Escape velocity is the speed a moving object must have in order to escape from the gravitational pull exerted by another object. For example, the escape velocity from Earth’s surface is equal to about 6.8 miles per second (11 km/s). Anything that wants to escape Earth’s gravitational pull must go at least 6.8 miles per second (11 km/s), no matter what the thing is – a rocket ship or a baseball. The escape velocity of an object depends on how compact it is; that is, on the ratio of its mass to radius. A black hole is an object so compact that, within a certain distance of it, even the speed of light is not fast enough to escape.
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