Momentum
A fundamental vector quantity equal to the product of an object's mass and its velocity, representing its quantity of motion.
Governing formula
p = m v
SI unit
kg·m/s
In depth
Linear momentum is conserved in all isolated systems where net external force is zero. In relativistic mechanics, momentum scales with the Lorentz factor: p = γ m v.
Examples in the real world
A heavy freight train moving at low speed possesses immense momentum, making it difficult to stop compared to a lightweight car at the same speed.