Jumat, 09 Agustus 2013

How does a bike helmet help reduce the impact of a crash?

bicycle helmets for big heads on ... Speed 24w 2013 Jump Bike | DMR | Wheelies Direct Bike Replacement
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Grant


Using equations if possible, thanks. I know that it spreads the force across a larger area of your head, but what about absorbing?


Answer
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).

When riding my bicycle, should I stop at all stop signs and red lights?




vargasdfw


I just bought a bicycle. When I am going in neighborhood streets I feel silly stoping at the stop signs, and on some other streets even stoping at a red light. If a policeman sees me, not stopping, will I get a ticket (????). Please explain how it works.


Answer
A bicycle is considered as a Vehicle, that's the first thing you should know.

In most jurisdictions, bicycles must have functioning front and rear lights when ridden after dark. As some generator or dynamo-driven lamps only operate while moving, rear reflectors are frequently also mandatory. Since a moving bicycle makes little noise, some countries insist that bicycles have a warning bell for use when approaching pedestrians, equestrians and other bicyclists.

You' are expected to obey the rules of the road w/e mode of transportation you are using. Think about it, if you don't stop at the stop sign, you're risking yourself! You never know you might get into an accident. The largest cause of serious and fatal injuries to cyclists is collision with motor vehicles.

Yes, if a policeman saw you, he can and will give you a ticket for beating a red light/not stopping at stop signs. A "failure to stop, Stop sign" citation was worth $122.97 for a cyclist violation and $158.97 for a motorist bust.

One good answer to dealing with a ticket would be to work it off at Bike Traffic School (if there's one close to you)

How to avoid tickets:

Signal your intent â Boost your predictability and get in the habit of signaling your intended path, using hand gestures that let everyone know what you're doing. A lot of right-of-way confusion and resentment can be resolved easily with a few clear hand signals, just point out your path if there are other people around to whom that would be useful information. You'll be surprised at how smoothly things go.

Don't be a right-of-way thief â Rolling s l o o o o o w l y across a stop line at an empty intersection is one thing, but barging in front of someone (car, bike, pedestrian, bus) is bound to draw anger at least and maybe a ticket.

Watch for cops, and don't do anything stupid in front of them â Really, use your head. Traffic officers tell us that they don't try to hide, they sit right out in plain view with their big shiny motorcycles and bright "white dot" helmets and the black and white cars. It's incredible how many cyclists (and motorists and pedestrians) will pull a brazenly illegal maneuver right in front of a cop. If you can't bring yourself to play nice when the police are obviously watching, maybe you need that ticket to clue in.

Nothing in the law says that a "complete stop" requires a cyclist to take his/her foot off the pedal and make contact with the ground. CVC 21201 does say that a bicycle must be small enough for the rider to stop, support with one foot on the ground, and restart safely, but whether or not a complete stop is made ultimately hinges on a police officer's discretion.

Bicycle riders under age 18 must wear a helmet under California law(I don't know what's yours in your state). Riders 18 and older can decide for themselves. If you do choose to wear a helmet, make sure it's properly sized and fitted. Headlights are required for night riding, as are reflectors: red in the back and yellow/white on sides and pedals (reflective whitewalls count).

Maybe you can learn something from this link just disregard the city name I'm pretty sure you don't even live in bay area >.<

http://www.youtube.com/watch?v=o7M-_ueoU2E&eurl=http://www.sfbike.org/?bikelaw_sfpd_video




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