The escape velocity is the minimum velocity that a less massive object, such as a rocket, runaway star, or rogue planet, must have in order to escape completely from the gravitational influence of another, more massive body, such as a planet or a star, without being given any extra impetus. It can be calculated by taking the square root of (2Gm/r) where r is the distance from the center of the gravitating body of mass m, and G is the gravitational constant. This is equal, but in the opposite direction to the velocity it would have acquired if it had been accelerated from rest, starting an infinite distance away. The escape velocity can also be thought of as the velocity an object needs in order to attain a parabolic orbit – the lowest-energy open orbit. For an object leaving Earth's surface this is 11.2 km/s about 7 miles/s). An escape orbit is any orbit whose apoapsis lies at infinity. This includes parabolic orbits and hyperbolic orbits. If the body's velocity is less than the escape velocity, it is said to be gravitationally bound.
Related categories• CLASSICAL MECHANICS
• CELESTIAL MECHANICS
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