2023 ASEE Annual Conference & Exposition

Due to the integrated sensors, smartphone owners carry not only handy communication tools but also fully-fledged data acquisition and measurement systems in miniature form in their pockets. The measured data can be transferred quickly and easily to laptops or desktop PCs, where they are then available for further processing. Consequently, smartphones can enrich physics and engineering education in many ways, as they enable low-threshold access to physical measurement methods.
In order to make use of this possibility, undergraduate student research projects with measuring tasks were initiated. One of them was the determination of the rolling and aerodynamic drag coefficients of model vehicles by using the accelerometers of their smartphones. The coastdown technique should be used, in which the vehicle is accelerated to a specified speed, shifted into neutral and allowed to decelerate freely. The time rate of change of its velocity is proportional to the total resistive force, which is assumed to consist of a speed-independent rolling resistance and an air resistance proportional to the square of the vehicle's speed.
A smartphone attached to the model vehicle provides the time-dependent acceleration data, which is usually noisy and needs to be smoothed. The vehicle velocity, on the other hand, can be obtained from the acceleration data by numerical integration. By plotting the vehicle acceleration on the abscissa and the velocity square on the ordinate in a coordinate system for the coasting process, a straight line can be fitted. From the slope of this straight line, the aerodynamic drag coefficient can be derived, and its intersection with the ordinate provides information on the rolling resistance coefficient.
Three teams of three or four students each worked simultaneously and competitively on that project. They independently conducted experiments and developed computer programs for the visualization of the data and evaluation of the measurements. In this paper, the theoretical background, the approach to the problem and the outcome of the undergraduate student projects are presented and discussed.