Motion Lab

Crumple Zone Lab

Time0.000 s
Car 1 speed16.0 m/s
How to use this simulation
  1. Open the Design tab. Pick a body style. Then set the crumple zone, the safety cell, the seat belt, and the airbag. The finished car remains visible while you adjust its design. Run a test to see how the crumple zone and restraints respond.
  2. Open the Crash test tab. Choose one car hitting a wall, or two cars hitting head-on. Set each speed. In a two-car crash you can also change car 2's mass.
  3. Press Play. The car drives up at normal speed. The crash itself plays back in slow motion, because the real crash lasts only about a tenth of a second.
  4. Watch the Time and Car 1 speed readouts. The thin strip under the scene shows the whole test track from above.
  5. Open the Results tab. The summary shows how much the car crushed, the biggest forces, and the dummy's chance of survival. Every run is added to the trial log so you can compare designs.
  6. Switch to Graph to see how displacement, velocity, deceleration, or force changed during the crash. Use the Table tab for exact numbers. Copy data lets you paste them into a spreadsheet.
  7. Press Reset to start over. Change one setting at a time. That way you know which change made the difference.
Why crumple zones save lives

A moving car has momentum. Momentum is mass times velocity. To stop the car, a force must act on it for some time. This push over time is called impulse.

F × Δt = m × Δv

The change in velocity (Δv) is set by the crash. So the only way to make the force smaller is to make the stop take longer.

A crumple zone is the front part of the car. It is built to fold up on purpose. While it crushes, the car keeps slowing down a little longer and over a longer distance. That lowers the force.

The safety cell is the strong cage around the people. It should not crush. If the crumple zone is too stiff, too short, or used up, the crash energy pushes into the safety cell instead.

The seat belt and airbag do the same job for the person. They stretch and squash so the body slows down over a longer distance. Without them, the dummy keeps moving until it hits the steering wheel. That stop is very short, so the force is huge.

Key words

Deceleration: how fast something slows down, in m/s². Doctors often compare it to gravity: 9.8 m/s² is 1 g.

Rigidity: how much force (in kilonewtons, kN) a part can hold before it starts to bend or crush. 1 kN = 1,000 N.

Stiffness: how much force it takes to stretch something by one meter. A stiff belt grabs hard. A soft belt stretches more.

Displacement: how far something moved from where it started.

Crash test dummy: a human-shaped model full of sensors. The black-and-yellow circles are targets that cameras track.

About the model

Each crumple zone crushes at a steady force equal to its rigidity. When it is fully crushed, the safety cell starts to crush at its own rigidity. In a two-car crash, the weaker structure crushes first.

The dummy has a mass of 75 kg. The belt acts like a spring. The airbag pushes back with a steady force. The steering wheel is 0.45 m in front of the dummy's chest and is very stiff. The head swings about 1.6 times farther than the chest, so without an airbag the head can hit the wheel even when the belt holds the chest.

Car 2 always has a 70 cm crumple zone (1,000 kN) and a 2,500 kN safety cell. The survival chance is a simple estimate based on the dummy's peak deceleration and safety cell damage. It is not real medical data.