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Line the students in groups of two or three on the sidewalk at 10 m intervals (using a 10 m piece of string). Have one student stand up and work the stopwatch, and the other student sit down (or stand back) and record the data. The teacher will stand at one end of the line, 10 m from the first set of students, holding the flag. When a car passes the teacher, the flag is dropped and all the students start their stopwatches. As that car passes each set of students, they should stop their stopwatches and record the time in their notebook along with a description of the car. Since the groups are so far apart, a set of hand signals should be developed for the students to use to tell everyone if a mistake was made and the data set should be erased.
Back in the classroom, a graph with time on the x-axis and and distance on the y-axis should be constructed by the students for each car. This may either be done by hand, or by using a software program like Clarisworks (see below). A straight line can then be drawn that best represents the points on the graph AND passes through the origin of the graph (this will make the slope calculation easier). Then a point on the line can be picked, and the y-value of the point divided by its x-value will be the speed of the car! This can be converted to miles per hour by dividing by 0.44704.
To further this investigation, different groups of students can analyze different cars and share their findings. The average speed of the cars can then be calculated, as can the range of speeds. The students should then be able to make conclusions based on their findings. An extension of this activity could then be to write a letter to the editor of the local paper and report the student findings!
You may want your students to use a spreadsheet template to enter their data. If you click on the icon below, a spreadsheet file icon will appear on your computer's desktop. To open the file, double click its icon. In the spreadsheet, the computer automatically plots time as a factor of distance. The E column of the spreadsheet is deliberately left blank to allow students to enter the formula for calculating miles per hour (see above). The charts in the spreadsheet will "come alive" as students enter data. It can be interesting for students just to change the data figures just to watch the changes in the chart data.
