Lab and Demo: Velocity on Our Streets
Demo: An introduction to the Lab Exercise “Traffic Cop”
(Straight-Line Motion)
Lane Matheson/Leonard Freise/Bruce Dillon
7/2/02
Equipment:
- Toy car (alternatives: marble, remote-controlled car or robot, student riding in a red wagon down a ramp)
- Masking tape
- Stopwatches
- Two poles with colored streamers
- Tape measure
- Board or other item to use as a ramp (unless object is powered)
Procedure:Select a location in your class room at least 2 meters long and without obstacles or bumps. Mark a starting point and an ending point for the path of a model car to be rolled down a ramp. See picture below. Set up the poles with streamers at these marks so that students can see them from a distance. Measure the distance between the marks and record. Students need to stand as far back from the set-up as possible to minimize parallax. Have the students practice using the stopwatches several times while rolling the car down the ramp and across the marked path. Ask the students to begin their stopwatches when the car front crosses the start and stop their watch when the car front passes the finish line. Record each student’s time on the board. Have each student calculate the average of all the measured times.
Discussion: We want to determine the average speed of the car between the start and finish lines. Average speed is calculated by dividing the change in distance traveled by the change in elapsed time. Thus, if the distance and time are known then we can determine the average speed with the formula:
After presenting the formula, have students calculate the average velocity of the car using the average time calculated earlier.
Questions for students:
- In what situations might you want to determine average speed?
- What are other measurement tools that could be used?
- Why did we calculate the average time for everyone’s measurements?
- What are common measurements for speed?
- What does the word “per” mean in the statement “miles per hour”? How can knowing what “per” means help you to remember the formula for average speed?
- Convert the average velocity we calculated into miles per hour. Write out the conversion factors needed, since you will need them later.