Bike Helmet
Bike Helmet
How does a bike helmet help reduce the impact of a crash?
Using equations if possible, thanks. I know that it spreads the force across a larger area of your head, but what about absorbing?
A helmet reduces the impact of a crash using two methods: distributing the force over a large area and slowing down the impact.
Using the basic equation of force, Force = mass * acceleration, we can look at how these two methods reduce impact.
Force can be measured simply as total force (e.g. 100 Newtons) or quantified by force over area (e.g. Newtons per square centimeter). As a bicycle helmet spreads the force for one point to a larger area, the force/area measure is decreased. This reduces the force applied to a single area, however, the overall force applied is still the same.
Acceleration is the other part of the equation that a helmet works to minimize. Acceleration is often measured as length over time-squared (e.g. meters/second-squared). Upon impact, the helmet is designed to crush, and this process of crushing extends the amount of time involved for the head to come to a stop (or before it bounces). This increases the time value in the measure, and since the time measure is a squared value, the effects of increasing the time involved has a big impact on reducing the overall acceleration and subsequent force.
To represent the two methods used by bicycle helmets to reduce impact, it is better to rewrite the original equation of Force = mass * acceleration as force/area = mass * (distance/time^2). Now you easily see where the added area for absorbing impact, and the increased time for the impact have big impacts on the trauma experienced by the head. The mass is slightly increased by the helmet, but nowhere near makes up for the distribution of force and slower acceleration (deceleration).
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