A customer called recently looking for ideas on aerodynamic drag experiments. This inspired us to do a little research with toy cars on the roof of a car.
We mounted two toy carts: one streamlined, and one not as aerodynamic. They were connected so that our Dual-Range Force Sensor would measure the drag force on them as we drove them along through the air. Our team of investigators included a driver, a computer operator, and someone to yell out the speedometer readings.
We collected Events with Entry data using Logger Pro. We tried to find a level stretch of road, and we used a new feature of Logger Pro 3.5 that allowed us to do a 10-second sample of the average force for each reading.
There are several sources of error, such as road vibration, changes in the road grade, wind, and the driver sometimes not holding the speed constant for the 10 seconds. Even so, the data pretty nicely show that the drag force is proportional to the square of the velocity, and that the more aerodynamic car had less drag.
Two cars connected to Dual-Range Force Sensors to measure drag force
Drag force vs speed for two cars