An investigation related to the optimal speed of motion of a car (in sunny and rainy days, summer and winter) and of a submarine apparatus

摘要

The dependence of the minimal amount of energy (and thus of fuel) needed for a given journey (where the engine is never switched off),W_(min), with the density of the air, ρ, is estimated, for high velocities, asW_(min) ～ ρ~(1/3). Rainy conditions are especially interesting. The modelling uses the concept of average speed of the vehicle, allowing one to think about motion with constant speed. Different kinds of resistive force, appropriate also for motion in liquid, i.e. for submarine apparatuses, are considered. The discussion seems to be methodologically and motivationally appropriate for the classroom.