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In physics and engineering, the time constant, usually denoted by the Greek letter τ (tau), is the parameter characterizing the response to a step input of a first-order, linear time-invariant (LTI) system. [1] [note 1] The time constant is the main characteristic unit of a first-order LTI system. It gives speed of the response.
For example, the atomic mass constant is exactly known when expressed using the dalton (its value is exactly 1 Da), but the kilogram is not exactly known when using these units, the opposite of when expressing the same quantities using the kilogram.
In the International System of Units (SI), the unit of time is the second (symbol: s). It has been defined since 1967 as "the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom", and is an SI base unit. [12]
As a dimensional quantity, the value of the gravitational constant and its possible variation will depend on the choice of units; in Planck units, for example, its value is fixed at G = 1 by definition. A meaningful test on the time-variation of G would require comparison with a non-gravitational force to obtain a dimensionless quantity, e.g ...
the equation indicates that the decay constant λ has units of t −1, and can thus also be represented as 1/ τ, where τ is a characteristic time of the process called the time constant. In a radioactive decay process, this time constant is also the mean lifetime for decaying atoms.
G-factor (physics) Gas constant; Gaussian gravitational constant; H. ... Time constant; Time-variation of fundamental constants; W. Weinberg angle This page was ...
A mathematical constant is a key number whose value is fixed by an unambiguous definition, often referred to by a symbol (e.g., an alphabet letter), or by mathematicians' names to facilitate using it across multiple mathematical problems. [1] For example, the constant π may be defined as the ratio of the length of a circle's circumference to ...
Absolute, true and mathematical time, of itself, and from its own nature flows equably without regard to anything external, and by another name is called duration: relative, apparent and common time, is some sensible and external (whether accurate or unequable) measure of duration by the means of motion, which is commonly used instead of true ...