The Speed from Length of Skid Marks calculator estimates the speed based on the length of skid marks and the friction coefficient.
INSTRUCTIONS: Choose units and enter the following:
Friction Coefficients
| 0.05 |
Very Slippery Conditions |
| 0.7 |
Normal Dry Conditions |
| 0.9 |
Ideal Breaking Conditions |
- (L) Length of Skid Marks
- (fc) Friction Coefficient
Speed from Length of Skid Marks (v): The calculator returns the speed in miles per hour. However this can be automatically converted to other velocity units (e.g. kilometers per hour) via the pull-down menu.
The Math / Science
The formula for the velocity based on the length of skid marks is:
`v = sqrt( 30*L*fc)`
where:
- v = initial velocity
- L = Length of Skid Marks
- fc = friction coefficient (0.05 for very slippery to 0.9 for ultimate breaking)
Braking Coefficient
The Braking Coefficient is a coefficient of kinetic friction. For accident reconstruction on dry surfaces, a value of 0.7 is often used. This is the default value in this calculator. A modern car with computerized anti-skid brakes may have a friction coefficient up to 0.9.
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References
- The Traffic Accident Investigation Manual, by J. Stannard Baker and Lynn B. Fricke