vT

vT is a symbol that appears in several technical contexts and does not have a single universal meaning. Its interpretation depends on the field and the surrounding equations.

In physics and engineering, v_t (or occasionally v_T) is commonly used to denote terminal velocity—the constant speed at which drag force balances gravity for a body falling through a fluid. Terminal velocity depends on factors such as mass, cross-sectional area, drag coefficient, fluid density, and gravity, and it is a central concept in aerodynamics, ballistics, and atmospheric studies.

In electronics and semiconductor physics, V_T or v_T is used for the thermal voltage. This is defined as V_T = k_B T / q, where k_B is Boltzmann’s constant, T is absolute temperature, and q is the elementary charge. The thermal voltage sets the energy scale in Boltzmann statistics and appears in current–voltage relationships for diodes and transistors. At room temperature, about 300 K, V_T is approximately 25.7 millivolts.

Other uses exist in different disciplines, often as a variable name or shorthand in specific models and equations. Because vT is not standardized across fields, it is essential to consult the source material for the precise definition in any given context.