Centrifugal Force vs. Centripetal Force

If you frequently talk about bodies in motion, you might have heard of the terms ‘centrifugal force’ and ‘centripetal force.’ However, the odds are that you’ve heard people using these terms incorrectly.

In fact, quite a lot of people believe these two forces to be one and the same. But it couldn’t be further from the truth. For starters, they work in opposite directions. Also, one of them is actually not a real force. Let’s take a closer look.

Centrifugal Force

If you’ve had an interesting physics teacher in school, you probably saw him spin a bucket with water around. You might also remember that the water didn’t spill even when the bucket was upside down. The reason for that was the centrifugal force. The name centrifugal comes from Latin words ‘centri,’ and ‘fugere’ and roughly translates to “fleeing from the center.”

To put it simply, it is a force that is “pulling” objects away when they are spinning quickly. You can actually feel this force at work almost every day. Namely, you can feel it every time you are in a car that takes a sharp turn. You can feel that your body wants to continue going straight instead of turning. And that is exactly what the centrifugal force is about.

After all, it is not actually a force. It is simply your inertia pushing you forward. That inertia is what drives the string to tighten when you start spinning a stone on it. That inertia is what lets you throw things really far by spinning them. And, lastly, that inertia is what drains the water out of your laundry when the washing machine starts using the centrifuge.

But, after all, that is said and done, you can’t experience the centrifugal force without the centripetal force.

Centripetal Force

The centripetal force is the centrifugal force’s counterpart. While centrifugal force acts on objects that are in a rotating frame of reference, pushing them outwards, the centripetal force is bringing them back in. That is why the second part of the word is ‘petal,’ coming from Latin ‘petere’ which means ‘to seek.’ While the centripetal force doesn’t come from the fact the object is spinning (unlike the centrifugal force) it affects the way said objects behave.

In fact, without the centripetal force, the spinning motion would be all but impossible. Allow us to explain with a simple example. Let’s say you tie a rock to a string and start spinning it. The inertia from the movement will act as the centrifugal force. As such, it will work to get the rock to fly away in a straight line. However, the string you are using will act as the centripetal force. It will hold the rock down, preventing it from flying away.

How Do They Connect?

To put it simply, we can’t experience one of these forces without the other.

If you take the rock and a string experiment to a grand scale, you can do the same with satellites. Namely, the gravity of our planet is pulling the satellites down towards us. But, in a rotating frame of reference, their inertia acts as a centrifugal force and keeps them going forward. It is the balance between these two forces that keep satellites from flying away or crashing into the planet.

The reason most people confuse the two forces has mostly to do with different viewpoints and frames of reference. If you are standing outside a rotating system, you can only see the centripetal force. You can see the body trying to fly straight and the centripetal force constraining it to a circular path.

On the other hand, if you are inside of the rotating system, it seems to be the opposite. The only force you can feel is the force trying to pull you away from the center. In essence, you are feeling the effect of the centrifugal force. That is why we can utilize centrifuge for a number of devices. For example, we commonly use this principle in laboratory centrifuges. Those devices can separate red blood cells from your blood.

In the end, one can also say that these two forces are the exact same force. But they work in opposite directions due to the fact that we experience them from different frames of reference.

But, if you want to achieve circular movement, you have to balance the two forces. If either of the two ends up lacking, the circular movement will end. If you don’t have enough inertia (or centrifugal force), the object will go back to the center. Conversely, if you lack centripetal force, the object will simply fly away in a straight line. After all, that is exactly what happens when you let go of something you were spinning around yourself.

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