The Normal Force on a Carousel: How Does it Affect Weighing Scales?

[Eitan Levy]

Homework Statement

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A boy with a mass of m1 is sitting in a carousel. The spinning frequency is 0.3355. The boy is also sitting on a weighing scale, will they show a number higher than m1g,lower or the same? (The mass of the weighing scale is 0).

Homework Equations

mω²r=F
ma=F
ω²=4π²f²

The Attempt at a Solution

I am trying to understand by which forces the weighing scale is affected and all I can think of is by the boy and by the normal force (and the centripetal force, but it doesn't matter here I think). Why they will show a value higher than m1g?

 

[jbriggs444]

I am trying to understand by which forces the weighing scale is affected and all I can think of is by the boy and by the normal force (and the centripetal force, but it doesn't matter here I think). Why they will show a value higher than m1g?

Always start with a free body diagram. What forces act on the boy?

What force does the scale measure directly?

 

[Eitan Levy]

Always start with a free body diagram. What forces act on the boy?

What force does the scale measure directly?

That's what I always do, the scale will show the normal power it will give to the boy I think, but why the value will be higher? I don't think I need to take the tension into consideration here, do I?

 

[jbriggs444]

That's what I always do, the scale will show the normal power it will give to the boy I think, but why the value will be higher? I don't think I need to take the tension into consideration here, do I?

See post #2.

 

[Eitan Levy]

See post #2.

Still can't figure it out.

 

[jbriggs444]

Still can't figure it out.

You did not answer the question: What forces act on the boy?

 

[Eitan Levy]

You did not answer the question: What forces act on the boy?

Normal, gravity and centripetal.

 

[haruspex]

Normal, gravity and centripetal.

Centripetal force is not an additional applied force. It is that component of the resultant of the applied forces which leads to the curvature of the path. See https://www.physicsforums.com/insights/frequently-made-errors-pseudo-resultant-forces/.

 

[Eitan Levy]

Centripetal force is not an additional applied force. It is that component of the resultant of the applied forces which leads to the curvature of the path. See https://www.physicsforums.com/insights/frequently-made-errors-pseudo-resultant-forces/.

Centripetal force is not an additional applied force. It is that component of the resultant of the applied forces which leads to the curvature of the path. See https://www.physicsforums.com/insights/frequently-made-errors-pseudo-resultant-forces/.

Okay, so the normal force, gravity and tension. Still why it will shot a value higher than m1g?

 

[haruspex]

the normal force, gravity and tension

Unless the boy is tied to the rope, tension does not act on him.

 

[Eitan Levy]

Unless the boy is tied to the rope, tension does not act on him.

Thats what I thought. So only gravity and normal? I really have no clue

 

[haruspex]

only gravity and normal

Right. What is the resultant of those two forces?

 

[Eitan Levy]

Right. What is the resultant of those two forces?

Not a native speaker, have no idea what resultant is.
Maybe the chair isn't straight anymore after the carousel starts moving and then the normal must be bigger than gravity? That's the only explanation I can think of.

 

[jbriggs444]

Not a native speaker, have no idea what resultant is.
Maybe the chair isn't straight anymore after the carousel starts moving and then the normal must be bigger than gravity? That's the only explanation I can think of.

The boy is going around on a carousel. That indicates that he is accelerating. Can you account for that with two forces, both of which are vertical?

 

[Cutter Ketch]

Not a native speaker, have no idea what resultant is.
Maybe the chair isn't straight anymore after the carousel starts moving and then the normal must be bigger than gravity? That's the only explanation I can think of.

It is hard to tell for sure from what the question says as posted. Is the thin line a cable? Is it free to swing out? However, yes, that is the usual assumption, and that is where you get your nonvertical force.

 

[Eitan Levy]

The boy is going around on a carousel. That indicates that he is accelerating. Can you account for that with two forces, both of which are vertical?

That's why I asked this question here, I was sure the chair is still straight.

 

[Cutter Ketch]

That's why I asked this question here, I was sure the chair is still straight.

The problem has an answer either way, and the answer is different depending on whether or not that vertical line is rigid. If you can't be sure from the problem statement, that is definitely something you want to clarify with the teacher.

 

[Eitan Levy]

The problem has an answer either way, and the answer is different depending on whether or not that vertical line is rigid. If you can't be sure from the problem statement, that is definitely something you want to clarify with the teacher.

My teacher unfortunately has a no questions policy, that's why I need to ask it here.

 

[jbriggs444]

To me, the drawing clearly indicates that the [platform supporting the] boy is supported by a rope, chain or cord of some sort.

 

[Cutter Ketch]

To me, the drawing clearly indicates that the [platform supporting the] boy is supported by a rope, chain or cord of some sort.

If I had to guess that would be my guess, but I'd hate to have to guess.

 

[Cutter Ketch]

My teacher unfortunately has a no questions policy, that's why I need to ask it here.

Surely when the question is unclear he/she has a responsibility to correct his/her error. Start with "your question is ambiguous" which he can't ignore and then just point and say, "Is that line rigid or free to swing out?" I find it very unlikely he would refuse to answer.

 

[haruspex]

To me, the drawing clearly indicates that the [platform supporting the] boy is supported by a rope, chain or cord of some sort.

I made the same assumption, but I'm no longer sure. Fairground carousels are of both sorts, those where the the seats tip and those where the seats remain upright, the customer relying on other restraints to provide the horizontal acceleration.
Carousels in factories and airport luggage movement tend to be level, relying on friction.
The diagram has an arrow indicating rotation, yet the support is vertical, suggesting a rigid assembly.
As Cutter Ketch observes, the answer depends critically on this.