Velocity quantity, momentum, is a vector and defined by In special relativity, the dimensionless Lorentz factor appears frequently, and is given by where γ is the Lorentz factor and "c" is the speed of light. Escape velocity is the minimum speed a ballistic object needs to escape from a massive body such as Earth. It represents the kinetic energy that, when added to the object's gravitational potential energy, (which is always negative) is equal to zero. The general formula for the escape velocity of an object at a distance "r" from the center of a planet with mass "M" is where
Four-velocity the 3d position vector, written as a column vector The components of the velocity formula_2 (tangent to the curve) at any point on the world line are Each component is simply written In Einstein's theory of relativity, the path of an object moving relative to a particular frame of reference is defined by four coordinate functions "x"("τ"), where μ is a spacetime index which takes the value 0 for the timelike component, and 1, 2, 3 for the spacelike coordinates. The zeroth component is defined as the time coordinate multiplied by "c", Each function depends on one parameter "τ" called