A fender bender is a momentum accounting problem. Momentum — mass times velocity — cannot be created or destroyed in a collision, only transferred between the vehicles. That single conservation law lets crash investigators work backward: from the crumpled final positions, they reconstruct how fast each car was moving before impact. Insurance adjusters, auto safety engineers, and physics students all balance the same books.

In plain words, the momentum before equals the momentum after: m₁v₁ + m₂v₂ = m₁v₁′ + m₂v₂′. For each vehicle, its momentum is just its mass times its velocity — and that product is exactly what this calculator computes.

Picture a 3,000-pound sedan rear-ending a 4,000-pound SUV at a stoplight. Type the sedan's mass in the Variable A box and its speed in the Variable B box; the Result box gives its momentum. Repeat for the SUV, then compare the totals before and after — conservation says they must match, and any mismatch points to energy lost crumpling metal. That lost energy is precisely what modern crumple zones are designed to absorb instead of your body.

With the pre-filled defaults — Variable A 10, Variable B 5 — the Collision Calculator returns Result 50.0000. Change any input and those results update instantly, so you can see exactly how each number you enter moves the answer.