Dimensionless quantity

A physical quantity represented by a ratio of like dimensions, so its value has no physical dimension. It can still carry units such as radians or be expressed as a percentage.

Physical dimension: A classification of physical quantities by dependence on base quantities such as length, mass, and time. Dimensionless quantities have zero powers of every base dimension.
Buckingham π theorem: A theorem that reduces dimensional physical relationships to equations among dimensionless products of variables. It formalizes how dimensional variables can be combined into independent dimensionless groups.
Strouhal number: A dimensionless number relating oscillation frequency, characteristic length, and flow speed. It characterizes unsteady flow, including periodic vortex shedding.
Dimensionless constant: A fixed numerical value with no physical dimensions. Unlike a general dimensionless quantity, it does not vary with the system's state or conditions.
Dimensional analysis: The use of physical dimensions to check equations and derive relationships among quantities. It identifies dimensionless combinations and tests whether equations are dimensionally consistent.
Similarity analysis: A method for comparing systems by matching their governing dimensionless parameters. Matching these parameters lets models and full-scale systems exhibit corresponding behavior.
Prandtl number: The ratio of momentum diffusivity to thermal diffusivity in a fluid. It helps compare the thickness of velocity and temperature boundary layers.
Angle: A measure of rotation, commonly defined as the ratio of arc length to radius. Angles are dimensionless ratios, though radians remain useful named units.
SI base units: The seven mutually independent units used to define the International System of Units. Dimensions are expressed as powers of base quantities associated with these units.
Reynolds number: The ratio of inertial to viscous forces in a fluid flow. It is a dimensionless ratio that predicts whether flow tends to be laminar or turbulent.

Linked from 21 pages