Escape velocity
In physics,
escape velocity is the speed at which the kinetic energy plus the gravitational potential energy of an object is zero. It is the speed needed to "break free" from the gravitational attraction of a massive body, without further propulsion. For a spherically symmetric body, the escape velocity at a given distance is calculated by the formula where
G is the universal gravitational constant,
M the mass of the planet, star or other body, and
r the distance from the center of gravity. In this equation atmospheric friction is not taken into account. A rocket moving out of a gravity well does not actually need to attain escape velocity to do so, but could achieve the same result at any speed with a suitable mode of propulsion and sufficient fuel. Escape velocity only applies to ballistic trajectories. The term
escape velocity is actually a misnomer, and it is often more accurately referred to as
escape speed since the necessary speed is a scalar quantity which is independent of direction.