# 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 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 m3 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 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 (assuming a non-rotating planet and ignoring atmospheric friction).

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### Famous quotes containing the word escape:

Self-love is often rather arrogant than blind; it does not hide our faults from ourselves, but persuades us that they escape the notice of others.
Samuel Johnson (1709–1784)