Physical property

Types: intensive and extensive

Physicists and chemists commonly group physical properties into two broad classes based on whether they depend on the amount of material present.

• Intensive properties do not change with sample size. Examples include temperature, color, density, hardness and electrical conductivity. Properties such as the speed or quickness of an object (used here in the sense of a measured rate) are likewise independent of amount when considered as a characteristic value.
• Extensive properties scale with how much substance is present. Total volume, total mass and weight are typical examples: if you double the sample, these quantities generally double as well.

Common physical properties and what they tell us

Physical properties fall into categories such as geometric (length, area, volume), mechanical (hardness, elasticity, tensile strength), thermal (temperature, heat capacity, melting point), electrical (resistivity, conductivity), optical (refractive index, color, transparency) and transport (diffusivity, viscosity). Some properties are fundamental—length, mass, time—used to define units; others are derived combinations of fundamentals. Density is an important derived quantity: it is intensive even though it depends on two extensive quantities (mass and volume).

Measurement, representation and use

Measurements of physical properties use instruments and standardized procedures so results are comparable. Values are reported with units and, when appropriate, uncertainties. Physical properties are used to select materials for applications, to design processes, and to predict behavior: engineers use strength and conductivity data; chemists and biologists rely on solubility and diffusivity; meteorologists measure temperature and pressure to describe weather systems. Some properties are constant under specified conditions (e.g., a pure substance's boiling point at a given pressure), while others change with environment and must be reported together with the conditions used.

Relation to chemical properties and notable distinctions

Physical properties differ from chemical properties, which describe how a substance transforms or reacts to produce new substances (for example flammability, oxidation behavior, or acidity). Observing a physical property should not change the substance's chemical identity; by contrast, a chemical test does. A few measurements sit between these categories: for example, heating a material to determine its melting point may induce decomposition in some compounds, which blurs the distinction unless care is taken.

Historically, the systematic classification of physical properties became central to thermodynamics and material science, where distinguishing intensive and extensive variables helps formulate conservation laws and equations of state. In practice, understanding which properties are intensive or extensive, how they are measured, and how they depend on conditions is essential across science and industry for quality control, material selection, and predicting performance.

For further reading see measurement and standards resources and topic-specific references linked here: definitions, terminology, dynamics, rates, volumetric, mass, and weight.