Properties of Matter (Density, Specific Gravity) - SS1 Physics Lesson Note

Change Class & Subject Change Topic & Year

Properties of matter, such as density and specific gravity, provide information about the physical characteristics and behaviour of substances. Let's explore these properties in more detail:

1. Density:

Density is a measure of how much mass is contained in a given volume of a substance. It quantifies how closely packed the particles or molecules of a substance are. The formula for density is:

Density (ρ) = Mass (m) / Volume (V)

The SI unit for density is kilograms per cubic meter (kg/m³), but other commonly used units include grams per cubic centimetre (g/cm³) and kilograms per litre (kg/L).

Key points about density:

Different substances have different densities. For example, lead is denser than water, so a given volume of lead will have a greater mass than the same volume of water.
Density is an intensive property, meaning it does not depend on the amount of substance present. For example, the density of gold remains the same regardless of the size of the gold sample.
Density can be used to identify substances. The density of a substance is often a characteristic property unique to that substance, allowing for its identification.
Density plays a role in determining whether an object will float or sink in a fluid. Objects with a density greater than the fluid will sink, while those with a density less than the fluid will float.

2. Specific Gravity:

Specific gravity is a dimensionless quantity that compares the density of a substance to the density of a reference substance, usually water. It is calculated by dividing the density of the substance by the density of the reference substance.

Specific Gravity = Density of Substance / Density of Reference Substance

Since it is a ratio of two densities, specific gravity does not have units.

Key points about specific gravity:

Specific gravity provides a relative measure of the density of a substance compared to another substance, typically water.
Specific gravity is often used to compare the densities of liquids and solids. For example, the specific gravity of a mineral sample can help identify the mineral by comparing it to known values.
The specific gravity of water is approximately 1, so substances with a specific gravity greater than 1 are denser than water, while those with a specific gravity less than 1 are less dense than water.

Both density and specific gravity are important properties used in various scientific, industrial, and engineering applications. They help determine the behaviour and characteristics of substances and aid in material selection, buoyancy calculations, and quality control processes.