ISO 80000-4:2019

Overview

ISO 80000-4:2019 - Quantities and units - Part 4: Mechanics is an international standard, prepared by ISO (with IEC collaboration), that defines the names, symbols, definitions and SI units for quantities used in mechanics. The document provides a standardized, authoritative reference for mechanical quantities (mass, force, stress, strain, torque, viscosity, etc.) and, where appropriate, gives conversion factors and notes on conditions of use. The 2019 second edition simplifies the main quantities table and refines several definitions for improved physical precision.

Key topics

This part of the ISO 80000 series covers the technical specification and notation conventions for mechanics, including but not limited to:

• Fundamental quantities: mass, mass density, specific volume, surface and linear mass density
• Kinematics & dynamics: momentum, impulse, force (including weight, friction, drag, rolling resistance), torque, power, energy
• Rotational quantities: moment of inertia tensor, angular momentum, angular impulse
• Continuum mechanics: stress tensor (normal and shear stress), strain tensor (linear, shear, volumetric), Poisson’s ratio
• Material properties: Young’s modulus, shear modulus, bulk modulus, compressibility
• Fluid-related quantities: dynamic viscosity, kinematic viscosity, drag coefficient, surface tension
• Geometrical/mechanical descriptors: second moments of area, section modulus
• Notational rules for tensors and vectors, units (SI base and derived), and requirements to specify conditions (e.g., isothermal/adiabatic) where material-dependent moduli or compressibility are used.

The standard also emphasizes consistent symbol usage, tensor symmetry (where applicable), and references to related parts of the ISO 80000/IEC 80000 series for kinematics, time, and energy definitions.

Applications and users

ISO 80000-4 is essential for:

• Mechanical, structural and aerospace engineers standardizing calculations, drawings and reports
• Metrology and testing laboratories that require unambiguous units and definitions
• Simulation and CAE/FEA software developers implementing physical quantity libraries and unit handling
• Technical authors, educators and standards committees preparing specifications and teaching materials
• Instrument manufacturers and calibration bodies ensuring consistent measurement traceability

Using ISO 80000-4 reduces ambiguity in documentation, facilitates international collaboration, and improves interoperability of engineering data, models and instruments.

Related standards

• ISO 80000 series (quantity and unit parts) - see ISO 80000-1, ISO 80000-2, ISO 80000-3, ISO 80000-5 for general rules, mathematical symbols, space/time and energy topics
• IEC/ISO terminological databases (ISO Online Browsing Platform, IEC Electropedia) for cross-references and definitions

Keywords: ISO 80000-4:2019, mechanics quantities, SI units, mechanical symbols, stress and strain, viscosity, torque, moment of inertia, standards for mechanics.