The Traffic Accident Reconstruction Origin -ARnews-

Re: Seven Drag Factor Questions

Ed Phillips (edphill@aol.com)
Fri, 28 Feb 1997 17:52:04 -0500 (EST)

Larry,

I also noticed that your skid tests are (-) 23 percent and (-) 16 percent of what your vehcile testing was. The length of the skid mark does not encompass the length of the slowing. There is a period of spin down where the tires are being braked and rolling less and less fast until they reach incipient lock-up and lock-up. This distance that leaves no tire mark can effect your friction computations. A bumper gun device can account for the overall distance of deceleration as opposed to the length of wheel lock-up and skidding. The tested values from the vehicle test will therefore be higher because the distance in the skid is shorter than the actual distance of slowing. And that 's' is in the denominator of the friction equation (v^2/2gs). The larger the denominator, the smaller your resultant value. E.g., 1/1 vs 1/1000.

Ed
Ed Phillips
edphill@aol.com

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3 Mar 2004 06:58:24 -0700 (MST)