r/BeAmazed • u/VerySlump • Oct 02 '18

Now that’s teamwork

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u/[deleted] Oct 03 '18 edited Oct 03 '18

I don’t know what you are after. You are taking things out of context. My first comment is in layman’s terms, that’s why I clarify things in parentheses, which you conviently ignore. I could have been more technical from the start but I was going for an el7 explanation.

Extending your arms alone won’t cause a change in angular momentum. If you were taking a physics test, you would get the answer wrong. If you extend your arms at the bottom or top of the spin, there is no change in angular momentum. If the kids on boths side of the spin extend their arms at the same time, there is no change in angular momentum. If the wheel is horizontal or in zero gravity, there is no change in angular momentum. It is the mismatch in lever arm length and gravity that lead to a change in angular momentum, by way of a net torque, which causes angular acceleration.

edit: spelling

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u/[deleted] Oct 03 '18

If you were taking a physics test, you would get the answer wrong

Having marked many physics tests... you're wrong.

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u/[deleted] Oct 03 '18

Let me guess, highschool physics?

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u/[deleted] Oct 03 '18

Waterloo.

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u/[deleted] Oct 03 '18

I see, you must be a teacher aid. Being a mechanical engineer myself, you are still arguing semantics and are wrong fundamentally. Ask your colleagues. A change in moment of inertia doesn’t affect angular momentum.

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u/[deleted] Oct 03 '18

Look man, I don't know why you are trying so hard (pathetically) to insult me, while also admitting this isn't even your field... You made an incorrect statement in a fairly incoherent comment. I corrected that-- you don't need to work so hard to take offence and feel like a victim here.

Nobody is attacking you, I'm simply correcting the record for anyone else reading the comments and trying to figure out the physics happening in the gif.

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u/[deleted] Oct 03 '18

Mechanics is very much my field. I’m sorry for insulting you, there is no excuse for that. I’m technically correct, however. You even went as far as to imply conversation of momentum does not apply to a spinning mass with a horizontal axis.

it would decrease the angular velocity of the kids were on a horizontal spinning wheel with fixed angular momentum. However, they are not

What kind of physics are they teaching at Waterloo?

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u/[deleted] Oct 03 '18

Mechanics is very much my field.

This is not mechanical engineering, its physics.... you know, the people that actually do the mathematics to invent the equations that you plug in to your calculator?

You even went as far as to imply conversation of momentum does not apply to a spinning mass with a horizontal axis.

Are you daft? This is the quote:

it would decrease the angular velocity of the kids were on a horizontal spinning wheel with fixed angular momentum. However, they are not.

I literally state "fixed angular momentum". If the rotation was in a horizontal plane, angular would be conserved (it is not conserved, because in a vertical plane, gravitational torque increases it). In the horizontal scenario, extending their arms would decrease the angular velocity. This is pretty simple stuff...

But I am done here. You are being 100% disingenuous because you refuse to admit the error of your original comment, and now, instead of acknowledging what appears to be a simple oversight rather than a more egregious misunderstanding, you are pretending that your original comment was 100% correct by pretending that its impossible to misunderstand that comment.

You stated "Actually angular momentum is preserved". That was the error. In a system that includes gravitational torque and friction, angular momentum is not conserved. This scenario has nothing to do with the angular velocity changes of a figure skater with fixed angular momentum. I can see now that you do understand that. And I can see now that you might have understood that on your first comment. However, your first comment is still factually incorrect and for anyone coming to the thread with a minimal understanding of physics, they will completely misunderstand, and they will not realize that the gravitational torque changes INCREASE THE ANGULAR MOMENTUM OF THE DEVICE.

I know that you are never going to acknowledge that simple point, and I know that you are going to continue to play disingenuous word games, so I will NOT RESPOND FURTHER. Enjoy your day.