It is sitting in the middle of a room with a smooth floor. You want to move it against the wall. You give it a push. It takes off, and before you know it, it slams into the wall. It is hard to stop it, because it has linear momentum .
Linear momentum is a measure of an object's translational motion.
The linear momentum p of an object is defined as the product of the object's mass m times its velocity v . Its direction is the direction of the velocity. If an object's velocity is changing, its linear momentum is changing. This is a more general statement of Newton's second law which also holds for objects whose mass is not constant. If an object receives an impulse its momentum changes.