalk density 2.4 g/cm 3, or 2400 kg/m 3.

Task No. 6. What is the mass of an oak beam with a length of 5 m and a cross-sectional area of ​​0.04 m 2?

ANSWER: 160 kg.

SOLUTION. From the formula for density we obtain m = p V. Taking into account the fact that the volume of the beam V = S l, we get: m = pS l.

We calculate: m = 800 kg/m 3 0.04 m 2 5 m = 160 kg.

Task No. 7. A block whose mass is 21.6 g has dimensions 4 x 2.5 x 0.8 cm. Determine what substance it is made of.

ANSWER: The bar is made of aluminum.

Task No. 8 (increased difficulty). A hollow copper cube with an edge length a = 6 cm has a mass m = 810 g. What is the thickness of the walls of the cube?

ANSWER: 5 mm.

SOLUTION: Volume of the cube V K = a 3 = 216 cm 3. Wall volume V C can be calculated by knowing the mass of the cube m K and copper density r: V C = m K / r = 91 cm 3. Therefore, the volume of the cavity V P = V K - V C = 125 cm 3. Because 125 cm 3 = (5 cm) 3, the cavity is a cube with edge length b = 5 cm. It follows that the thickness of the walls of the cube is equal to (a - b)/2 = (6 – 5)/2 = 0.5 cm.

Problem No. 9 (Olympiad level). The mass of a test tube with water is 50 g. The mass of the same test tube filled with water, but with a piece of metal weighing 12 g in it is 60.5 g. Determine the density of the metal placed in the test tube.

ANSWER: 8000 kg/m 3

SOLUTION: If some of the water from the test tube had not poured out, then in this case the total mass of the test tube, water and a piece of metal in it would be equal to 50 g + 12 g = 62 g. According to the conditions of the problem, the mass of water in a test tube with a piece of metal in it is equal to 60.5 g. Therefore, the mass of water displaced by the metal is equal to 1.5 g, i.e., it is 1/8 of the mass of the piece of metal. Thus, the density of metal is 8 times greater than the density of water.

Problems on density, mass and volume with solutions. Table of density of substances.

In industry and agriculture, there is a need to know the density of the substances used, for example, the mass and volume of concrete is calculated by concrete workers based on its density when pouring foundations, columns, walls, bridge supports, slopes, dams, etc. The density of a substance is a physical quantity that characterizes body weight divided by its volume.

It is assumed that the body is continuous, without voids or admixtures of other substances. This value for various substances is reflected in reference tables. But it is interesting to know how such tables are filled out, how the density of unknown substances is determined. The simplest ways to determine the density of substances:

For liquids using a hydrometer;

For liquids and solids by measuring volume and mass and calculating using the formula.

Sometimes, due to the irregular shape of bodies or their large size, it is difficult or even impossible to determine their volume using a ruler or beaker. Then the question arises, how can one determine their density without resorting to measuring volume, or is it not possible to determine the mass of a substance?

Purpose of work: Solving experimental problems to determine the density of various substances.

Objectives: 1) Study various methods for determining the density of a substance described in the literature

2) Measure the density of some substances using methods proposed in the literature and evaluate the error limits of each method

3) Determine the density of the unknown substance based on the identified methods.

4) Present in the form of tables the density of solutions of salt, sugar and

4 copper sulfate of varying concentrations.

Materials and research methods: Research was carried out with common substances: 10% salt solution, 10% copper sulfate solution, water, aluminum, steel, etc. For measurements, instruments of the 4th accuracy class were used: scales with weights, a hydrometer, communicating vessels from a liquid pressure gauge, as well as a set of calorimetric bodies. The experiments were carried out at room temperature (20-250C), in a school building, in a physics classroom.

5 11. 3. Determination of liquid density a) Method of weighing a body in air and an unknown liquid

Purpose: Determine the density of the liquid (copper sulfate solution). The density ρ0 of water is 1000 kg/m.

Instruments: Dynamometer, thread, vessel with water, vessel with unknown liquid, body from a set of calorimetric bodies.

Progress: Using a dynamometer, we determine the weight of the body in air (P1), in water (P2) and in an unknown liquid (P3).

FA=ρgV - force

Archimedes The Archimedes force acting on a body in water is equal to

FA=P1-P2, and in an unknown liquid:

According to Archimedes' law, we write

P1-P2=ρ0Vg, (1)

Solving the system of equations (1) and (2), we find the density of the unknown liquid:

ρ=(P1-P3)/Vg, V=(P1-P2)/ρ0g, ρ=(P1-P3/P1-P2)ρ0.

ρ= (1H-0.6H/1H-0.7H)1000 kg/m3 = 400H kg/m3/0.3H=1333.(3) kg/m3 b) Comparison method with water density

Equipment: Communicating vessels made of glass tubes (with a scale), rubber tube, beaker, pipette, flasks (or glass jars) with various liquids.

Work progress: 1. Put a rubber band on one end of the communicating vessels.

6 tube (after clamping the last one so that air does not enter the communicating vessels through it).

2. Using a pipette, the test liquid is poured into communicating vessels (to a certain level).

3. Pour (to a certain level) distilled water into the beaker.

4. The free end of the rubber tube is immersed (to the bottom) in a beaker (Fig. 1). In this case, the fluid level in the elbows of the communicating vessels will change (let h1 be the difference in levels in the elbows)

5. The liquid being tested is poured out of the communicating vessel and distilled water is poured in its place to the previous level.

6. Having poured water from the beaker, pour the test liquid into it to the previous level.

7. Again immerse the free end of the rubber tube into the beaker and again find the difference in levels.

Since the height of the liquid level is inversely proportional to its density, we can write: h1/h2 = ρx/ρв, or ρВ=h2ρВ/h1, where ρВ and ρX are the densities of distilled water and the liquid under study, respectively.

h1= 3.5 cm h2= 5 cm

ρX= 5 cm / 3.5 cm 1000 kg/m3 = 1428 kg/m3

Thus, knowing the density of the liquid, we can find out what kind of liquid we studied. In this case it is copper sulfate.

7 2. Determination of the density of a solid a) Method of weighing a sample in air and water

Equipment: Scales with weights, a 0.5 liter glass, threads and pieces of wire, test samples (pieces of aluminum, tin, granite, wood, plexiglass plate, cork).

Method of performing the work: The proposed method allows you to determine the density of any substance (having a density greater or less than that of water) by weighing a sample in air and water.

Let m1 be the mass of the body under study. Then its weight in the air can be found like this:

Р =m1g, (1) where g is the acceleration of free fall. Submerged in water this body has weight

Here FA is the Archimedean force:

(V is the volume of water displaced by the body, ρВ is its density).

Balancing the scales, we get:

P2=m2g, (4) where ta is the mass of the weights that must be placed on the left pan to balance the scales. From (1) - (4) we get: m2=m1-ρвV (5)

Since volume V is equal to the volume of a body immersed in water, we can write:

V=m1/ρx (6) where ρx is the density of the substance that makes up the body under study. From (5) and (6) we find:

ρx=m1/(m1-m2)ρв (7)

Work order:

/. The density of the bodies under study is greater than the density of water.

1. Determine the mass m1 of the body under study.

2. Tie the body under study with a thread to the left pan of the scale and lower it into a glass of water (until completely immersed).

3. Weights of mass m2 necessary to balance the scales are placed on the same cup.

4. Using formula (7), the density ρx of the body under study is determined. The measurement results are recorded in Table 1.

Table 1

Substance m1, 10-3 m2, 10-3 ρx, 103 ρy, 103 ε, %

kg kg kg m-3 kg m-3

Aluminum 21.85 13.65 2.664 2.698 1.2

Tin 62.4 53.85 7.2982 7.298 0.003

Granite 17.35 10.75 2.628 2. 5-3 5

Plexiglas 3.75 0.75 1.23 1.18 4.2

ΙΙ. The density of the bodies under study is less than the density of water.

1. Measure the mass m1 of the body under study.

2. The body is rigidly attached to the left pan of the scale using three pieces of copper wire (0.5 - 0.7 mm in diameter; two pieces 10 - 15 cm long, one - 30 - 35 cm). To do this, their ends are twisted into a bundle, in which a steel needle (or a piece of rigid, pointed wire) is secured, and the upper ends of the short wires are attached to the protrusions of the scale cup (Fig. 2).

Balance the scales. Then the body under study is pinned on a needle.

3. The body is completely immersed in water, and weights of mass m2 are added to the left pan of the scale and the balance is achieved. According to the formula

ρx=m1/(m1+m2)ρx find the density of the body under study. The measurement results are recorded in Table 2.

Table 2

substance m3.10-3 m2.10-3 kg pх, 103 kgm-3 ρy, table. ε,%

Cork Wood 3.7 22.5 0.14 0.2 30

20 25 0.44 0.45 2.2 b) Method based on the floating conditions of bodies.

Equipment: a piece of plasticine, a cylindrical vessel with water

(ρ = 1 g/cm3), ruler.

Work progress: 1. We immerse a piece of plasticine in a vessel with water and measure with a ruler the changes in the level h1 of the liquid in the vessel.

2. We make a “boat” from plasticine and let it float in a vessel with water. We again measure the change in the level h2 of the liquid.

3. Find the density of plasticine using the formula:

ρlayer = mlayer/Vlayer = ρSh2 / Sh1 = ρВh2/h1

ρlayer = ρВh2/h1 h1 = 2mm h2 = 4mm

ρplast =1000 kg/m3 4mm / 2mm = 2000 kg/m3

Determining the density of an unknown substance

Goal: Determine the density of the unknown substance X in the solid state. Substance X does not dissolve in water and does not enter into chemical reactions with it.

Equipment: Glass beaker with water, test tube, measuring ruler, unknown substance X in the form of small pieces.

Work progress: First, we place only the unknown substance X into the test tube and note the depth H of the test tube immersion. Then we remove substance X from the test tube and pour in enough water so that the immersion depth of H in the second experiment is exactly the same as in the first experiment. In this case, the mass of water mв in the test tube in the second experiment is equal to the mass mх of the unknown substance in the first experiment: mв = mX

The density ρX of a substance X can be calculated using the equality ρX = mX/VX = mB/VX. To reduce possible measurement errors when determining the depth H of a test tube, we will use the following technique.

Pour enough water into the glass so that its level is approximately 1 cm below the rim. By loading the test tube with an unknown substance X in small portions, we will achieve a depth of immersion such that the upper edge of the test tube is at the level of the upper edge of the vessel. This position of the test tube can be determined with great accuracy using a ruler placed on top of the glass.

Having then replaced the unknown substance with water, we will achieve exactly the same immersion depth of the test tube by gradually adding water to it.

Let's measure the height h1 of the water level in the test tube. The volume of water in the test tube is

VВ= Sh1, where S is the internal cross-sectional area of ​​the test tube. Let's lower the unknown substance used earlier in the experiment into a test tube with water and measure the height of the water level h2 in it. The volume of the substance Vx is expressed through the area S of the internal cross-section of the test tube and the change in the height of the water level h2 - h1 in the test tube when the substance is lowered into water:

The density of matter ρX is equal to

ρX = mX/VX = mВ/VX = ρВВВ/VX=ρВSh1/(S(h2-h1)),

ρX = ρВh1/(h2-h1).

h1 =3. 3 cm h2= 3.8 cm

ρX = 1000kg/m3

ρX =1000kg/m3 3.3 cm/(3.8 cm-3.3 cm) = 3.3 cm

1000 kg/m3 / 0.5 cm = 6.6 cm 1000 kg/m3 = 6600 kg/m3

Comparing our result with the tabular data, we can assume that the unknown substance is zinc.

Determination of the density of liquids of different concentrations

Purpose: Determine the densities of solutions of salt, sugar and copper sulfate of different concentrations. Create tables based on the data obtained. Equipment: Scales with weights, test tube (250 ml), aluminum cup.

Substances: Sugar, salt, copper sulfate. Work progress: a) Saline solution

In order to obtain a solution with different concentrations, you need to add one teaspoon (5.6 g) of salt to the water. After each spoon, you need to measure the weight and volume of the resulting solution, taking into account that m glass = 44.75 g.

In chemical laboratories it is very often necessary to determine density. In the literature of previous years and in reference books of old publications, tables of the specific gravities of solutions and solids are given. This quantity was used instead of density, which is one of the most important physical quantities that characterize the properties of matter.

The density of a substance is the ratio of the mass of a body to its volume:

Therefore, the density of a substance is expressed * in g/cm3. Specific gravity y is the ratio of the weight (gravity) of a substance to its volume:

The density and specific gravity of a substance are in the same relationship with each other as mass and weight, i.e.

where g is the local value of the acceleration due to gravity during free fall. Thus, the dimensions of specific gravity "(g/cm2 sec2) and density (g/cm3), as well as their numerical values ​​expressed in the same system of units, differ from each other *.

The density of a body does not depend on its location on Earth, while its specific gravity varies depending on where on Earth it is measured.

In some cases, they prefer to use the so-called relative density, which is the ratio of the density of a given substance to the density of another substance under certain conditions. Relative density is expressed as an abstract number.

The relative density d of liquid and solid substances is usually determined in relation to the density of distilled water:

It goes without saying that p and pb must be expressed in the same units.

Relative density d can also be expressed as the ratio of the mass of a substance taken to the mass of distilled water taken in the same volume as the substance, under certain, constant conditions.

Since the numerical values ​​of both relative density and relative specific gravity under the specified constant conditions are the same, you can use tables of relative specific gravity in reference books in the same way as if they were density tables.

Relative density is a constant value for each chemically homogeneous substance and for solutions at a given temperature. Therefore, according to

* In some cases, density is expressed in g/ml. The difference between the numerical density values ​​expressed in g/cm3 and g/ml is very small. It should be taken into account only when working with extreme precision.

Therefore, in many cases, the relative density can be used to judge the concentration of a substance in a solution.

* In the technical system of units (MKXCC). in which the basic unit is not a unit of mass, but a unit of force - kilogram-force (kg or kgf), specific gravity is expressed in kg / m3 or G / cm3. It should be noted that the numerical values ​​of specific gravity, measured in G/cm3, and density, measured in g/cm3, are the same, which often causes confusion in the concepts of “density” and “specific gravity”.

Typically, the density of a solution increases with increasing concentration of the solute (if the solute itself has a density greater than the solvent). But there are substances for which the increase in density with increasing concentration goes only up to a certain limit, after which the density decreases with increasing concentration.

For example, sulfuric acid has the highest density of 1.8415 at a concentration of 97.35%. A further increase in concentration is accompanied by a decrease in density to 1.8315, which corresponds to 99.31%.

Acetic acid has a maximum density at a concentration of 77-79%, and 100% acetic acid has the same density as 41%.

Relative density depends on the temperature at which it is determined. Therefore, they always indicate the temperature at which the determination was made and the temperature of the water (volume taken as a unit). In reference books this is shown using appropriate indexes, for example eft; the given designation indicates that the relative density was determined at a temperature of 2O0C and the density of water at a temperature of 4°C was taken as a unit for comparison. There are also other indices indicating the conditions under which the relative density was determined, for example R4 Ul, etc.

The change in relative density of 90% sulfuric acid depending on the ambient temperature is given below:

The relative density decreases with increasing temperature, and increases with decreasing temperature.

When determining the relative density, it is necessary to note the temperature at which it was carried out, and compare the obtained values ​​with tabular data determined at the same temperature.

If the measurement was not carried out at the temperature indicated in the reference book, then. a correction is introduced, calculated as the average change in relative density per degree. For example, if in the interval between 15 and 20 0C the relative density of 90% sulfuric acid decreases by 1.8198-1.8144 = 0.0054, then on average we can assume that with a temperature change of 1 0C (above 15 0C) relative density decreases by 0.0054: 5 = 0.0011.

Thus, if the determination is carried out at 18 0C, then the relative density of the specified solution should be equal to:

However, to introduce a temperature correction to the relative density, it is more convenient to use the nomogram below (Fig. 488). This nomogram, in addition, makes it possible for the known relative density, calculated at a standard temperature of 20 ° C, to approximately determine the relative density at other temperatures, which may sometimes be necessary. The relative density of liquids can be determined using hydrometers, pycnometers, special balances and etc.

Determination of relative density using hydrometers.

To quickly determine the relative density of a liquid, so-called hydrometers are used (Fig. 489). This is a glass tube (Fig. 489, a), expanding at the bottom and having at the end a glass reservoir filled with shot or a special mass (less often - mercury). In the upper narrow part of the hydrometer there is a scale with divisions. The lower the relative density of the liquid, the deeper the hydrometer sinks into it. Therefore, on its scale, the smallest relative density value that can be determined by this hydrometer is indicated at the top, and the largest at the bottom. For example, for hydrometers for liquids with a relative density less than one, the value below is 1.000, above 0.990, even above 0.980, etc.

The spaces between the numbers are divided into smaller divisions, allowing the relative density to be determined with an accuracy of up to the third decimal place. For the most accurate hydrometers, the scale covers relative density values ​​in the range of 0.2-0.4 units (for example, to determine density from 1,000 to 1,200, from 1,200 to 1,400, etc.). Such hydrometers are usually sold in the form of kits, which make it possible to determine relative density over a wide range.

Nomogram for introducing temperature correction

Sometimes hydrometers are equipped with thermometers (Fig. 489.6), which makes it possible to simultaneously measure the temperature at which the determination is carried out. To determine the relative density using a hydrometer, the liquid is poured into a glass cylinder (Fig. 490) with a capacity of at least 0.5 liters, similar in shape to the measuring cylinder, but without a spout or divisions. The size of the cylinder must match the size of the hydrometer. You should not pour liquid into the cylinder to the brim, since when the hydrometer is immersed, the liquid may overflow. This can even be dangerous when measuring the density of concentrated acids or concentrated alkalis, etc. Therefore, the liquid level in the cylinder should be several centimeters below the edge of the cylinder.

Sometimes the cylinder for determining density has a groove at the top, located concentrically, so that if the liquid overflows when the hydrometer is immersed, it will not spill out onto the table.

To determine the relative density, there are special instruments that maintain a constant level of liquid in the cylinder. A diagram of one of these devices is shown in Fig. 491. This is a cylinder 2, which has an outlet tube 3 at a certain height for draining the liquid displaced by the hydrometer when it is immersed in the liquid. The displaced liquid enters tube 4, which has a tap 5, through which the liquid can be drained. The cylinder can be filled with the test liquid through an equalizing tube /, which has a cylindrical extension in the upper part.

§ 9. What is the density of matter?

What do they mean when they say: heavy as lead or light as feathers? It is clear that a grain of lead will be light, and at the same time, a mountain of fluff will have a fair amount of mass. Those who use such comparisons do not mean the mass of bodies, but some other characteristic.

Often in life you can find bodies that have the same volume but different masses. For example, a tomato and a small ball. And the store has a large selection of goods that have equal masses but differ in volume, for example, a package of butter and a package of corn sticks. It follows from this that bodies of equal mass can have different volumes, and bodies of the same volume can differ in mass. This means that there is a certain physical quantity that connects both of these characteristics. This quantity was called density (denoted by the letter of the Greek alphabet ρ - rho).

Density is a physical quantity numerically equal to the mass of 1 cm3 of a substance. Density unit kg/m3 or g/cm3. Thus, the density of a substance does not change under constant conditions and does not depend on the volume of the body.

There are several ways to determine the density of a substance. One of these methods is to determine the mass of a substance by weighing and measuring the volume it occupies. Using the obtained values, you can calculate the density by dividing the mass of the body by its volume.

Body weight T

Density = ----- or ρ = --

Body volume V

The density of a substance does not always need to be calculated. So, to measure the density of a liquid there is a device - hydrometer. It is immersed in a liquid. Depending on the density of the liquid, the hydrometer is immersed in it to different depths.

Knowing the density of the substance and the volume of the body, you can calculate the mass of the body and do without scales, t = V* ρ

Knowing the density of a substance and the mass of a body, it is easy to calculate its volume.

V=m/ρ

This is very convenient when the shape of the body being studied is complex, for example, a snail shell or a fragment of a mineral.

A little history. It was in this way that the famous Archimedes caught the Syracuse jeweler in a lie, who made a crown not made of pure gold for King Heron 250 years BC. The density of the corona material turned out to be less than the density of gold. The jeweler had no idea about the revelation, because the shape of the crown was incredibly complex.

The densities of various substances are determined and entered into special tables. You have such a table in your workshop notebook on page 22.

From the table given in the workshop notebook it is clear that substances in the gaseous state have the lowest density; the greatest - substances in the solid state. This is explained by the fact that molecules in gases are located far from each other, and molecules in solids are close. Therefore, the density of a substance is related to how close or far away the molecules are. And the molecules themselves of different substances differ both in mass and in size.

Different substances have different densities, which depend on the mass and size of the molecules, as well as on their relative position. The density of a substance can be calculated by knowing its mass and body volume. To measure the density of liquids, there is a device called a hydrometer, and special tables have been compiled to determine the density of various substances.

Hydrometer * Density of substances

Test your knowledge

1. What physical quantity is called the density of matter?

2. What quantities do you need to know to calculate the density of a substance?

3. What device can determine the density of a liquid? How is it built?

4. Using the table of density of substances, determine the density of: aluminum, distilled water, honey.

5. Using the table of substance density, name:

a) the substance with the highest density;

b) with the lowest density;

c) with a density greater than that of distilled water.

b. In nature, substances with different densities often interact. Using the table of substance densities, explain why:

a) ice is always located on the surface of the water;

b) a gasoline film floats on the surface of a puddle;

c) is it easier for a person to swim in sea water than in fresh water?