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	Forensics Case 13 Life in the Fast Lane: Using skid marks to determine vehicle speed

Activity Overview

Students determine the coefficient of friction between a vehicle and a road surface. They use the length of the skidding distance to determine the speed of a vehicle before its brakes were applied. Students convert between SI units and Imperial units and rearrange equations to solve for different variables.

Before the Activity

Use TI Connect™ to download: Vernier EasyData™ application

Connect the Dual-Range Force Sensor to Vernier EasyLink™ interface

Plug EasyLink into the USB port of the calculator

Set up the EasyData App to collect one sample every 0.02 seconds for 2 seconds

See the attached PDF file for detailed instructions for this activity

Print pages 114 - 118 from the attached PDF file for the class

Print sample data and student work pages

Activity Downloads:

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During the Activity

Distribute the pages to the class.

Follow the Activity procedures:
Part I: Determine the Coefficient of Friction

Model a vehicle to skid: Use a tight rubber band between the axles or stuff tissue in the wheel wells of a toy car to prevent the wheels from rotating

Zero the force sensor with nothing attached to it

Connect the hook on the sensor to the string attached to the vehicle

Using a steady force, pull on the force sensor to move the vehicle across a smooth, flat surface at a constant speed.

Collect data when the vehicle starts moving

View the graph and ensure that the vehicle is moving at a constant speed

Calculate the average force used to pull the vehicle

Use the force sensor to weigh the vehicle

Calculate the coefficient of friction for the vehicle and the surface it skidded on

Part II: Find Speed from Skidding Distance

Use chalk or tape to mark a starting line

With the wheels locked, push the vehicle and let it skid from the starting line

Measure the skidding distance

Repeat the activity

Calculate the speed that the vehicle was traveling when it crossed the starting line and began to skid

Use the length of the skid to find the speed of the car and determine which suspect's car was involved in the car chase

After the Activity

Students analyze the data collected and answer the Case analysis questions.

Review student results:

As a class, discuss questions that appeared to be more challenging

Re-teach concepts as necessary

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Subject Area:
Math : Algebra I : Data Analysis
Math : Algebra II : Data Analysis
Science : Physics : Kinematics
Science : Forensics : Data Analysis
Math : Statistics : Data Analysis

Author:
Texas Instruments