Density

Density is defined as the mass in a unit of volume.

Density

In the SI unit system, mass is measured in kg and volume is measured in m3, thus, the unit of density is kg/m3 (kilogram per cubic meter). But this is inconvenient for most substances, therefore, g/cm3 (gram per cubic centimeter) is a more common unit of density.

Unit of Density

Density is a characteristic property of matter. We can differentiate substances by using their densities.

Examples:

How to manipulate the formula

In order to calculate the density of an object, first we measure its mass with a scale, then we find its volume by measuring it with a ruler, if it has a regular shape. Otherwise we use the graduated cylinder method for irregular objects, and liquids. Then, by dividing mass by volume, we find the density of the object.

How can we calculate the density of an object?

What is the volume of 24 tons of cement? (dcement = 3000 kg/m3)

Calculate the mass of copper having the same volume as 31,5 g of silver. Use Table 1.7.

A bottle has a mass of 70 g when it is empty, 90 g when it is full of water and 96 g when it is full of a liquid. What is the density of the liquid in g/cm3 and kg/m3 ?

Calculate the mass of air (at 0° C) in a room having dimensions of 3 m, 6 m, 5 m. See Table 1.7.

The density of a mixture is found by dividing the total mass of the mixture by its total volume.

Density of a mixture

1.3 kg of a liquid and 2 kg of water are mixed in a container. Find the density of the mixture. Take dliquid = 1.3 g/cm3 and dwater = 1 g/cm3.

Two different substances of volumes 200 cm3 and 300 cm3 are mixed to make an alloy. If their densities are 1.2 g/cm3 and 1.6 g/cm3 respectively, find the density of the alloy.

Time

One complete rotation of earth around its axis is called one day. It is equal to 24 hours (h), 1 hour is 60 minutes (min) and 1 minute is 60 seconds (s). The unit of time is the second. A stopwatch or clock is used to measure time.

What is the equivalent of one week in terms of hours, minutes and seconds?