Escape velocity

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Escape velocity or escape speed is the speed an object must have in order to completely escape the gravitational pull of a more massive body such as a star, planet, or moon. The speed is generally calculated by neglecting atmospheric drag or other forces, and with the assumption that no additional force is applied to propel the object other than whatever force(s) gave it its initial speed. In other words, the first object's motion is affected only by the gravitational force from the massive body. Such an object would continue to move farther and farther from the massive body, rather than orbiting the massive body or crashing to the surface.

Typically, the escape velocity or speed is taken at the surface of the massive body, though it can also be defined for various altitudes above the massive body's surface. The initial direction of the object does not affect the value of the escape speed, provided its trajectory does not intersect with massive body's surface (for example, the object cannot be launched downward). An object launched with a speed greater than the escape speed will escape the massive body's gravitation regardless of whether it is launched directly upward, or at an upward angle from the surface. As such, the term speed is more appropriate to use than velocity, which would apply when the direction of motion is or must be specified. However, the term escape velocity is a commonly used term.