Originally Posted by
yugo campione
A question still remains unanswered in what you put forth. Maybe you can add insight, how do the number of people killed, or with severe head trauma, compare with say, auto accidents, or shower falls, or just walking and tripping? All those, as well as countless other activities, I'm sure offer significant potential for head injuries, yet it is not common at all for anyone to wear a helmet during those activities. Do you wear a helmet when you drive? Why not? I am willing to wager that there are far more head traumas due to auto accidents than bicycling every year. Am I wrong? If I am not wrong, why do you, specifically, not wear a helmet everytime you get behind the wheel of your car?
There can be a quite lengthy answer to that, especially since you're asking several different questions. But to concentrate on the main point: I am not wearing a helmet while driving because our cars already have a "helmet" incorporated into them. It's threefold: the outer metal casing that crumbles during an accident, a seatbelt, and an airbag. I am much safer inside the car even at high speeds than on a bike on lower speeds (compared to each medium). NASCAR drivers do wear helmets. There are numerous additional variables. For example, when you're in the shower or doing other daily personal activities, you're mostly in control and your cerebellum is a pro at these movements. In contrast, when you're riding, you can be the best professional, but you do not have control on what other cyclists or drivers will do to you - more prone to accidents outside of your control.
Here is another report over the course of almost 10 years in NYC:
97% of cyclist who died were not wearing a helmet. I could cite so many additional papers where people actually did a study using the scientific method, but I have yet to see a single paper backing up the dangers of helmets.
I am surprised that there is so much controversy about this. The bottom line is that if a helmet can slow down your impact even by a few fractions of a second, you will definitely benefit. This is not a matter of opinion but physics. What is the purpose of helmets, airbags, vests, etc? All they're trying to do is spread the amount of applied force in time. F=ma=dp/dt. Delta p, or change in momentum, is also known as impulse. Therefore, F=I/dt.
Let's take a very rough example: cyclist weight = 70kg, speed=9 m/s. The impulse in an inelastic collision (full stop, no deformation) = 70*9=630 kg*m/s. To calculate the force, use F=630/dt and start plugging in some numbers for dt (change in time) to play around. If dt=0.150 s, which is how long a car crash can last, the force is 4200 N (newtons). To give you an idea, it takes 2200N to break the bones of your skull (assuming ~6 cm square area). Now lets slow down that time twice: dt=0.3 s. Then F=2100N. This is the proof that a helmet is going to help your skull because regardless of anything else, the helmet is always going to slow down the amount of time it takes for the impact to occur and hence dramatically decrease the force. This is what is meant by "cushioning" and the extra lining.