How to find a middle density. Determination of the average density of a dense sample of an improper geometric shape

Most bodies have a complex structure, because they consist of various substances. Therefore, find them density With the help of tables is almost impossible. To get an idea of \u200b\u200btheir structure, use such a thing as the average densitywhich is calculated after measuring the mass and volume of the body.

You will need

• - scales;
• - measuring cylinder;
• - Table of densities of various substances.

Instruction

If the body does not consist of a homogeneous substance, find it with the help of weights its mass, and then measure the volume. If it is a liquid, measure using a measuring cylinder. If that solid The correct form (cube, prism, polyhedron, ball, cylinder, etc.), find it with geometric methods. If the body is irregular, immerse it into the water, which is filled into a measuring cylinder, and by submitting it to determine the volume of the body. Divide the measured body weight on its volume, as a result you get the average density Body? \u003d m / v. If the mass was measured in kilograms, express the volume in m?, If in grams - in cm?. Respectively density Will it turn out in kg / m? Or g / cm?.

If weighing the body is not possible, find out density Materials from which it consists, then measure the volume of each component of the body. Then find the masses of the materials from which the body consists, moving their density to the volumes and the total volume of the body, by creating the volume of its component parts, including voids. Divide the total weight of the body on its volume, and get the average density Body? \u003d (? 1 v1 +? 2 v2 + ...) / (v1 + v2 + ...).

If the body can be immersed in water, find its weight in water using a dynamometer. Determine the volume of pinched water, which will be equal to the volume of the body immersed in it. When calculating, consider that density Water is 1000 kg / m?. To find medium density Bodies immersed in water, to his weight in Newton, add the number of 1000 numbers ( density Water) to accelerate the free fall 9.81 m / s? and the volume of the body in m? The resulting number will divide the volume of body volume and 9.81? \u003d (P +? In v 9,81) / (9.81 V).

When the body floats in water, find the volume of the pinched fluid, the volume of the body. Then average density The bodies will be equal to the ratio of the product of the water density onto it pushed the volume and volume of the body itself? \u003d? in VT / VT.

Average number - This is the average number of employees for a certain period of time. The report on this indicator takes all organizations to the Tax Inspectorate annually until January 20 for the previous year and when creating (liquidation) of the enterprise until the 20th day of the next month.

You will need

• Tabel of working time

Instruction

This report surrenders in the form of the CU-1110018 "Information on the average number of employees for the previous calendar year." Average number The organization's employees are very important when passing the following forms of tax reporting: VAT, income tax, property tax, land tax, and upon receipt of the right to switch to a simplified tax system.

First, determine this indicator for every day. It takes into account all in fact working and non-working, missing for any reason. Persons who have not exceeded full-time, are considered proportional to the number of spent time.

Then fold the number of employees for the entire month and divide the number of calendar days this month.

Next, summarize the average indicator for each month and divide the number 12 (number of months per year). The resulting digit and will be - average number workers for the calendar year.

In the middish number Even those who work under the employment contract and seasonal workers are included. Employees for whom for good reasons reduced the duration of working time, are considered as one-piece units. Employees working under the employment contract, but those listed in another organization can not be included in the average number of employee numbers. The number of employees should be indicated in the operating time tables in form No. T-12 or T-13.

The basis of this test also lies with the technical method for determining the volume of material samples, but in a natural (natural) state, including the pore volume and void, which depends on their geometric shape. Humidity is influenced by the average density, so the standards set a certain value of humidity at the time of testing for each material. It is recommended to determine the average density on samples of natural humidity or in a dry state (dried to constant mass at 105-110 0 s).

Main equipment

Callercircular or metal line, technical scales VLT-1kg, volume meter (Fig. 2.2), hydrostatic scales (Fig. 2.3), technical, thermostat.

Fig. 2.3. Hydrostatic scales:

1 - perforated (net) container; 2 - vessel with drain for water; 3 - rocker; 4 - Cup for multiple; 5 - a cup with a fraction; 6 - Removal

Testing

There are two standard definition methods. middle density: On samples of correct and improper geometric shape. They differ in the measurement method.

The volume of the sample of any proper geometric shape (cube, parallelepiped, cylinder) is calculated according to the results of direct measurements of the caliper with an error of up to 0.1 mm for dense samples (size 50-100 mm) or a metal ruler with an error of up to 0.5 mm for porous samples ( size more than 100 mm). The final size is found as the average arithmetic results of three dimensions (for the cylinder - four dimensions).

The volume of the sample of an irregular geometric shape (weighing more than 300-500 g) is determined using a size meter or hydrostatic weighing.

The test dry sample is pre-coated with a thin layer of molten at 75-85 0 from paraffin with a brush or immersion, weighed. You can pre-saturate the sample with water, remove an excess of it from the surface with a soft cloth and immediately determine the volume.

When testing using a size meter (see Fig. 2.2), a sample tied with a durable thread is carefully immersed in water. After the drop drops from the tube into the glass stops, it is weighed and calculated the mass of the displaced water. The volume of the sample is calculated by the formula

and without paraffining

Here - the mass of dry sample;

Paraffin-covered sample weight;

Mass of displaced water;

Paraffin density, \u003d 0.93 g / cm 3.

When using the hydrostatic weighing method, the sample volume is numerically equal to the value of the poverty force. Pre-prepared paraffinating or saturation in water, the sample material of a certain mass is weighed in a vessel with water on hydrostatic scales (Fig. 2.3). The volume of the sample is

and without paraffining

General properties of building materials " –

Definition physical properties Materials

True density is a mass of a substance contained in a unit of volume without internal pores and voids (in absolutely dense state) (,). It is calculated by the formula:

where m. - Material mass; V. - Volume of absolutely dense material.

The average density is the mass of the volume of material in natural condition Together with pores and voids (,):

where m.- mass of material, kg; V E.- the volume of material in the natural state ,.

In contrast to the true average density of various building materials fluctuates in very wide limits due to the presence of pores and emptiness, the content of which can reach 90% of the total volume. For example, for true density Quartz 2650 The average density of silicate wool (glass gamble, slag) can be 100 (applications 1 and 2). Thus, the average density of materials is always less than their true density. Only for absolutely dense materials (glass, steel, bitumen and other) the values \u200b\u200bof the average and true density coincide.

Most building materials have pores. Than they are more per unit volume of material, the less its density. For liquids and materials obtained from molten masses (glass, metal), the average density is virtually equal to true density.

The numerical value of density depends on chemical composition, crystalline structure and species building material and products. From the density of the material, its physicomechanical properties, such as strength and thermal conductivity, are largely dependent. The value of the material density is used in determining its porosity, mass and size building structures, transportation calculations and lifting and transport equipment. When determining the average material density, samples of both the correct and incorrect geometric shape can be used. The method of determining the average density of the material depends on the form of the sample.

Determining the average density of samples correct

Geometric shape

Determine the name of the material. Samples weighed and determine their geometric sizes with a caliper or a ruler with an accuracy of 0.1 cm:

a) for a sample having a cube form, a parallelepiped, volume V is calculated as a product of the base area to height;

b) for a sample of a cylindrical form volume V is calculated by the formula:

where V. - Sample volume, ().

Determine the average material density with an accuracy of 0.01. The results of the experiments contribute to Table 1.

Table 1. Results of determining the average density of samples of proper geometric shape

Determination of the average density of a dense sample of an improper geometric shape

The dry sample is weighed with an accuracy of 0.1 g and tied with thread. The measuring cylinder is filled with water, the volume of water is initial to immerse a sample, and after immersing the sample, the volume of water displaced them. The average sample density is determined by the formula:

The results are contributed in Table 2.

Table 2. Results of determining the average density of a dense sample of an irregular geometric shape