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In physics, a characteristic length is an important dimension that defines the scale of a physical system. Often, such a length is used as an input to a formula in order to predict some characteristics of the system, and it is usually required by the construction of a dimensionless quantity, in the general framework of dimensional analysis and in particular applications such as fluid mechanics.
= where is the relaxation time of the particle (the time constant in the exponential decay of the particle velocity due to drag), is the fluid velocity of the flow well away from the obstacle, and is the characteristic dimension of the obstacle (typically its diameter) or a characteristic length scale in the flow (like boundary layer thickness ...
The characteristic length depends on the geometry. For a circular pipe the characteristic length would be the diameter. For non circular ducts, the characteristic length would be: L=4A/p where A is the cross-sectional area of the duct, P would be the wetted perimeter. Note that for a circular pipe: L=4*(pi*D^2/4)/(pi*D) = D
Dimensionless numbers (or characteristic numbers) have an important role in analyzing the behavior of fluids and their flow as well as in other transport phenomena. [1] They include the Reynolds and the Mach numbers, which describe as ratios the relative magnitude of fluid and physical system characteristics, such as density, viscosity, speed of sound, and flow speed.
Mass per unit length kg⋅m −1: L −1 M: Luminous flux (or luminous power) F: Perceived power of a light source lumen (lm = cd⋅sr) J: Mach number (or mach) M: Ratio of flow velocity to the local speed of sound unitless: 1: Magnetic flux: Φ: Measure of magnetism, taking account of the strength and the extent of a magnetic field: weber (Wb ...
Length scales are usually the operative scale (or at least one of the scales) in dimensional analysis. For instance, in scattering theory, the most common quantity to calculate is a cross section which has units of length squared and is measured in barns. The cross section of a given process is usually the square of the length scale.
In physics, critical phenomena is the collective name associated with the physics of critical points.Most of them stem from the divergence of the correlation length, but also the dynamics slows down.
Physics is a branch of fundamental science (also called basic science). Physics is also called "the fundamental science" because all branches of natural science including chemistry, astronomy, geology, and biology are constrained by laws of physics. [58]