Density and Temperature PDF

## UNIT 7 DENSITY AND TEMPERATURE ### 7.1 DENSITY Density of a material tells us how much matter a substance has in its unit volume. The substance which has more closely packed atoms, has more matter in a fix volume. Therefore, it is denser substance. Solids like metals, rocks etc. are denser mate...

## UNIT 7 DENSITY AND TEMPERATURE ### 7.1 DENSITY Density of a material tells us how much matter a substance has in its unit volume. The substance which has more closely packed atoms, has more matter in a fix volume. Therefore, it is denser substance. Solids like metals, rocks etc. are denser materials because they have closely packed atoms in the given volume. Substances in which atoms are far from each other, they have small amount of matter in a fix volume, so they are less dense. It is the reason why liquids and gases have less density than solids. Density of solids is greater than liquids and density of liquids is greater than gases. ### FIGURE 7.1 STATES OF MATTER Solids have more atoms per unit volume than liquids and gases, so solids are denser than liquids and gases | | | | |---|---|---| | **Solids** | **Liquids** | **Gases** | We define density of a material as: "Mass per unit volume of the substance is called its density". Density = Mass / Volume Its symbol is so: p = m / V Its SI unit is kilogram per cubic metre (kg/m^3 ). Smaller unit to measure density is gram per cubic centimetre (g/cm^3). Density of liquids is usually measured in gram per millilitre (g/mL). It is a scalar quantity. Density of small amount of a substance is the same as the density of its bulk because density is calculated by the amount of matter in its unit volume. Density of a material changes with the temperature. Can you explain why? ### TABLE 7.1 DENSITY | Material | Density (kg/m^3) | |---|---| | Polyethylene | 7900 | | Petrol | 1930 | | Water | 920 | | Ice | 900 | | Wood | 800 | | Air | 100 | | Mercury | 136 | | Sea water | 1.3 | | Carbon dioxide | 2.0 | ### EXAMPLE 7.1: DENSITY Find a material in the options. Find the density of the material in the options. * Given: Mass of the cube, Side length * Required: Density of the cube, Volume of the cube * Solution: By putting values in the formula, we will find density Density of cube = Mass/Volume Putting values p = 12 / 4 = 3 kg/m^3 **DO YOU KNOW?** Osmium metal is the most dense material at room temperature and pressure. Its density is 22.59 g/cm^3 . It is harder than diamond. ### CAN YOU TELL? Why are liquids denser than gases? ### FOR YOUR INFORMATION 1 g/cm^3 = 1000 kg/m^3 To convert g/cm^3 into kg/m^3, multiply g/cm^3 by 1000. For example, the density of petrol, 0.9 g/cm^3, is multiplied by 1000 to write in units of kg/m^3 as 900 kg/m^3.