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Grades K–2 · Materials & Matter

How can the foam inside a helmet soften a bump?

Inside many bicycle helmets is a thick layer of firm foam. It is not just a soft cushion for comfort. It has many tiny spaces that can be crushed during a hard bump.

W008 visual explanationCrushing foam spreads out a stop; Before a hard impact; Foam compressed; load; The crushed structure absorbs energy by changing shape.Crushing foam spreads out a stopBefore a hard impactFoam compressedloadThe crushed structure absorbs energy by changing shape.

In the diagramCrushing foam spreads out a stopBefore a hard impactFoam compressedloadThe crushed structure absorbs energy by changing shape.

An enlarged section compares uncrushed foam with crushed foam. The foam changes shape while the head slows down.

As the foam crushes, it changes shape while the head slows down. The stop is spread over more distance than it would be against a hard surface alone. Some of the energy goes into changing the foam.

The outer shell and straps help the helmet work as a whole. The foam cannot stop every injury, and crushed foam may not spring back ready for another bump. Its changing shape is part of the protection.

About this explanation

Starting knowledge: Compare a shape before and after it has been squashed.

Sources

  • American Academy of Pediatrics — Bike Helmets for Kids: Parent FAQs
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