Impulse (physics)

In classical mechanics, impulse (symbolized by J or Imp) is the change in momentum of an object. It is most often used to describe forces which act over short time periods, specifically in the case of impacts and collisions, for which it gets its namesake. Impulse is a vector quantity, meaning it has both a magnitude, which describes the amount by which the momentum changed, and a direction, which describes the direction in which the momentum changed. For a force acting over a short time, the impulse is often idealized so that the change in momentum produced by the force is modelled as happening instantaneously. This sort of change is a step change, and is not physically possible. However, this is a useful model for computing the effects of ideal collisions (such as in videogame physics engines). Additionally, in rocketry, the term "total impulse" is commonly used and is considered synonymous with the term "impulse". Impulse has the same units and dimensions (LMT−1) as momentum. The SI unit of impulse is the newton-second (N⋅s), and the dimensionally equivalent unit of momentum is the kilogram-metre per second (kg⋅m/s). The corresponding English engineering unit is the pound-second (lbf⋅s), and in the British Gravitational System, the unit is the slug-foot per second (slug⋅ft/s).