## 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.

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## escape velocity

escape velocity Minimum velocity required to free a body from the gravitational field of a celestial body or stellar system. Escape velocities are: for the Earth, 11.2km/sec (7mi/s); and for the Moon, 2.4km/sec (1.5mi/s). They can be calculated from the formula: v = (2G M/R)1/2 where G is the gravitational constant, M the mass of the planet or system, and R the distance of the rocket from the centre of mass of the system.

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## escape velocity

escape velocity The velocity required for atoms or molecules at high altitude to escape from a planet's gravitational field. For example:

Planet

Escape velocity (km/s)

Earth

11.2

Moon

2.4

Mercury

4.3

Venus

10.3

Mars

5.0

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## escape velocity

es·cape ve·loc·i·ty • n. the lowest velocity that a body must have in order to escape the gravitational attraction of a particular planet or other object.