With contragravity, of course, terms like "escape-velocity" and "mass-ratio" were of purely antiquarian interest.
|escape velocity |
The velocity needed for a celestial body to overcome the gravitational pull of another, larger body and not fall back to that body's surface. Escape velocity is determined by the mass of the larger body and by the distance of the smaller body from the larger one's center. Depending on its initial trajectory, a smaller body traveling at the escape velocity will either enter a periodic orbit around the larger body or recede from the surface of the larger body indefinitely. The escape velocity at the Earth's surface is about 11.2 kilometers per second (25,000 miles per hour); the escape velocity on the Moon's surface is 2.4 kilometers per second (5,300 miles per hour). The escape velocity within the event horizon of a black hole is higher than the speed of light; since nothing can exceed the speed of light, nothing—even light—can escape from within the event horizon of a black hole.
The speed an object must reach to escape the pull of gravitation exerted by another object.