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 a gravitational field without further propulsion.
For a spherically-symmetric body, escape velocity is calculated by the formula

where

*G*is the universal gravitational constant (G=6.67×10^{−11}m^{3}kg^{−1}s^{−2}), M the mass of the planet, star or other body, and r the distance from the center of gravity.
In this equation atmospheric friction (air drag) 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 walking 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 (assuming a non-rotating planet and ignoring atmospheric friction).
Source: Wikipedia

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