mdot

Mdot, written as ṁ or described in text as "m-dot," is a symbol used in physics and engineering to denote a rate of change of mass with respect to time or, more commonly, a mass flow rate. The dot over the mass variable indicates a time derivative, so ṁ = dm/dt. In many applications, especially fluid mechanics and thermodynamics, ṁ represents the amount of mass crossing a boundary per unit time.

In fluid dynamics and process engineering, mass flow rate is a central quantity. For a steady, incompressible flow through a cross-sectional area A with density ρ and velocity v, ṁ = ρ A v. In a control-volume approach, mass balance is expressed as the inflow minus the outflow rates equaling the rate of accumulation: ∑ṁ_in − ∑ṁ_out = dM/dt. The units of ṁ are kilograms per second (kg/s). The term can also denote the time rate of change of the mass of a system, dM/dt, depending on context.

MDOT is also the abbreviation for the Mississippi Department of Transportation, a U.S. state agency responsible for the planning, construction, maintenance, and safety of roads, bridges, and other transportation infrastructure in Mississippi. The agency oversees state highway administration, asset management, and related transit and rail coordination, with duties spanning from daily maintenance to major capital projects.

Beyond these uses, mdot can appear in aerospace, chemical engineering, and software contexts where the concept of a mass flow rate or a time derivative of mass is relevant. Context usually clarifies whether mdot refers to a physical rate of mass flow, a derivative notation, or an organizational acronym.