The Crumple Zone — Crushing Metal to Save Passengers
A crash-test car drives into a concrete barrier with a yellow dummy at the wheel, held by a three-point seat belt. Four sliders set the mass of the car (800–2500 kg), its speed at impact (20–100 km/h), the length of its crumple zone — the part of the front built to fold — from an almost rigid 0.10 m to 0.80 m, and the mass of the dummy (50–100 kg). The scene opens paused just before the impact. Press play and the crash runs once, filmed as if by a high-speed camera 40 times slower than real life, until the car and the dummy are at rest; drag the timeline to look at any moment of it, and move a slider to see the same moment of a different crash. Watch the blue front fold like an accordion against the barrier while the cabin stays intact, the belt holding the dummy as its upper body pitches forward, the pink arrow of the force on the dummy, and the force–time graph growing beside it.
इस सिमुलेशन का उपयोग कैसे करें
- Mass of the car M — 800 to 2500 kg, with 1200 kg marked. A heavier car brings more momentum and more kinetic energy to the barrier, but it stops in the same time, so the force on the dummy does not change.
- Speed at impact v — 20 to 100 km/h, with 50 km/h marked; the readout gives it in m/s as well.
- Crumple zone length L — from 0.10 m (an almost rigid front) to 0.80 m, with 0.60 m marked: how far the front can fold before the cabin.
- Mass of the dummy m — 50 to 100 kg, with 70 kg marked.
- Play/pause, back to the start, a timeline you can drag to any moment, and ½×, ¼×, ⅛× slow motion, on top of the scene's own slow motion (the crash 40× slower than real life, the roll back 10×).
- Drag anywhere on the scene to look around.
क्या देखें
- With the default 0.60 m the car stops in 86 ms and the dummy feels an average of 11.3 kN (16 g); slide to 0.10 m and it stops in 14 ms with 67.6 kN (99 g) — six times the force for the same stop.
- The floor scale under the front wheel reads the crush as it happens: the cabin keeps moving for 0.60 m after the bumper touches the barrier, and an amber mark holds the deepest point when the car springs back.
- Drag the timeline slowly through the impact: the belt keeps the dummy's hips on the seat, its upper body pitches forward a little, and the force–time graph is drawn up to the moment you are looking at.
- A rigid front throws the car back at 4.2 m/s (e = 0.30); at 0.60 m it leaves at 1.5 m/s and at 0.80 m at only 0.4 m/s. The energy bar shows where the 116 kJ went: 114.6 kJ into bent metal at 0.60 m, but 10.4 kJ left as the bounce at 0.10 m.
- Change the mass of the car: the force on the dummy stays the same. Raise the speed from 50 to 100 km/h: the force grows four times, from 11.3 to 45.1 kN. Change the mass of the dummy: the force follows it, while the deceleration stays at 16 g.
- On the force–time graph the area of each pulse is the dummy's change of momentum: the tall, narrow pulse of the rigid front even has a little more area, because that car also bounces back harder.
इसके पीछे की भौतिकी
Whatever its design, the car must lose all of its speed: 13.9 m/s at 50 km/h. In this model the front crushes at a constant force, so the car slows uniformly over the crumple length L and comes to rest after t = 2L/v: 86 ms for L = 0.60 m, 14 ms for 0.10 m. The squashed metal then springs back a little and pushes the car off the barrier at e × v, with the coefficient of restitution e falling from 0.30 for the rigid front to 0.03 at 0.80 m; after that the car is braked to rest. The car's momentum changes by Δp = m v (1 + e), and the average force is F = Δp/Δt. The belted dummy slows down with the car, so the force on it is its own mass times the same deceleration: 70 kg × 15.4 m/s ÷ 0.096 s = 11.3 kN (16 g) with a 0.60 m crumple zone, against 67.6 kN (99 g) with 0.10 m. That force does not depend on the mass of the car at all; it grows with the square of the speed and in proportion to the occupant's mass. Of the 116 kJ of kinetic energy (½ × 1200 × 13.9²) only the fraction e² comes back as the bounce; the rest — 114.6 kJ at 0.60 m — becomes internal energy of the bent metal through permanent deformation, vibration and heating, with a little sound. Real crash pulses are not flat: the model uses their average. It also assumes that the belt holds the hips to the seat and lets the upper body lean only as far as the strap pays out.