Inertia is the physical tendency of any mass to resist changes in motion. In auto racing, inertia makes the cars resist acceleration at the starting line. Once the car is moving, it will tend to keep moving in a straight line. Because race tracks are oval or circular, they have to be banked; this means that the track is higher at the outer edge of the curve than on the inside of the curve. This helps the driver to make the turn. Without banking, the car would be much more likely to go straight and run right off the racetrack. Drivers need to be vigilant in curves, as a slippery track can cause the car to lose adhesion with the track and slide sideways toward the outside of the curve.
Momentum is the product of mass and velocity, so the faster a car is going the more momentum it has. This means that a driver can let momentum carry the car at times, reserving some engine acceleration for maneuvering.
Understanding of these physics concepts has probably had the largest impact on the design of the driver safety systems. Airbags, netting, helmets, and multi-point body harnesses help to disperse sudden accelerations away from the driver's body. Avoiding sudden changes in acceleration is crucial for physical safety, because such forces can damage internal organs by shifting them suddenly within the body cavities.