# Momentum

## Momentum (Encyclopedia of Science)

The momentum of an object is defined as the mass of the object multiplied by the velocity of the object. Mathematically, that definition can be expressed as p = m · v, where p represents momentum, m represents mass, and v represents velocity.

In many instances, the mass of an object is measured in kilograms (kg) and the velocity in meters per second (m/s). In that case, momentum is measured in kilogram-meters per second (kg · m/s). Recall that velocity is a vector quantity. That is, the term velocity refers both to the speed with which an object is moving and to the direction in which it is moving. Since velocity is a vector quantity, then momentum must also be a vector quantity.

Conservation of momentum

Some of the most common situations involving momentum are those in which two moving objects collide with each other or in which a moving object collides with an object at rest. For example, what happens when two cars approach an intersection at the same time, do not stop, but collide with each other? In which direction will the cars be thrown, and how far will they travel after the collision?

The answer to that question can be obtained from the law of conservation of momentum, which says that the total momentum of a system before some given event must be the same as the total momentum of the system after the event. In...

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