Impact Force Calculator
Calculate impact force from mass, velocity, and stopping time or distance.
Find peak force during collisions, falls, and sudden stops in newtons and pounds.
Impact force is the average force experienced during a collision or sudden stop. It depends on how fast the object was moving, how massive it is, and — most critically — how long the stopping takes.
Method 1: From impulse and time F = m x Δv / t
Where Δv is the change in velocity (usually from v to 0 for a full stop) and t is the duration of the collision. A car airbag extends the stopping time from milliseconds to about 50ms, reducing peak force on the occupant by roughly 3-5x compared to hitting the steering wheel directly.
Method 2: From kinetic energy and stopping distance F = m x v² / (2d)
This is the work-energy approach: the kinetic energy (½mv²) must be absorbed by the force over the stopping distance d.
Both methods give the average force. Real impacts involve rapidly changing force — a spike at initial contact followed by decay. The average is used because the peak is hard to measure and varies by material.
Practical reference points:
- A 70 kg person falling 1 meter and stopping over 0.01 seconds (hard floor): ~12,000 N (about 1.2 tons-force)
- Same fall, stopping over 0.1 seconds (soft mat): ~1,200 N — ten times lower
- A car at 60 mph stopping in 0.15 seconds in a crash: forces exceed 30g on occupants
- A smartphone dropped 1 meter: peak forces can exceed 100g at the corner
This is why padding, crumple zones, helmets, and airbags all work by the same mechanism: increasing stopping time or distance to reduce peak force.