Accident Reconstruction: Measuring Coefficient of Friction


Subject Area


Age or Grade

9th -12th Grade

Estimated Length

90 minutes

Prerequisite knowledge/skills

Newton's Second Law
Description of New Content

The students will learn one way of measuring the coefficient of frcition (in particular, as it is done by police in reconstructing accident scenes) and how the coefficient varies with the properties of the surfaces.


  1. For the students to understand the effect of varying surface conditions on coefficient of friction.
  2. To prepare students for an end-of-the-year accident reconstruction challenge by introducing them to one of the primary tools used by police in analyzing accident scenes.
Materials Needed

This lab utilizes a simple tool of accident reconstructionists to measure coefficient of friction between automobile tires and the road. Click here for instructions on how to build a drag sled.

  • Tire
  • Eye-hook
  • Empty toolbox
  • Sand
  • Spring scale

Lab Handout

Here are some pictures of Mr. Long's Advanced Physics class working on the lab.


If desired, you can challenge the students to take the lab one step further by having them compare different grades of tire. Do higher grade tires exhibit a larger coefficient of friction than other types? Do snow tires have a significantly improved coefficient of friction with an icy roadway? How do snow tires perform on a dry roadway? Are "all-weather" tires accurately named?

Of course, this lab can also be extended to other road surfaces.

Here are a couple of example problems to supplement the lab.

This lab was inspired by Crash! The Science of Automobiles, a text written by Professor John Kwasnnoski, certified accident reconstructionist. His text connects much of introductory high school physics (uniformly accelerated motion, friction, circular motion, etc.) with the real life challenge of reconstructing accident scenes.
Coefficient of Friction