At the solution of some physical tasks it is required to find body density. Sometimes density of a physical body needs to be determined also in practice, for example, to learn, it will drown or not. By the way, the human body can also be carried to physical bodies. And the concept "density" of a human body became current for a long time. So the "strong" person is usually called "dense", and the one who has the opposite constitution of a body – "friable".

## It is required to you

- calculator, scales, ruler, measured mug, table of density of substances.

## Instruction

1. To find density of a physical body, define of what substance or material it consists. Then take the table of density of substances and find in it the corresponding substance. So, for example, if the subject is made of aluminum, its density will be equal to 2.7 g/cm³.

2. If the body consists of several substances, then find density of each of them in the corresponding tables. To find body density in general, define a contribution of each substance to formation of density of a subject. For this purpose determine the volume or mass of each uniform part, and then count the weight and volume of all body.

3. Let, for example, the body consist of two the mass of m1 of parts and m2, respectively. Density of each part – ρ1 and ρ2. To find the average density of a body, find total amount: V = V1 + V2 = m1 * ρ1 + m2 * ρ2, and then divide into body lump (m = m1 + m2): ρ = V/m = (m1 * ρ1 + m2 * ρ2) / (m1 + m2), where: V – total amount of a body; V1 and V2 – the volume of the first and second part of a body respectively; m – body lump; m1 and m2 – the mass of the first and second part of a body respectively; ρ – the average density of a body; ρ1 and ρ2 – density of the first and second part of a body respectively.

4. If volumes (V1 and V2) of each part of a body and also their density are known, for calculation of density of a body use a similar formula: ρ = V/m = (V1 + V2) / (m1 + m2) = (V1 + V2) / (V1/ρ1 + V2/ρ2). Designations of parameters the same, as in the previous formula.

5. If material (substance) of which the body consists is unknown or has changeable density (for example, a tree which density depends on humidity) to find its density, determine its volume and divide into weight. That is use a formula: ρ = V/m. For this purpose, of course, it is necessary to count or measure the volume and body weight, but such method will yield the most exact result. If the body has the form of a simple geometrical figure, count its volume, having used the corresponding formulas of stereometry. Determine the volume of difficult bodies through the volume of the liquid which is forced out by them. Find body weight by means of weighing.