Should A Helmet Break On Impact?

In a crash, a helmet can save your life. But how exactly do they work?


Humans have made helmets for hundreds of years. The Greeks, Romans, Celts, and Vikings all used helmets to ride into battle. We apparently used helmets for multiple different reasons. Feathers and crests showed which army the wearer belonged to. Visors protected the eyes of jousters from enemy lances. It seems that for thousands of years, we’ve known how important and how fragile human heads and brains are!

Welsh leader
An ancient seal depicting a Welsh leader. The soldier and his horse are each wearing a helmet! Credit; Wikipedia/Hogyncymru

All helmets are used to protect against a sudden change in motion. Anything that’s moving, whether it’s a pen rolling off a table or an asteroid speeding through space, has energy . It’s impossible to make new energy. A lightbulb switching on uses electrical energy, but that energy came from a turbine: movement turned into electricity. The same lightbulb becomes hot after being switched on for a few hours: electricity turned into heat. Energy changes form all the time, and some forms are useful and some aren’t. Any moving object has kinetic energy .


When a moving object suddenly comes to a stop, all the kinetic energy has to go somewhere. This can happen if a brick suddenly falls from a construction site onto a worker standing below, or a cyclist is thrown from a bicycle. This energy can be harmful to the body and cause injuries. Helmets change the way kinetic energy affects our bodies, and turns the energy into multiple harmless forms.

How do helmets work?

If you’ve ever played with a rubber ball in a small room, you might know how difficult it is to stop its motion. Certain materials lose very little energy upon impact. A rubber ball keeps bouncing, and it takes many impacts for it to slow down. All the kinetic energy stays inside the ball. During a sudden impact or crash, we don’t want the energy to stay in our body. We want to turn it into other forms and stop the motion. A helmet helps us do that.


A helmet is made up of many layers. The foam layers inside the helmet are designed to “crush” upon impact. The sudden impact pushes all the air in the foam out, packing it tightly. Doing this takes a surprising amount of energy away from the head, protecting it.


If a cyclist were moving along a road and experienced a sudden crash without a helmet, their head would meet the road very quickly. Helmets slow down this impact. As the foam crushes and the outer shell experiences a hit, there’s a delay before the motion and kinetic energy reaches the head. The speed of the impact and the energy the head experiences are reduced.


The outer shell of the helmet is also the first defense against the force of an impact. It needs to disperse this force, quickly. This is why the material often breaks, cracks, or even shatters. Ultimately, this is a good thing! All the energy that’s used up in breaking the helmet isn’t experienced by the user’s head. The more energy the helmet uses up, the better. This is why it’s a good thing if the helmet breaks—it’s dispersing energy well!

Different helmets are used for different purposes, Credit: Wikimedia/Brandenads

It’s important to use the right helmet. Construction helmets, motorcycle helmets, and bicycle helmets are all designed for different impacts from different directions. Regardless of the purpose, a helmet that has been dropped or been in an accident should never be reused. It can only absorb the energy once! A helmet that’s done its job well and protected your head can be safely retired.


Flesch Kincaid Grade Level: 67.8

Flesch Kincaid Reading Ease: 6.8


Energy: The ability to do work, whether through moving, heat, light, or another property


Kinetic energy: The energy possessed by a moving object


  • Yamini Srikanth
    : Author
    Yamini's (he/they) interests lie in environmental education, science communication and trying to build a better world. When not languishing in front of his laptop, they can be found outside, poking at any insect, bird or plant. They love making science accessible, especially to those who aren't encouraged to pursue it. Yamini hopes that the young women who read Smore love learning from their articles and get just a little bit more excited about science!

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