1. skid marks
February 11, 2014
Objective: police investigate skid marks
Is the pavement wet or slippery?
Investigators account for this by actually doing a pavement test at the scene.
What are the condition of tires?
Again, investigators account for this and adjust calculations.
Is there an incline to the pavement up or down?
If so, this must be recorded and the calculation must be adjusted.
Did the car impact some other car or object while skidding?
If so, a modified formula must be used.
Jan 30­6:29 PM
HW worksheets
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2. skid marks
February 11, 2014
D = k●V2 where D is the stopping distance in feet, V is the speed in miles per hour, and k is a constant that
depends on the frictional force of the pavement on the wheels of that particular vehicle. To accurately use this
formula, one must:
Experimentally determine the constant k for the particular vehicle in question driven on the same pavement, in
the same driving conditions. Drive at a known speed V. Brake suddenly. Measure the skid mark D. Use this
data to solve for k.
Driving at 30 mph the skid mark was 33.3 feet.
Jan 30­6:59 PM
HW worksheets
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3. skid marks
February 11, 2014
Now, figure the braking distance needed if you are
traveling at 35 mph.
55 mph
70 mph
Jan 30­7:01 PM
HW worksheets
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4. skid marks
February 11, 2014
http://www.youtube.com/watch?v=d8nPlBKiaUM&feature=related
Jan 30­6:41 PM
HW worksheets
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5. skid marks
February 11, 2014
In a different experiment it is found that a car going 40
mph left skid marks of 36 feet.
Find the distance needed to stop if you are traveling
45 mph
60 mph
Jan 30­7:02 PM
HW worksheets
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6. skid marks
February 11, 2014
Feb 11­11:19 AM
HW worksheets
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