Answer to Question #107745 in Physics for Avalon

Question

Using Newton's Laws, why do vehicles use more gasoline for city driving than for highway driving?

Answer 1

2^nd Newton's Law:

$$ma=F-F_f$$

$$F_f^{maintain\ speed}=\mu_kmg<F_f^{accelerate}=\mu_smg$$

The answer is that vehicles use more energy to accelerate than they do to maintain speed. In the city, vehicles make many stops and starts. Accelerating a vehicle from zero to even a slow speed like 35 or 40 mph several times takes quite a bit more energy than accelerating a vehicle to 70 mph and maintaining it. Using more energy means using more gasoline to generate it, which is why vehicles get fewer miles per gallon in urban driving than they do on interstates and highways.