1. Tire Impressions and Accidents

2. Tire impression can tell a lot about accidents involving cars
Speed of driver
Which driver is at fault

3. Skid marks Produced by friction between tires and road
Friction always opposes direction of motion
Depends on type of surface and how hard they are pressed together

4. Speed Determined by length of skid marks and drag factor
Drag factor = friction force / weight
Determined by drag sled or accelerator attached to car
Higher the value more friction involved with surface

5. Common drag factors

6. Calculating the Speed of car
Determines the minimum speed that could cause the skid marks for any vehicle
Speed = √(30*distance*drag factor)
S = √(30*d*f)