PPRuNe Forums - View Single Post - Centripetal Vs. Centrifugal
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Old 30th March 2002 | 11:17
  #110 (permalink)  
helmet fire
20 Anniversary
 
Joined: Jul 2001
Posts: 1,084
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From: the cockpit
Cool

Wow.
We may be getting somewhere.

It seems your reason for centrifugal is that a tangential travel along line C appears to take the object away from the center at point A. In fact, you are incorrect in terms of rotational dynamics. Travel along line C may be farther away from point A, but it is not increasing radius distance at all.

Here we go with frames of reference again. Remember above we discussed the fact that frames of reference are irrelevant to the reality of the situation: i.e. just because you view it from a different point, reality is not suddenly altered.

So, if you were standing STILL at point A (not spinning), and facing line B, and simply threw the ball out in front of you, what happens? The ball moves away from point A doesnt it? In fact, if your arm action released the ball two feet from you, it would even follow line C wouldn't it? In other words, the ball follows the same path away from point A, even though no rotation was applied. SO WHERE IS THE CENTRIFUGAL FORCE?

Just because you change your reference point (spinning or not spinning), reality has not changed. The ball moves along line C for the same reason in both cases: it is released with the same motions applied to it. If it had different forces on it, the ball would necessarily follow different paths, but in our case it will not.

So, the only thing you are changing by spinning around is your frame of reference, not the forces on the ball at immediately after release - thus centrifugal cannot be supported by your arguement.

An easier way to understand this would be to imagine if you were on a moving car whilst carrying out the experiment (ie to change your frame of reference). If the car was moving parralel to line C it should be very easy for you to see that the ball does not get farther away from point A after release - thus disproving your theory.

Hopefully by now you can now see that frames of reference do not alter the forces acting on the object.

Back to your clutch now. If I get a large elastic band and wrapped it around a huge fat chick, joined the ends together and tried to pull her along, the rubber band stretches. Lets say this chick is so fat that the rubber band breaks before I can move her, can you really say that SHE applied a force to the rubber band? Obviously not. Now lets say she is running along the road and I am running along parrallel with her. Just for fun, I suddenly swerve and run away from her, and stretch the rubber band. Again the rubber band will break before she alters her course. In other words there is no difference between the two cases is there?

Now - when we were running along, did she apply ANY force to the rubber band? No. Same as the first case. The fact that she was running along a straight line is irrelevant.

Now lets say I get a rubber band that will not break. When she stands still, I pull on the rubber band and she moves toward me. Has she applied any force to the rubber band? No.

Now we are running again, but when I pull the rubber band and it doesnt break, but in fact she begins to move toward me, has she applied any force to the rubber band? Again - NO. Same forces, different frames of reference.

Now lets say I elect to stand in the same point and continue to pull the rubber band whilst she continues try and run in a straight line, and I do it four times so she has travelled in a sort of square around me. This is no different than the case of one quick pull as above is it? So has she magically started to exert a force on the rubber band just because I apply my pulling force at four seperate times? Of course not, because each time is a seperate occurence of the example as if she was standing still and I pulled her toward me - but we have just changed the frame of reference.

Now I pull her twenty times and she travels around me in a many sided twentyagonal kind of shape. Has she exerted any force on the rubber band? No. Still no. And if I pulled continuously, she would travel around me in a circle. Has this suddenly made her apply any force to the rubber band? NO NO NO NO. Therefore, centrifugal is NOT a force. Substituting the fat chick for your clutch pads, you can see that the pads apply no force of their own to the outer rim (elastic band).

But what force am I applying to the rubber band when she is standing still? I am pulling her TOWARD me. Now that you know frames of reference do not change reality, when we are turning am I not still pulling her TOWARD me (into the center)? Therefore Centripetal IS a force.

Simple hey?

Sorry for example 26. I try not to pull fat chicks now that I am older.....


edited for new format and some semblance of relevance (!!)

Last edited by helmet fire; 31st March 2002 at 10:38.
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