Question

If a centrifugal force is fictional, what actually balances the the centripetal force of a body in circular motion

Answer 1

Hi! There's good description of that in the last response here:
http://www.physicsforums.com/showthread.php?t=3868

More good reading comes from Wikipedia!
https://en.wikipedia.org/wiki/Centrifugal_force

But the main point is, that centripetal force \(\sf\color{#DD2222}{ isn't}\) balanced. So there \(\sf\color{blue}{is}\) an acceleration - a.k.a. change in velocity.

In the picture, I mean the rotation to be in outerspace where gravity is not an issue. Now, the object is at the very top, moving counter-clockwise. You'll agree that the centripetal force is downward, and that the velocity is in the left direction. But there is an acceleration downward. And the object gains its downward velocity as its linear inertia is redirected. And as it revolves, it continues to be pulled towards the center. But it is traveling away from the center with its linear velocity. The centripetal force and acceleration is such that the object continues revolving.

These ideas aren't crystal clear to me either, but I hope this helps! We can continue to discuss it in this post if you want!

Answer 2

I appreciate your effort on explaining this but still the concept isnt striking me.

Answer 3

I'm sorry, @AravindG .

Did you check out the first link I posted?

It used a merry-go-round as an example. I'll use it too. But let me know if that example doesn't work well with you.

So, centrifugal force is made-up. It's like an explanation for a made-up problem, even. That made-up problem is seen when you are on a fast spinning merry-go-round, watching somebody on the edge. If you are not on the merry-go-round, you will not see this made-up problem intuitively.

So, some people are on a merry-go-round. It has been going for a little bit, and so everybody on the merry-go-round is up to speed.

Here's what's happening, as you will intuitively see from the outside. You look, and people are spinning around. Their velocities are changing, of course, since the direction of speed is changing. There must be some force to make these people in motion not travel in a straight line, says Newton's First Law! And the people must have a force in the direction of the acceleration, says Newton's Second Law! That force, the force pulling the people towards the center - whether it be friction on the ground or holding onto a pole - is called a centripetal force.

Here's the disagreement between the people on and off the merry-go-round. Keep in mind that that last paragraph was how the people off the merry-go-round saw it. The next paragraphs explains what the people on the merry-go-round were thinking, and the made-up problem that inspired a made-up force (centrifugal).

So, these people on the merry-go-round. They're not spinning, they say. And the people's tendencies to feel a force away from the center, that "couldn't" be because they're resisting the change in inertia!

Even though it is. Like, when you go forward in a car, you feel a force pushing you back. That's from your seat, doing the job of changing your momentum. On the merry-go-round, the centripetal force changes your momentum, but you must blame another force. After all, the person is at rest with the car just as much as the people are at rest with the merry-go-round.

The "problem" is, the merry-go-round people are feeling that real change of momentum, but it's due to the centripetal force pulling them in. They know about the centripetal force. They think it's what is holding them on (and it is). Then why aren't they moving, they ask. Well, it MUST be this change of momentum *cough cough cough* \(\color{red}{\text{I mean the "centrifugal force"}}\)\(\color{red}{\text{since we're not actually moving}}\)\(\color{red}{\text{and so our momentum is not changed}}\) *cough cough cough*. What were they thinking, change in momentum? They're not moving, right? Not according to them. As they see it, they are "still," and so there must be no net force. That's made-up: they do experience a centripetal force, but they are not still, and so they are not experiencing a counter-centripetal force called the "centrifugal force."

For the merry-go-rounders, it makes sense enough. For the people off to the side of the merry-go-round, they see it a different way.