The ease with which an object's motion can be influenced depends on its mass and velocity. It is not easy to either turn a huge, slow-moving truck or stop a comparatively lightweight racing car moving at a high speed exactly at the finish line. The mass in motion can be characterized by a physical quantity called linear momentum. The linear momentum of a body, represented as p, is the product of its mass, m, and velocity, v. The SI unit of momentum is kilogram meter per second. It is a vector quantity having the same direction as that of velocity. The greater the mass and velocity of the object, the greater will be its momentum, making it difficult to influence its motion.