Final answer:
Gravity in NASCAR racing increases traction by enhancing the contact force between the car and the track. It does not increase the mass of the car nor is it typically responsible for increasing car speed on flat tracks, but does play a role in how cars handle turns due to increased downforce.
Step-by-step explanation:
The force of gravity in NASCAR racing is advantageous because it increases the contact force with the track, thus creating more traction. When a NASCAR vehicle accelerates around a curve, even if its speed is constant, it is still accelerating due to the change in direction, and this acceleration is provided by the centripetal force, which in this context is a result of the friction between the tires and the track. The gravitational force, acting downwards, increases the normal force between the car and the track, enhancing this frictional force and thus the available traction.
Additionally, racetracks are typically banked to maximize this effect, allowing cars to maintain higher speeds through turns without relying solely on tire friction. However, the misconception in option (c) should be corrected as gravity does not increase the mass of the car; mass is an intrinsic property of an object and is not affected by gravitational force. And while gravity does assist in pulling a car downhill, increasing its speed (option b), this is not generally a factor in NASCAR as tracks are generally relatively flat and do not have significant elevation changes where gravity would play a direct role in increasing car speed.