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Overview
Momentum is a vector quantity that measures an object's quantity of motion. In classical mechanics, linear momentum depends on mass and velocity.
Mass and Velocity
Momentum increases when mass increases or when velocity increases. A massive object moving slowly and a small object moving quickly can both have large momentum.
Momentum as a Vector
Momentum points in the same direction as velocity. Direction matters, so momenta in opposite directions can cancel in a total system calculation.
Momentum and Force
A net force acting over time changes momentum. This connects momentum to Newton's laws and to impulse.
Impulse
Impulse is force acting over a time interval, and it equals change in momentum. It explains why both force size and contact time matter.
Conservation of Momentum
In an isolated system with no external net force, total momentum is conserved. Objects inside the system can exchange momentum with one another.
Momentum in Collisions
Momentum is conserved in elastic and inelastic collisions when external net force is negligible.
Common Mistakes
A common mistake is treating momentum as a scalar. Another is assuming momentum conservation applies to a single object rather than the total isolated system.
Applications
Momentum appears in collisions, sports, vehicle crashes, rockets, recoil, explosions, particle physics, and fluid motion.
Why This Matters in Physics
Momentum connects force, time, motion, interactions, and conservation laws.