em.... G-force datangnya dari momentum dan inersia kereta. Semasa kereta membrek, G force akan menampung berat kereta, sekiranya kereta + pemandu ringan... G-Force ni la yang angkat kereta hang kedepan....
You ask about G-force, but you are in fact only attempting to calculatedeceleration. G (32 ft/s/s) is a measure of acceleration, not force(F=ma).
Surviving is a function of force, not acceleration. If you fall into ahard chair from a standing position, you experience about 10G's onimpact. But the force is spread over a half square meter of the tissueof your ass, which absorbs much of the force before passing it on tobones, etc. But 10g's spread over 1 square cm will pass right throughyou.
Car impact analysis is massively complicated. Watch that car crashvideo and notice the front left wheel collapse and bits of metal flyingoff the car. Those breakage events represent a force applied to thatpart of the car that exceeds that part's mechanical limits. Atbreakage, the force isn't transferred through the part to the rest ofthe car, it's absorbed entirely by the part which snaps. Commensuratewith that breakage is a reduction in acceleration.
People die in car crashes not because the driver hits a wall or a treeor another car. They die (usually) because the cabin of their own carhits them (usu. wheel or dash, and the impact area is about 2cm^2). Thepurpose of crumple zones and material choices in the body are designedto model a shock absorber between the point of impact and the positionof the driver. In other words, to ensure that the driver's accelerationcurve is different than the car's and to ensure that the cabin is able to traverse a slightly longer distance than the front of a car.Even an additional meter of travel makes a huge difference. Moredistance = lower acceleration = lower force. An inverse relationshipbetween the car surviving and the driver surviving.
Cars in the fifties weighed about as much as they do now, believe it ornot. The reason they look like tanks is because they were built likethat. Cars were built to survive impacts. So the steel was think andheavy, and everything was bolted together as strongly as possible. Theresult of this is that cars survived crashes, but drivers didn't.
Car mfgs had to design in breakage points. Lift the hood of your carand look at the underside. You'll see the steel rolled into a boxaround the perimeter of the hood that gives the hood it's rigidity. Butlook closely and you'll see notches taken out of it. That notch isprecisely where the hood is going to bend on impact. They know exactlyhow much force that notch can take before the hood bends around it.
As the body crumples, acceleration is lost, and force is absorbed bythe car body and not the driver. Thus, the proper way to model acollision is at minimum as a three-body problem: the wall, the cabin,the driver. You can see that as you add collapsible steering columnsand breakaway dashes, axles, engine parts, etc, the number of bodies inthe collision becomes huge.
Also, note that he doesn't actually hit a wall, he hits a tire wall andappears to extend into it. The tire wall also absorbs the force ofimpact both through friction (car slides between tires and tires slideon road) and as less-than-ideal springs (the tires squish). Thiscombines to help reduce the a in F=ma. This is also why abutments on UShighway exit ramps are often filled with sand or water.
Furthermore, as dario noted, the deceleration is very non-linear andnon-uniform, especially with the car falling apart as it heads towardsthe wall. Secondly, think of the length of an F1 car. If the front ofthe car crumpled by one meter on impact, it means the driver moved anadditional meter after the front of the car stopped.
So assuming the front of the car crumples by 1m, that actually gives you a distance of 3.44 meters that the driver travels,not 2.44m. This drops the G's to about 66.6 from 92, almost 30%. That's30% less force he feels. Factor in the skidding, the smashed tire, thedirt, etc, and it's very easy to see how his speed was far below 150mphwhen he hit the wall. That means that the force he felt was well withinthe range of minimal bruising. You can see he walked away from thiscrash.
With all that said, you can now appreciate why the single mostimportant safety feature in a car, and especially an F1 car, are theseat belts. Without seat belts, the deceleration of the car and thehuman are independent. The car decelerates first on impact, which meansthe driver starts moving in the cabin at a speed equal to thedifference between the speed of the car at the moment of impact and amoment later. Even if the car was going 60 and a moment later was going40, the driver is moving 20mph.
The seat belt links the human's acceleration curve to the midpoint ofthe car body, allowing the entire front half of the car to be destroyedin the process of absorbing the impact force and slowing the midpointdown before any part of the car touches you.
Despite the restrictive aerodynamic rules for 2009, teams have adoptedvarious approaches to the front ends of their cars. The major designdifficulties to overcome have been the standardised central section ofthe front wing and the wing's lower position, which together riskmaking the nose very pitch sensitive under braking. To avoid this onthe R29, Renault have adopted a stepped main profile, which helpscreate a kind of Venturi effect under the nosecone. The nose's bulgingshape is designed to speed up airflow, reducing pressure and boostingdownforce, whilst the two central pillars boast backward extensionsthat continue along the underside of the nose, acting like turningvanes. The wing features a single flap and wide endplates which divertair away from the front tyres and reduce drag.
PS : Semua team duk kaji benda ni..... kita tengok team yang mana paling hebat.....
Formula One will undergo a series of changes for the 2009 season,withthe cars launched to date showing a radically different look tothoseraced in 2008.
Aswell as the visual appearance of themachines, 2009 will see the returnof slick tyres, the introduction ofKERS, and changes in engine regulations that will leave teams needing to make each engine last longer during the year.
This video sees Sebastian Vettel talk through the main changes, with some help from the video wizards at Red Bull...
[ Last edited by ShadowChaser at 12-2-2009 09:59 AM ]
Post time 4-2-2009 11:54 AM
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