escape velocity

escape velocity the velocity a body must be given in order to escape the gravitational hold of some other larger body, e.g., the earth, moon, or sun. A body given less than the escape velocity will fall back toward the surface of the larger body; a body given a velocity equal to or greater than the escape velocity will still be attracted by the larger body, but this force will not be sufficient to cause it to return. Escape velocity depends on the mass of the larger body and the distance of the smaller body from its center, being proportional to the square root of the ratio of these two quantities. The velocity of escape from the earth at its surface is about 7 mi (11.3 km) per sec, or 25,000 mi per hr; from the moon's surface it is 1.5 mi (2.4 km) per sec; and for a body at the earth's distance from the sun to escape from the sun's gravitation, the velocity must be 26 mi (41 km) per sec.

escape velocity The minimum velocity required to escape from a gravitational field. The escaping object can be anything from a gas molecule to a spacecraft. A body's escape velocity is given by √(2GM/R), where G is the gravitational constant, M is the mass of the body, and R is the distance of the escaping object from the body's centre. An object moving at less than escape velocity enters an elliptical orbit; at exactly escape velocity it follows a parabolic trajectory; and if the object exceeds the escape velocity it moves away on a hyperbolic trajectory.