Why Your Seatbelt Locks When You Yank It

The real science

Pull a seatbelt slowly and it glides out, but yank it and it locks right away. Inside the pillar, a spinning spool, a weighted arm and a tiny rolling ball all work together to stop the belt. Many cars also hide a small explosive charge that pulls the belt tight in a crash, but none of it helps unless you buckle up.

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