# Some Questions on Physics (Force) HELMETS

## Main Question or Discussion Point

1. Why is the force reduced for a helmet with a soft interior VS Hard interior?

2. What points would need to be considered during design and construction to ensure that the impact on the body is decreased? What criteria must be met?

3. Why should a helmet be replaced every 5 years regardless of wear and collision?

4. Once A helmet has been involved in a collision why should it be replaced?

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Drakkith
Staff Emeritus
1. Why is the force reduced for a helmet with a soft interior VS Hard interior?
Hard interiors transfer the energy of the collision very quickly and efficiently. If you apply a force, such as the force of your head impacting the concrete, over a short amount of time or distance then the acceleration (or deceleration) is higher than if you increase the time or distance the force is transfered. One of the main causes of injuries is very high acceleration of the body. This causes internal organs to impact the inside of the body with a large amount of force, injuring them. Also, soft interiors absorb energy better than hard ones, leaving less energy available to cause injury.

Note that just because one helmet feels softer inside doesn't mean it is actually better. A soft foam that absorbs almost no energy will be much worse than a firmer one that absorbs alot. Make sure any helmet you get is certified.

4. Once A helmet has been involved in a collision why should it be replaced?
Absolutely. Especially helmets like motorcycle helmets. They are designed so that on impact the helmet absorbs the energy, resulting in permanent damage to the helmet instead of your head. Even a small amount of damage to the helmet could be what causes permanent brain injury. Just because the helmet looks like it only has a few scratches doesn't mean the inside hasn't been damaged.

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3. Why should a helmet be replaced every 5 years regardless of wear and collision?
Probably because the materials used degrade over time and their properties will not be the same...instead of remaining spongie, they dry and become brittle or something.

Thanks guys i really needed that