AQA GCSE FOUNDATION Physics: Density of Regular and Irregular Solids

AQA GCSE Foundation Physics: Density of Regular and Irregular Solids

This tutorial will guide you through the process of calculating the density of both regular and irregular solids.

What is Density?

Density is a measure of how much mass is contained in a given volume. It tells us how tightly packed the particles are within a material. The formula for density is:

Density = Mass / Volume

Calculating Density of Regular Solids

1. Measure the Mass: Use a balance to find the mass of the solid in grams (g).

2. Calculate the Volume: For regular solids (e.g., cubes, spheres, rectangular blocks), you can calculate the volume using the following formulas:

   • Cube: Volume = side x side x side
   • Sphere: Volume = (4/3) x ? x radius³
   • Rectangular Block: Volume = length x width x height

3. Calculate the Density: Divide the mass by the volume. The units of density are grams per cubic centimeter (g/cm³).

Example: A rectangular block of wood has a mass of 50g. Its length is 10cm, width is 5cm, and height is 2cm.

• Volume = 10cm x 5cm x 2cm = 100cm³
• Density = 50g / 100cm³ = 0.5 g/cm³

Calculating Density of Irregular Solids

1. Measure the Mass: Use a balance to find the mass of the irregular solid in grams (g).

2. Determine the Volume using Water Displacement:

   • Fill a measuring cylinder with a known volume of water.
   • Carefully lower the irregular solid into the cylinder, ensuring it is fully submerged.
   • Note the new water level.
   • The volume of the solid is the difference between the initial and final water levels.

3. Calculate the Density: Divide the mass by the volume.

Example: An irregular rock has a mass of 20g. When placed in a measuring cylinder containing 50ml of water, the water level rises to 65ml.

• Volume = 65ml - 50ml = 15ml = 15cm³ (1ml = 1cm³)
• Density = 20g / 15cm³ = 1.33 g/cm³

Comparing Densities

You can compare the densities of different materials to identify them. For example:

• Iron has a density of about 7.87 g/cm³
• Aluminum has a density of about 2.7 g/cm³
• Water has a density of about 1 g/cm³

If you measure the density of an unknown object and find it to be close to 7.87 g/cm³, it is likely made of iron.

Key Points

• Density is a characteristic property of a material. This means that every sample of a particular material will have the same density, regardless of its size or shape.
• Density is affected by temperature. Materials generally expand when heated, decreasing their density.
• Density plays a vital role in many natural phenomena. For example, it determines whether objects float or sink in water.

By understanding the concept of density and the methods for calculating it, you can gain valuable insights into the properties of various materials.