Simulations / Physics

Crumple Zone Force Lab

A longer stopping distance means a longer stopping time and a smaller force. Change the car and its crumple zone, crash it into the wall, and see what the occupant feels.

Controls

How far the front of the car collapses while stopping.
A classroom design goal for occupant g-load, not a medical limit.
Ready Occupant g-load
Stopping time
milliseconds
Car deceleration
g (avg)
Force on car
kilonewtons (avg)
Occupant g-load
Model: constant deceleration from the impact speed to zero (a = v² / 2d), no rebound. The restrained occupant rides down over the crumple distance plus about 0.3 m (belt stretch and airbag) or 0.15 m (belt only); an unrestrained occupant stops in about 0.05 m against the interior.

Try this

  • Set crumple distance to 0.1 m, then 1.0 m at the same speed. How do force and time change?
  • Double the speed. By what factor does the force change? (Hint: v².)
  • Switch the occupant to unrestrained. Why is the g-load so much larger?

What to notice

  • Impulse (mΔv) depends only on mass and speed, but force = impulse ÷ time.
  • Doubling the stopping distance halves the force and doubles the stopping time.

Connect to the lab