It is very common to see people referring to centrifugal force when talking about circular motion. Imagine, for example, a sphere attached to a string and in uniform circular motion, under the centripetal force (F c ) acting on the string. Many people have the habit of assuming the existence of another force, called centrifugal force (F cf), which acts on the sphere. According to these people, this force would be balancing the other force that acts on the string. This assumption is wrong, because the centrifugal force does not exist, because if that happened the resultant force on the sphere would be zero and therefore it could not be describing uniform circular motion. If so, the motion of the sphere would be straight and uniform according to Newton’s first law, the law of inertia.
This misinterpretation is probably due to the fact that people believe that the sphere is in equilibrium. However, for an observer who is on Earth (referential) it is not in a state of equilibrium, because the sphere has centripetal acceleration and, therefore, there is a non-zero net force acting on it. Another factor that suggests this erroneous interpretation is that if the string holding the sphere breaks, the sphere will begin to move outwards, in the radial direction, this displacement being attributed to the action of the centrifugal force. This concept is wrong because if the string breaks, the sphere, by inertia, starts to move in the direction of velocity at that instant, that is, tangent to the circular trajectory that the sphere was describing, proving that there is no force acting.