Balancing of rotating masses

  • Thread starter koolraj09
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  • #1
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Main Question or Discussion Point

Hi guys.
Firstly I want to know what is inertia force? Is it a real force?
Then regarding balancing of rotating masses, why is unbalanced caused by a centrifugal force? I mean I've learnt in my intermediate that centrifugal force is a pseudo force and it is only to be taken into consideration when we are in non inertial frame of reference. That means centrifugal force(& indirectly unbalance) will come into picture only when we're in non-inertial frame of reference. But this doesn't happen in reality. What is the reason behind this paradox?
Can anyone explain?
Thanks.
 

Answers and Replies

  • #2
tiny-tim
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hi koolraj09! :smile:
I mean I've learnt in my intermediate that centrifugal force is a pseudo force and it is only to be taken into consideration when we are in non inertial frame of reference. That means centrifugal force(& indirectly unbalance) will come into picture only when we're in non-inertial frame of reference. But this doesn't happen in reality.
it does happen in reality …

in reality, we often prefer a https://www.physicsforums.com/library.php?do=view_item&itemid=87"

for example, in any vehicle turning in a circle, calculating forces within the vehicle is far easier in a rotating frame :smile:

(and, by coincidence, I've just written in https://www.physicsforums.com/showthread.php?p=3028090" in a rotating frame)
Then regarding balancing of rotating masses, why is unbalanced caused by a centrifugal force?
i don't understand :confused:
 
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  • #3
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Hi tiny tim.
What I mean to say is consider a rotating shaft. If the shaft is unbalanced it means that it's c.g. is not at the axis of rotation. Then comes into play our centrifugal force...this is quoted by most of the textbooks.
So what I really want to ask is that in reality the shaft is really unbalanced. But if we look from non inertial frame of reference then shaft is unbalanced because centrifugal force is there in this case. Now if we look at the shaft from an non-inertial frame of reference then it's perfectly balanced. But it's contradictory to reality.
 
  • #4
tiny-tim
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Now if we look at the shaft from an non-inertial frame of reference then it's perfectly balanced.
no!

the shaft is not balanced, because the axle can feel the shaft tugging at it … if the shaft came loose from the axle, it would fly away (instead of continuing to rotate on the spot)

in the https://www.physicsforums.com/library.php?do=view_item&itemid=87" from the axle on the shaft, radially inward from the c.o.m.

… it balances the centrifugal force, keeping the shaft in equilibrium

(if the c.o.m. was at the axle, the shaft would be balanced, and there would be no reaction force)

in the inertial frame, there is the same reaction force

… it has no force balancing it, and so the c.o.m is forced to accelerate towards the axle, resulting (obviously! :rolleyes:) in a rotation

in either frame the shaft is unbalanced …

if the connection is broken, the shaft will fly off​
 
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