Momentum
![](/Images/godic/202501/06/Billard3857.JPG")
![A Newton's cradle demonstrates conservation of momentum.](/Images/godic/202501/06/Newtons_cradle_animation_book_23857.gif")
![Newton's apple in Einstein's elevator. In person A's frame of reference, the apple has non-zero velocity and momentum. In the elevator's and person B's frames of reference, it has zero velocity and momentum.](/Images/godic/202501/06/Relativity_an_apple_in_a_lift.svg3857.png")
![Two-dimensional elastic collision. There is no motion perpendicular to the image, so only two components are needed to represent the velocities and momenta. The two blue vectors represent velocities after the collision and add vectorially to get the initial (red) velocity.](/Images/godic/202501/06/Elastischer_stoß_2D3857.gif")
In classical mechanics, linear momentum or translational momentum (pl. momenta; SI unit kg m/s, or equivalently, newton second) is the product of the mass and velocity of an object. For example, a heavy truck moving rapidly has a large momentum—it takes a large or prolonged force to get the truck up to this speed, and it takes a large or prolonged force to bring it to a stop afterwards. If the truck were lighter, or moving more slowly, then it would have less momentum.