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The Misconception Behind Centrifugal Force

Updated on December 5, 2016

Centrifugal forces play a major role in our every day lives. They're what make us jerk to the right when the bus driver takes a tight left turn and what dry our clothes in the washing machine when we're late for work. There's only one problem: they don't exist.

Centrifugal comes from the latin roots centrum (center) and fugere (to flee), and is defined as the apparent force that acts outward on a body moving around a center. The term was coined in 1684 by Sir Isaac Newton in his De Motu Corporum, and several years later, the German philosopher Gottfriied Leibniz defined the centrifugal force as being a real outward force induced by the rotation of the body on which it acts.

While there is no such thing as centrifugal force, there is a centripetal force. The centripetal force, defined as the inward force acting on a rotating body to keep it in a circular path, acts in the opposite direction of the fictitious centrifugal force, and is calculated by multiplying the object's mass by its velocity squared and dividing by the radius of the circle through which it is rotating.

Now, it makes perfect sense why Newton and Leibniz believed in some outward force. Let's say you attached a ball to a string and began swinging it in a perfect circle over your head (as shown in the diagram below). Once you let go, the ball would continue to travel in a straight line tangent to the circle at the point where you released it. Thus, there must be some force pulling that ball away from its circular path of motion correct? Well, no, because centrifugal force is not in itself a force, but a lack of a force. According to Newton's First Law of Motion, an object at rest will remain at rest, and an object in motion will stay in motion unless acted on by some unbalanced force. In our case, the reason the ball continues in a tangential trajectory is that the centripetal force has been removed, and there are no more external forces to keep it from traveling in a straight line. We call this inertia.



Now let us consider another scenario. Pretend we begin spinning another ball attached to a string, but this time it is out in front of us and parallel to our body. We then release the ball as it reaches the top of its swing (highest point in its circular path). According to Newton's first law, a body should move in the direction of an unbalanced force, and by releasing the string, we are eliminating the centripetal force. Disregarding gravity, the only force acting on the ball would then be our supposed centrifugal force, and the ball would take a sharp turn upwards. How many times have you seen a ball do that? I challenge you to try it at home...

The reason centrifugal force has been so debatable is that, unlike normal forces, it is dependent on one's frame of reference. If I were observing a child on a carousel, I would report no outward force acting on that child, just an inward one. However, if I were to personally stand on the carousel, I would feel a force acting on me, trying to pull me out of the circle. This is why today, physicists refer to it as a pseudo force: an apparent force acting on all bodies observed in a non-intertial frame of reference.

Even if centrifugal forces technically don't exist, they still have important implications. When engineers design curved roads, they have to calculate the centripetal force and frictional forces acting on the car to counteract the "centrifugal" force that threatens to pull them off the road. In space, NASA engineers have to make sure the "centrifugal" force would counteract Earth's gravitational pull so that the International Space Station could remain in orbit. Centrifuges incorporate high-speed rotations and centrifugal forces to separate liquids of different densities. Even many amusement park rides, such as the Gravitron, utilize these forces in their design. They don't have to exist to be important.

So, yes, you've been lied to. Physics teachers hardly ever teach this the right way (I know mine didn't), and it irritates me so much to know that students are being taught a misconception. So here's the gist: there is no such thing as a centrifugal force, but there is a centripetal force, and the physical applications we can derive from it are critical in many of the technologies we use today.


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      Frank Smith 

      13 months ago

      A rotating mass "EXERTS" a centrifugal force as a reaction to the centripetal force.

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