Final answer:
The physics concept of centripetal force is used to make a car go in a circle by relying on the friction force between the car's tires and the road.
Step-by-step explanation:
In order to make a car go in a circle, the physics concept of centripetal force comes into play. Centripetal force is the force that acts towards the center of the circular path, keeping an object moving in a curved path.
To achieve this in a car, the force of friction between the car's tires and the road provides the necessary centripetal force. The friction force causes the car to turn in a circular path as it moves forward.
Therefore, the string used to make a car go in a circle is not a string at all. Instead, it is the friction force between the car's tires and the road that enables the car to maintain its circular motion.