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Physics estimate: the fall height that produces the same impact speed (v² ÷ 2g). Stories use about 10 feet each. Real crash injuries depend on the vehicle, angle, restraints and much more.
Why buckling up works
In a crash, the car stops but your body keeps going at the car’s speed until something stops it. A seat belt stops you with the car, over a slightly longer time, across the strong bones of the hips and chest. Without it, you are stopped by the dashboard, the windshield, another passenger or the ground. Car seats do the same for children, sized to their bodies.
Fun facts (and not-so-fun facts)
- 91.3% of people in the US wore seat belts.NHTSA, 2025
- Car seats reduce the risk of fatal injury in a crash by 71% for infants and 54% for toddlers.NHTSA
- 48% of passenger vehicle occupants killed in crashes were not buckled up: 9,758 people.NHTSA, 2024
- Nearly half of all car seats are installed incorrectly.NHTSA
Classroom activity: the egg drop
Have teams build a “car” for a raw egg (a small box or cart) with and without a “seat belt” made of tape or rubber bands, then roll it down a ramp into a wall. Measure the ramp height, then use the calculator to talk about the same physics at real speeds. Use a tarp; eggs win sometimes.
Questions people ask us
Is a 30 mph crash really like falling off a building?
In terms of speed at impact, yes. Hitting something solid at 30 mph means stopping from the same speed you would reach after falling about 30 feet, roughly 3 stories. A seat belt and airbags spread that stop over more time and more of your body.
Why does speed matter so much?
The equivalent fall grows with the square of speed. At 60 mph it is about 120 feet, four times the 30 mph figure, not twice.
