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
Rigid body its position and orientation vary with time. In the kinematic sense, these changes are referred to as "translation" and "rotation", respectively. Indeed, the position of a rigid body can be viewed as a hypothetic translation and rotation (roto-translation) of the body starting from a hypothetic reference position (not necessarily coinciding with a position actually taken by the body during its motion). Velocity (also called linear velocity) and angular velocity are measured with respect to a frame of reference. The linear velocity of a rigid body is a vector quantity, equal to the time rate of change of its linear position.