# Vertical centripetal motion

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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?

Thanks a ton for shedding 390-700 nm on it!

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

Thanks a ton for shedding 390-700 nm on it!

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#2

(Original post by

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?

Thanks a ton for shedding 390-700 nm on it!

**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?

Thanks a ton for shedding 390-700 nm on it!

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(Original post by

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.

**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.

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?

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#4

(Original post by

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?

**Spannerin'moi**)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?

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

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.

**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.

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(Original post by

So your question is just about weightless only?

**Kallisto**)So your question is just about weightless only?

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...

for your time!

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#7

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.

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

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.

**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.

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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#9

**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.

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#10

(Original post by

wait a min, I haven't learnt centrifugal force ...only learnt centripetal...

**Spannerin'moi**)wait a min, I haven't learnt centrifugal force ...only learnt centripetal...

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#11

**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.

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#12

(Original post by

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?

Thanks a ton for shedding 390-700 nm on it!

**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?

Thanks a ton for shedding 390-700 nm on it!

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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#13

(Original post by

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

**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

(Original post by

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...

...

**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...

...

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(Original post by

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.

**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.

(Original post by

there is no such thing as centrifugal force. in circular motion the only force ( and hence acceleration ) is centripetal... towards the centre.

**the bear**)there is no such thing as centrifugal force. in circular motion the only force ( and hence acceleration ) is centripetal... towards the centre.

(Original post by

First of all, you should define what is weightlessness. "Weightlessness" can be loosely taken as normal force is zero for the given problem.

**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

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.

**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!

a bunch!

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#15

**the bear**)

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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#16

(Original post by

I have a different view. It really depends on which frame of reference are you analyzing circular motion.

**Eimmanuel**)I have a different view. It really depends on which frame of reference are you analyzing circular motion.

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