## Wednesday, January 14, 2009

### Analysis - Car Hits Boy On A Bike

In our last post, we looked at a quote from a Spanish traffic organization and proved that a cyclist cannot go airborne and land on the thirteenth floor of a building after a car collision.

Why I did a trajectory analysis is due to the fact that a cyclist-car collision is very different from a pedestrian-car collision as far as impact points on the car are concerned. Studies have found that not only do cyclists hit the car structure under different angles, but they also hit higher than pedestrians. In contract to pedestrians who mostly hit the bonnet and bumper of a car, the main impact location for cyclists was found to be the windshield. So in the analysis, I assumed that the windshield will elastically collide with the cyclist, and the cyclist will bounce off it into the air with a high velocity like a firecracker on an independence day celebratory occasion. In reality we know this won't happen, because the head will absorb the impact, bones could break, the car may dent, glass could shatter, and friction will ensure that there is a limit to how high the cyclist flies.

In order to avoid a disconnect between topics, I have attached additional collision literature today for a reading session over coffee. This paper is an interesting one because its an analysis of a real accident where a car collided with a little 7 year old boy on a bicycle in one of the most dangerous cities in the US - Camden, New Jersey . It was authored by Dr. Micheal J. Ruiz, professor of Physics at the University of North Carolina at Ashville, USA and his ultimate aim is to present easy techniques to estimate the initial velocity of the striking vehicle.

The paper presents the analysis by looking at the accident using two ways : 1) Simple momentum conservation using elastic collision with assumed vault distance and co-efficient of restitution close to one, 2) Collins speed formula - a slightly advanced analysis using quadratic kinematic equations and accounting for the co-efficient of friction on the road.

The paper concludes that the initial velocity of the car at impact was around 11-12mph. Yet, such a low speed appears to have been enough to send the young boy flying 10 metres or 32 feet away from the impact point, eventually fracturing the rear section of his skull.

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#### 1 comment:

Phil said...

I wonder if the same people who cry out against the use of helmets allow their kids to go without one. For me, thats the ultimate test of hypocrisy.