[Physics] If an object moving in a circle experiences centripetal force, then doesn’t it also experience centrifugal force, because of Newton’s third law

Question

When an object moves in a circle, there's an acceleration towards the center of the circle, the centripetal acceleration, which also gives us the centrifugal force (since $F = ma$ is the equation for a force and the acceleration of an object, therefore, is caused by a force). But according to newton's third law, for every action, there is an equal and opposite reaction, which would mean that because of the centripetal force there's an equal force outwards, which I would say is the centrifugal force. But this is obviously not true since that would mean that the net acceleration on the object moving in the circle would be 0. So my question is, what is actually this reaction force that's created by the centripetal force, and where does the centrifugal force come from? I do know that the centrifugal force can be viewed as an inertial force in a certian reference frame, but is there any way to describe it in another way? I can imagine that the centripetal force may come from friction with the road if you're in a car and if the reaction force is the force into the ground it makes sense, except for the centrifugal force.

Answer 1

This is a common misinterpretation of Newton's third law, often stated as "to every action, there's an equal and opposite reaction." As you surmise, "action" and "reaction" refer to forces. However, they refer to forces acting on different things. Otherwise, nothing could accelerate, ever: if every force were always canceled out by an equal and opposite force, no force could ever do anything. Instead, forces occur between objects--say car and road, to take your example. The road exerts an inward force on the car, which, you're right, is the centripetal force. The equal and opposite force is exerted by the car, on the road. The two forces are acting on different things, so they do not cancel. This second force (the force exerted by the car on the road) is sometimes referred to as the "reactive centrifugal force," which is confusing, because it's different from the more common meaning of centrifugal force.