username2889812
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2.2 kg bucket half filled with water is swung in vertical circle- radius of 1.2 m. What's the speed of bucket at top of its swing in order to be weightless...


So at the top, I know there are both tension forces and weight acting downwards...is that why it's weightless?:hmmmm:

Thanks a ton for shedding 390-700 nm on it!
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Kallisto
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(Original post by Spannerin'moi)
2.2 kg bucket half filled with water is swung in vertical circle- radius of 1.2 m. What's the speed of bucket at top of its swing in order to be weightless...


So at the top, I know there are both reaction forces and weight acting downwards...is that why it's weightless?:hmmmm:

Thanks a ton for shedding 390-700 nm on it!
So your question is just about weightless only? the speed of the bucket is so fast that it comes to a force (centrifugal force) which is not only equal in value to gravitational force, but also opposite in direction at the top. That is the reason.
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(Original post by Kallisto)
So your question is just about weightless only? the speed of the bucket is so fast that it comes to a force (centrifugal force) which is not only equal in value to gravitational force, but also opposite in direction at the top. That is the reason.
:ta: a ton for the explanation!
So the tension from the hand cause centrifugal force right? That means the force is acting toward the centre of circle...so won't there be tension and weight acting downward direction at the top of the swing?:hmmmm:
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Kallisto
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(Original post by Spannerin'moi)
:ta: a ton for the explanation!
So the tension from the hand cause centrifugal force right? That means the force is acting toward the centre of circle...so won't there be tension and weight acting downward direction at the top of the swing?:hmmmm:
At the top the direction of the centrifugal force is upwards and the one of gravitational force downwards. The latter goes to the center of the circle, the first named goes away from it.

When the hand is swinging a bucket in circular motion, it comes to tension what leads to centrifugal force, so yes.
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(Original post by Kallisto)
At the top the direction of the centrifugal force is upwards and the one of gravitational force downwards. The latter goes to the center of the circle, the first named goes away from it.

When the hand is swinging a bucket in circular motion, it comes to tension what leads to centrifugal force, so yes.
Ohh I see... thanks a lot for the help!
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(Original post by Kallisto)
So your question is just about weightless only?
You're right...um...how do we find out reaction forces?
I made sure centripetal acceleration = weight + reaction force

mv^2/r. =. mg + R
when I tried to make subject as v, I'm stuck at R...

:ta: for your time!
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Kallisto
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If it is about reaction and action, reaction force is the counterpart to action force. In other words: it is a force opposite to action force. The question is: what is action force? if the action force is the centrifugal force, the reaction force can just be the centripedal force, as the centripedal force is always opposite to the centrifugal force in every moment of the circular motion!

But why you are interest in reaction force? according to the question above, the speed has to be determine and you can find the speed out by converting the centrifugal force to the unit v.
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(Original post by Kallisto)
If it is about reaction and action, reaction force is the counterpart to action force. In other words: it is a force opposite to action force. The question is: what is action force? if the action force is the centrifugal force, the reaction force can just be the centripedal force, as the centripedal force is always opposite to the centrifugal force in every moment of the circular motion!

But why you are interest in reaction force? according to the question above, the speed has to be determine and you can find the speed out by converting the centrifugal force to the unit v.
wait a min, I haven't learnt centrifugal force ...only learnt centripetal...

I have no clue how to convert centrifugal force to the unit v...

And would you disagree with this equation?

(mv^2)/r = mg + R
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Eimmanuel
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(Original post by Kallisto)
So your question is just about weightless only? the speed of the bucket is so fast that it comes to a force (centrifugal force) which is not only equal in value to gravitational force, but also opposite in direction at the top. That is the reason.
I doubt weightlessness has to do with centrifugal force. I recommend you learn what is weightlessness first. I don't think students are required to know what is centrifugal force at A level.
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(Original post by Spannerin'moi)
wait a min, I haven't learnt centrifugal force ...only learnt centripetal...
there is no such thing as centrifugal force. in circular motion the only force ( and hence acceleration ) is centripetal... towards the centre.
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(Original post by Kallisto)
If it is about reaction and action, reaction force is the counterpart to action force. In other words: it is a force opposite to action force. The question is: what is action force? if the action force is the centrifugal force, the reaction force can just be the centripedal force, as the centripedal force is always opposite to the centrifugal force in every moment of the circular motion!

But why you are interest in reaction force? according to the question above, the speed has to be determine and you can find the speed out by converting the centrifugal force to the unit v.
Again highly recommend that you re-study what is action and reaction force. You are also confused with what is frame of reference.
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Eimmanuel
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(Original post by Spannerin'moi)
2.2 kg bucket half filled with water is swung in vertical circle- radius of 1.2 m. What's the speed of bucket at top of its swing in order to be weightless...


So at the top, I know there are both tension forces and weight acting downwards...is that why it's weightless?:hmmmm:

Thanks a ton for shedding 390-700 nm on it!
First of all, you should define what is weightlessness. "Weightlessness" can be loosely taken as normal force is zero for the given problem.

You are right that at the top, if the bucket of water is moving fast enough, the tension and weight will be acting downward or toward the center of the circular motion.
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Eimmanuel
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(Original post by Spannerin'moi)
wait a min, I haven't learnt centrifugal force ...only learnt centripetal...

I have no clue how to convert centrifugal force to the unit v...

And would you disagree with this equation?

(mv^2)/r = mg + R
At the top of circular motion, your equation of motion or N2L equation is correct.

(Original post by Spannerin'moi)
2.2 kg bucket half filled with water is swung in vertical circle- radius of 1.2 m. What's the speed of bucket at top of its swing in order to be weightless...
...
To solve this problem using (mv^2)/r = mg + R, you set R = 0.
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(Original post by Eimmanuel)
I doubt weightlessness has to do with centrifugal force. I recommend you learn what is weightlessness first. I don't think students are required to know what is centrifugal force at A level.
True...I should :yes:
(Original post by the bear)
there is no such thing as centrifugal force. in circular motion the only force ( and hence acceleration ) is centripetal... towards the centre.
Ohh I see...:ta:
(Original post by Eimmanuel)
First of all, you should define what is weightlessness. "Weightlessness" can be loosely taken as normal force is zero for the given problem.
(Original post by Eimmanuel)
At the top of circular motion, your equation of motion or N2L equation is correct.



To solve this problem using (mv^2)/r = mg + R, you set R = 0.

Got it...so it simply means no normal reaction force!
:ta: a bunch!
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(Original post by the bear)
there is no such thing as centrifugal force. in circular motion the only force ( and hence acceleration ) is centripetal... towards the centre.
I have a different view. It really depends on which frame of reference are you analyzing circular motion.
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(Original post by Eimmanuel)
I have a different view. It really depends on which frame of reference are you analyzing circular motion.
for school exams it is best to keep it straightforward
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