Calculate the average force in a collision from the mass, impact speed and the stopping distance or stopping time.
Last updated: November 8, 2026
Work-energy and impulse methods
The average force in a collision depends on how short a distance or time the object's energy or momentum is brought to zero in: • From stopping distance: F = m × v² ÷ (2 × d) • From stopping time: F = m × v ÷ t Example: a 1,000 kg car hitting a wall at 15 m/s (about 34 mph) and crumpling 0.5 m feels an average force of 1,000 × 15² ÷ (2 × 0.5) = 225,000 N. That is about 23 times its weight (23 g). The result is an average; the peak force in a real crash is higher. Airbags and crumple zones lower the force by lengthening the stopping distance.
Common questions about impact force
With a stopping distance, F = m v² ÷ (2d). With a stopping time, F = m v ÷ t.
Other tools you may find useful
In kilograms.
15 m/s ≈ 34 mph.
How far it travels while stopping.