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# Terminal velocity (potato-shaped obgject)

## Description

In fluid dynamics, drag (sometimes called air resistance, a type of friction, or fluid resistance, another type of friction or fluid friction) is a force acting opposite to the relative motion of any object moving with respect to a surrounding fluid. This can exist between two fluid layers (or surfaces) or a fluid and a solid surface. Unlike other resistive forces, such as dry friction, which are nearly independent of velocity, drag forces depend on velocity. Drag force is proportional to the velocity for a laminar flow and the squared velocity for a turbulent flow. Even though the ultimate cause of a drag is viscous friction, the turbulent drag is independent of viscosity.

Drag forces always decrease fluid velocity relative to the solid object in the fluid’s path.

The hyperbolic tangent has a limit value of one, for large time t. In other words, velocity asymptotically approaches a maximum value called the terminal velocity vt. For a potato-shaped object, terminal velocity is about given by this equation.

Related formulas

## Variables

 ut terminal velocity (m/s) g Standard gravity d average diameter of object (m) ρobj density of object (kg/m3) ρ density of the fluid through which the object is falling (kg/m3)