**In physics, the impulse of a force is the product of the average force multiplied by the time over which that force was applied.** Impulse is closely associated with the concept of momentum, as one can often be used to calculate the other.

In cases where the mass of the object in question remains constant, the impulse can also be equal to the momentum of that object. Momentum is found by taking the product of the mass and the velocity. The concepts of impulse and momentum are commonly related through collisions. The basic rationale is that a collision produces a change in momentum, which leads to the impulse of a force. When the mass is constant, impulse can be found through the following equation: mass x (final velocity) - mass x (initial velocity).

This change in linear momentum is commonly referred to as the impulse-momentum equation. Several variations of impulse exists. Impulse can also refer to a force that acts quickly, which is typically referred to as an impact. Specific impulse is a term used to measure the efficiency of jet and rocket engines. This item is measured in velocity units, and the force is given as a representation of the propellant used with respect to time.