Centripetal and Centrifugal Forces

What is Centripetal Force?


When an object is force to change direction, something must be pulling it towards some center. If you have a weight connected to a string that you are swinging over your head, the force that is making the weight deviate from its straightline path is directed from the weight towards your hand along the string. This is called Centripetal Force and is the reason the weight is deviating from straightline to a curve path. It is real and straightforward in concept.

What is Centrifugal Force?

Objects are resistant to deviating from straightline motion.  If you are in a car and taking a turn, this resistance is very real. Nothing is pushing or pulling on you. Still you feel like something is pushing you toward the passenger side or into the door.

What you are feeling is not the effect of a force, but rather your body’s natural tendency to continue moving in a


straight line. For whatever reason, this inertial tendency is called Centrifugal Force. Its magnitude answers the question as to how hard the object is trying to maintain its straightline motion. It is a misleading name given to a consequence of inertial motion rather than an actual push or pull on an object.

How are Centripetal and Centrifugal Force Related?

The relationship between the two is straightforward. The two are equal in magnitude but opposite in direction. From this, it should be clearif Centrifugal Force was real, the object would move in a straightline because it would exactly balance out the Centripetal Force.


We therefore see that Centripetal Force is fundamental to describing the circle followed in curvilinear motion. But what is Centrifugal Force good for if it does not change how the object moves?

Why deal with with Centrifugal Force if it is not a real force?

If you are dealing with a point object connected to a string, Centrifugal Forces would be of minimum interest. But if you are talking about a driver in a car making a turn, this tendency towards straightline is very real. Anything not held in place will physically want to move in the direction of the straightline.  So Centrifugal Force becomes important for objects larger than a point that are free to move and follow their natural tendency.

For turning cyclists, the tendency of the cycle to continue in a straightline manifests itself in the cyclist’s body wanting to continue in a straightline along a different path than followed by the cycle. Because the tires are touching the road, this attempt to maintain straightline motion manifests itself in a torque that would tip the cyclist over. To counter this, the cyclist must lean in the opposite direction to that which their body wants to follow to create a counterbalancing torque.

Next Topics:   Centripetal Turning Forces




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