The Traffic Accident Reconstruction Origin -ARnews-

Re: Codfficient of Friction of Grass

Bruno Schmidt ([email protected])
Fri, 9 Oct 1998 22:30:10 -0400 (EDT)

In response to the question about the units of the drag factor: It is a dimensionless quantity. It is the same no matter what units you use. In effect, it is the ratio of the acceleration due to braking divided by the acceleration of gravity. For instance, if the acceleration (actually, deceleration) is 16 ft/sec^2, since the acceleration of gravity is 32 ft/sec^2, then the drag factor is 0.5 (16 ft/sec^2/32 ft/sec^2). If we describe that very same acceleration in the metric system, we would have an acceleration of 4.9 m/sec^2. Since the acceleration of gravity can also be expressed as 9.8 m/sec^2, we still obtain a calculated drag factor of 0.5 when we divide a by g. The only thing that must be done here with respect to units is to use the same set of units for acceleration as you do for gravity when you perform the calculation to obtain the drag factor.

Bruno Schmidt
[email protected]

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