There is no such thing as centrifugal force!

Pudney · 11 Jul 2006 at 10:47

From my understanding centrefugal force is created by an object moving in a circular motion whereas centrepetal force is acted upon the object if that makes sense. Although that is a simplification of the situation.

kaiowas · 11 Jul 2006 at 11:05

Who cares what the forces are called. The most importasnt thing is that you can spin a bucket of water around your head without getting wet.

AS_Platinum · 11 Jul 2006 at 11:19

Who cares what the forces are called. The most importasnt thing is that you can spin a bucket of water around your head without getting wet.

Not if someone throws a bucket of water over you while your looking like a pratt you can't

King4aDay · 11 Jul 2006 at 11:22

kaiowas said:
Who cares what the forces are called. The most importasnt thing is that you can spin a bucket of water around your head without getting wet.

Nah, the most important thing is being able to pass a 'cigarette' to your friend further down the beach inside the rim of a frisbee

.

Psycho Sonny · 11 Jul 2006 at 11:28

JRS said:
From the comic genious of xkcd:

rofl who would have thought it?

Wryel · 11 Jul 2006 at 12:13

I was taught that centrifugal force was a 'fictitious force' - and its only present depending on your frame of reference. When you move in a circle you are accelerating towards the centre, so that is the direction of the force.

titchard · 11 Jul 2006 at 12:55

so, by this, all them rides (i.e. the one where your in the cylinder and it spins and keeps you pressed against the sides)

Does so by Centripedal forces, not centrifugal?

Wow! never knew that, need to read up what this fictious centrifugal force actually is!

Rich

Arcade Fire · 11 Jul 2006 at 13:50

When you're in a rotating reference frame (i.e. you're in something that's spinning) you feel forces which aren't really there, and are merely caused by the face that you're rotating. These are called 'fictitious forces'. Using Newton's law 'Force = Mass x Acceleration' for a body in a rotating frame, you have

Actual Force = Mass x (Perceived acceleration in rotating frame + Centripetal acceleration + Coriolis acceleration)

You can do a cunning little rearrangement to give

Mass x Perceived acceleration = Actual Force - (Mass x Centripetal acceleration) - (Mass x Coriolis acceleration)

So in a rotating frame, you feel accelerations (the centripetal and coriolis accelerations) that aren't actually caused by any forces, but are just caused by the fact that you're rotating. The expression 'Mass x Centripetal Acceleration' is what's called the centrifugal force - even though there's no force there.

So there's no such thing as a centrifugal force, but you can feel an acceleration just as if there was one.

Edit: Also, for christ's sake, it's centripetal not centripedal!
http://www.google.co.uk/search?hl=en&q=define:+centripedal&meta=

calnen · 11 Jul 2006 at 14:02

Arcade Fire said:
When you're in a rotating reference frame (i.e. you're in something that's spinning) you feel forces which aren't really there, and are merely caused by the face that you're rotating. These are called 'fictitious forces'. Using Newton's law 'Force = Mass x Acceleration' for a body in a rotating frame, you have

Actual Force = Mass x (Perceived acceleration in rotating frame + Centripetal acceleration + Coriolis acceleration)

You can do a cunning little rearrangement to give

Mass x Perceived acceleration = Actual Force - (Mass x Centripetal acceleration) - (Mass x Coriolis acceleration)

So in a rotating frame, you feel accelerations (the centripetal and coriolis accelerations) that aren't actually caused by any forces, but are just caused by the fact that you're rotating. The expression 'Mass x Centripetal Acceleration' is what's called the centrifugal force - even though there's no force there.

So there's no such thing as a centrifugal force, but you can feel an acceleration just as if there was one.

Edit: Also, for christ's sake, it's centripetal not centripedal!
http://www.google.co.uk/search?hl=en&q=define:+centripedal&meta=

Just quoting it so everybody reads

This man knows his stuff, and isnt too lazy to actually write it. Hooray!

benjo plz. · 11 Jul 2006 at 14:04

laissez-faire said:
Doing a degree in Physics at Edinburgh we were told that the Centrifugal force is the normal reaction to the centripetal force... It does exist.

Does that make them equal in magnitude to each other?

aardvark · 11 Jul 2006 at 14:05

or you could just read the wikipedia link:

Centrifugal force (from Latin centrum "center" and fugere "to flee") is a term which may refer to two different forces which are related to rotation. Both of them are oriented away from the axis of rotation, but the object on which they are exerted differs.

* The reactive centrifugal force is the reaction to the centripetal force [1]. This is equal in magnitude to the centripetal force, directed away from the center of rotation, and is exerted by the rotating object upon the object which exerts the centripetal force. As it is an actual force, it is always present, independent of the choice of reference frame. Note that this Newtonian use of the term centrifugal force is rare in modern discussions.

* The fictitious centrifugal force appears when a rotating reference frame is used for analyzing the system. The centrifugal force is exerted on all objects, and directed away from the axis of rotation.

Arcade Fire · 11 Jul 2006 at 14:58

The reactive centrifugal force is completely different to what most people think of when they hear the term 'centrifugal force' though.

Van_Dammesque · 11 Jul 2006 at 16:09

The way I think of it is this:
Imagine you have a heavy small ball attatched to a piece of string. You pick it up and start spinning it above your head. The centripetal is felt by the ball, the centrifugal force is the tension in the string, i.e it is the opposite to centripetal force.

DRZ · 11 Jul 2006 at 16:35

Thank you Mr Arcade Fire for putting it better than I would have bothered to

Oh and yes, the whole pedal thing is as annoying to me as it appears it is to you as well

Bubo · 11 Jul 2006 at 16:36

This confusion is all down to Magnus Pike. The first time I heard the word centrifugal was on that 70's popular science TV programme on ITV, which annoyingly I can't remember the name of. I went round proudly saying centrifugal this and centrifugal that, cos if Magnus Pike had said it, it was gosel, simple as that. Wasn't until I went to grammar school I found it its actually centripetal. So I conclude those who think its centrifugal have a) been exposed to Magnus Pike as a 7 year old and b) never been to grammar school.

Psyk · 11 Jul 2006 at 16:58

The easiest way to imagine why the fake centrifugal force isn't a real force is to imagine you're in an accelerating car. When the car accelerates forwards it feels like you're being pushed backwards when really you know that it's because the car is pushing you forwards. The same applies to something that's going in a circle. You're being accelerated towards the centre of the circle so it feels like you're being pushed the other way.

AJUK · 11 Jul 2006 at 17:01

laissez-faire said:
Doing a degree in Physics at Edinburgh we were told that the Centrifugal force is the normal reaction to the centripetal force... It does exist.

As a reaction, yes but you cannot have a centrifugal 'reaction' without a centripedal force in the first place. That isn't true of other forces. Therefore, it is a perceived force.

Arcade Fire · 11 Jul 2006 at 17:08

Psyk said:
The easiest way to imagine why the fake centrifugal force isn't a real force is to imagine you're in an accelerating car. When the car accelerates forwards it feels like you're being pushed backwards when really you know that it's because the car is pushing you forwards. The same applies to something that's going in a circle. You're being accelerated towards the centre of the circle so it feels like you're being pushed the other way.

Ooh, good analogy. I'll have to remember that one!

Wryel · 11 Jul 2006 at 17:50

Arcade Fire said:
When you're in a rotating reference frame (i.e. you're in something that's spinning) you feel forces which aren't really there, and are merely caused by the face that you're rotating. These are called 'fictitious forces'. Using Newton's law 'Force = Mass x Acceleration' for a body in a rotating frame, you have

Actual Force = Mass x (Perceived acceleration in rotating frame + Centripetal acceleration + Coriolis acceleration)

You can do a cunning little rearrangement to give

Mass x Perceived acceleration = Actual Force - (Mass x Centripetal acceleration) - (Mass x Coriolis acceleration)

So in a rotating frame, you feel accelerations (the centripetal and coriolis accelerations) that aren't actually caused by any forces, but are just caused by the fact that you're rotating. The expression 'Mass x Centripetal Acceleration' is what's called the centrifugal force - even though there's no force there.

So there's no such thing as a centrifugal force, but you can feel an acceleration just as if there was one.

Edit: Also, for christ's sake, it's centripetal not centripedal!
http://www.google.co.uk/search?hl=en&q=define:+centripedal&meta=

Sounds like you did exactly the same mechanics course I did whilst doing physics.