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## #1 2018-11-22 14:23:48

CIV
Member
Registered: 2014-11-09
Posts: 74

### Physics: Help with understanding Centripetal and Centrifugal forces.

Oh my goodness... I've and have been told that centrifugal force is fictitious yet it's mentioned and used to make calculations as if it's real. I'm so confused!

Things I understand:
- Centripetal force is a center-seeking force.
- Centripetal force is the tension of something holding a mass to the center of a circular path. As the angular velocity of this mass increases, so does the centripetal force.
- Centripetal force is observed from a reference point that is not relative to the rotating mass or center of rotation.
- Centrifugal force is a center-fleeing force.
- Centrifugal force is observed from a reference point that's relative to the rotating mass.

Is centrifugal force the lack of centripetal force? What is the force pulling/ pushing a mass away from the center? Centripetal force is pulling/ pushing the mass to the center, what force is moving the mass away from center? It's said that centrifugal is fictitious so..... I don't get it.

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## #2 2018-11-22 14:53:07

CIV
Member
Registered: 2014-11-09
Posts: 74

### Re: Physics: Help with understanding Centripetal and Centrifugal forces.

Wait a second...... my book says that an example of a centrifugal force is the normal force preventing a mass from reaching the center of the earth. The ground exerts a normal force keeping you from sinking in to the earth. If I swing a yo-yo around in a circle over and over, the only thing between the yo-yo and the center is the string, but the string is whats exerting a centripetal force (tension) that's trying to pull the yo-yo to the center. There's a force moving the yo-yo away from the center, the centrifugal force, and because there's nothing between the yo-yo and the center to exert this force its therefore fictitious.

Am I right?

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## #3 2018-11-22 15:36:59

ganesh
Registered: 2005-06-28
Posts: 28,479

### Re: Physics: Help with understanding Centripetal and Centrifugal forces.

Hi CIV,

Welcome to the forum!

It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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## #4 2018-11-23 03:46:35

bob bundy
Registered: 2010-06-20
Posts: 8,541

### Re: Physics: Help with understanding Centripetal and Centrifugal forces.

Hi CIV,

I've managed to do A level maths and physics and then later teach it, without ever needing to refer to centrifugal force.  Why do we need something that's made up ?  Mathematicians would never consider something that's imaginary would they ?

According to Newton, an object such as your yo yo, will go in a straight line unless acted upon by an external force.  To make it go in a circle a centrally acting force is needed and that's what we call centripetal force.  We can feel the string tugging but that's just the tension in the string.

If you could cut the string whilst the yo yo is whizzing round, it would continue in a straight line, tangential to the circle. If you're sitting on the back seat of a car as it is driven round a sharp bend, there's nothing to stop you from carrying on in a straight line.  You might think you're being pushed sideways but actually you're going straight and the car (which can go in a circle due to friction between the tyres and the road) is curving towards you.  When you make contact with the side of the car, the car can exert a force on you, to make you go in a circle too.

The genius of Newton was he could see past the individual's self centred perspective and understand what is really going on. I regard avoiding the term centrifugal as part of my homage to the great man.

Bob

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob Bundy

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## #5 2018-11-23 18:57:41

CIV
Member
Registered: 2014-11-09
Posts: 74

### Re: Physics: Help with understanding Centripetal and Centrifugal forces.

Thanks for the replies. I didnt actually know there were replies because I never got an email saying there were replies. Anyways.

Thanks for the link. I read through it and it's clear now.

Thanks for you reply Bob. I understand everything you are saying, i just could not wrap my head around why centrifugal force is fictitious. I get it now and will drop the centrifugal thing and just stick with centripetal.

Thanks.

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## #6 2018-11-23 22:14:59

bob bundy
Registered: 2010-06-20
Posts: 8,541