Density is defined as the mass per unit what?

• A. Mass per unit volume
• B. Weight per unit area
• C. Color, appearance
• D. Thermal conductivity

Answer: (A)

Density describes how much matter is packed into a given space. It is defined as mass per unit volume, written as ρ = m/V. This means that with the same mass, a smaller volume yields a higher density, while a larger volume yields a lower density. For example, a kilogram of metal takes up far less space than a kilogram of foam, so the metal is denser. The standard SI unit is kilograms per cubic meter.

Weight per unit area would relate to pressure, not density. Color or appearance tells you about an object's look, not how much matter it contains per volume. Thermal conductivity describes how easily heat moves through a material, not how much mass is present in a given volume. Thus density is all about mass divided by volume.