# Escape velocity

From Glossary of Meteorology

## escape velocity

(

*Or*escape speed.) The minimum speed that an object directed radially outward from an astronomical body must have in order to escape its gravitational attraction.The escape velocity for an object at a distance where

*R*from the center of a spherically symmetric body is*g*is the corresponding acceleration due to gravity. For*R*equal to the radius of the earth and*g*its surface acceleration due to gravity, the escape velocity is about 11 200 m s^{-1}. The earth retains its atmosphere only because this escape velocity is appreciably larger than the mean speed of air molecules.