Inverse second

The inverse second, written s⁻¹, is the reciprocal of the second. It measures quantities with dimensions of inverse time, including frequency and rates.

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Second: The SI base unit of time, defined by fixing the caesium-133 hyperfine transition frequency. The inverse second is defined by taking the reciprocal of this unit of time.
Frequency: The number of repeating events or cycles occurring per unit time. Cycles per second are measured in hertz, equivalent in dimension to s⁻¹.
Revolutions per minute: A unit of rotational frequency equal to the number of turns completed in one minute. It expresses cycles per time in a named unit rather than as inverse seconds.
Rate: A quantity describing change in another quantity per unit time or per unit of another variable. Dividing an event count or probability change by time produces inverse-time units.
Reciprocal: The reciprocal of a nonzero number is one divided by that number. An inverse second is the reciprocal of one second.
Radioactive decay: The spontaneous transformation of unstable atomic nuclei into other nuclei or particles. A decay constant expressed in s⁻¹ gives the probability rate of decay per unit time.
Radian per second: A unit commonly used for angular velocity, expressing angular displacement per unit time. It is often written for angular rates where s⁻¹ alone would omit the quantity's interpretation.
Exponential decay: A process in which a quantity decreases at a rate proportional to its current value. The exponent combines a decay constant in s⁻¹ with time in seconds to form a dimensionless value.
SI base unit: A unit designated as a foundational unit in the International System of Units. The second is an SI base unit, so its inverse provides a coherent derived unit.
First-order reaction: A chemical reaction whose rate is proportional to the concentration of one reactant. Its rate constant has units of inverse time, including s⁻¹.