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Centrifugal Force IS a “Real” Force

You’ve heard it somewhere on the internet, or perhaps a TV show – Centrifugal force is not a real force! It’s a pseudo-force! The only real force on a rotating object is the centripetal force! But that notion is misleading. In the past few months, I’ve heard far, far too many times people referring to centrifugal force as centripetal force. So, then – what’s what and when?

First, imagine a car cruising down the highway in a straight path. Moving objects want to keep moving in the same direction. So, if we came up on a curve and wanted the car to gradually turn left, we must push the car constantly towards its left. Picture below:

As can be seen on this expertly-drawn image, the centripetal force pulls the car towards the centre, changing its direction.

This push that turns the car into the curve is called centripetal force. “Centripetal force” is just a catch-all term for any force that causes an object to change direction. The friction between the car tyres and the asphalt, the tension of a string connected to a swinging ball, the force of gravity pulling the Moon towards the Earth. These are all fine examples of centripetal forces.

So what is centrifugal force, then? Centrifugal force is inertia in disguise. If you’ve ever filled a shopping cart to the brim, then you know that as the cart gets heavier, it gets more and more difficult to start, stop, and rotate. This difficulty to change direction is inertia.

If you are in a car and start turning left into a curve, the car turns just fine. You, however, are a fat, heavy glob of mass. A box of cheerios in the shopping cart. And since you aren’t bolted onto the automobile, you keep going straight as you were, resisting change in motion. This you experience as a force pushing you towards the right.

This (perfect frictionless) ball is a still object! But as the car moves, it appears as if there is a force acting on the ball pushing it around the car.

But really, there is only inertia, so what you are experiencing is a pseudo force. It seems like a force, but since it can disappear if you look at the world from the point of view of a passer-by rather than a passenger, it’s technically not a true force. But it does not make it not real.

Some other examples of pseudo forces are: the electric force, the magnetic force (both are only parts of the “true” electromagnetic force), the Coriolis force, and the force of gravity (technically a result of the curvature of spacetime, not a true force)

You may count them off as oversimplifications, but they are good enough that going for a technically more accurate overview would just not be worth the effort. All of these “fictitious” forces are useful. And really, this is all that matters.

So next time someone mixes up the centri-something forces, whack them over the head, and send them this post. You are the superior mind here. Now go and spread your newfound knowledge to the far corners of the pop-scientific territories!