Centripetal force must be supplied by something or someone exerting the force on the object. In a rotating drum ride at a carnival you stand with your back on the drum. As the drum speeds up you can feel the force of the drum pushing on your back, toward the center of the circle. Often the floor drops down and only the force of friction between your back and the drum keeps you from dropping down with the floor.

When a car makes a turn what supplies the centripetal force on it? The road supplies this force. The road is in contact with the tires, and friction between the tire and road is necessary for the force of the road to be exerted on the car. If the road is covered with ice, the friction often isn’t large enough and the car goes straight, rather than along the curve. A racetrack is often banked so the tilt of the track can supply at least part of this inward force, reducing the need for friction.

If you’re sitting in the car there must be a sidewise force on you so that you stay with the car as it makes the turn. Usually the friction between you and the seat is sufficient, but sometimes you have to hold onto the door handle to exert more force.