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/sci/ - Science & Math

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4609851 No.4609851 [Reply] [Original]

So, if you were to take a pole that's one light second long, and then spin that pole around fast enough to where it completed a 360 degree rotation in 1 second making a circle that's 2 light seconds in diameter and 3.141592...light seconds in circumference...what would happen?

I guess this is a a sideways attempt to ask how is angular speed affected by relativity.

>> No.4609861

It would not be possible to spin it that fast I think.
Not without snapping.
To be able to bend, the force of where you are moving it from would have to propagate throughout the rest of the pole, this takes time.

>> No.4609862

HOLY SHIT OP I THINK YOU JUST MADE A FUCKING REVOLUTIONARY BREAK THROUGH!!!!!
GO AND PATENT THIS AND PICK UP YOUR NOBEL PRIZE RIGHT NOW!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

>> No.4609863

It would take an infinite amount of energy to do what you describe. The amount of energy it takes to accelerate something approaches infinity as speed approaches C. It doesn't matter if it is moving in a straight line or circle.

>> No.4609866

>>4609851
But let's say that the pole was perfectly rigid (which it can't be), the end of the pole would be moving faster than the speed of light... But so what?

If I had a lazer pointer strong enough to make a dot appear on the moon, and i flicked my wrist, the dot would move at faster than the speed of light across the moon....

Again I ask you, so what?

Are you going to reply that, "WELL THE LAWS OF PHYSICS SAY THAT 'NOTHING CAN MOVE FASTER THAN THE SPEED OF LIGHT'"?

Because then I'll tell you to go fuck yourself and try to find what physics REALLY say about the matter.

Sincerely yours,

Physics PhD

>> No.4609872
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4609872

>>4609866
>implying the "dot" is a moving object
nigga you ain't neva been to college, much less earned yoself any degrees

>> No.4609873

Ye gods. I didn't think I was being particularly clever with this. I was just curious how angular speed is affected by relativity. All I've ever seen is discussion of moving in a straight line and all of the reasons that was impossible, but never discussion of moving around a curve especially in terms of the rotation of a body that might have other bits not moving at nearly the same rate. I assume that there's a limit to rotational velocity, but at the same time is it actually c or some reduced factor of c found by the vector that describes the movement where the vector itself is c but the components of the vector are less than c...

>> No.4609875

>>4609866
>Sincerely yours,
>Physics PhD
oh
I see

>> No.4609876

>>4609866
It is matter that can not move faster than light.
A laser pointer does not count, it is just an image.
Shadows do not count either.

>> No.4609879

>>4609873
it's still c, also for the matter traveling they perceive the radius to get smaller

>> No.4609881

>>4609872
>>implying a dot isn't an object

Oh I see... It's NOT an object... it's a... ummm..ehhhmmmmm

>> No.4609882

>>4609876
Actually it's information can't be transfered faster than the speed of light.

Please learn physics before you try and educate others.

>> No.4609888

>>4609879
That's the part I can't quite wrap my head around. Wouldn't c along a curve cover more distance than c in a straight line? I guess a better question would be does the apparent velocity of light slow down when it goes through some gravity well (my understanding is that high enough gravity can "bend" light)? Or would it "appear" to slow down?

>> No.4609895

>>4609888
I'm not sure what kind of rationale you're using but a distance of d, regardless of wether its curved (circumfrence) or a straight line, when divided by t cannot exceed c.

Also the velocity of light appears to slow down because of the bending of space time, speed of light stays the same but appears to move slower

>> No.4609897

Time dilation will cause the tips of the rod to lag behind. It will bend until it looks like a disc, when suddenly it swallows itself and disappears from this universe never to be seen again.

>> No.4609898

>>4609895
So a pole a .5 light second in length could rotate twice as fast as one 1 slight second long, if both were rotating at the equivalent of c?

>> No.4609899

And by rotate, I mean make twice as many rotations, not rotate at a higher velocity.

>> No.4609900

>>4609899
Yes as far as I know

>> No.4609914

>>4609900
What about the rotation of a torus? Would that be similarly limited, but just any arbitrary spot on it could not go faster than c (thus making maximum number of rotations/time be a function of the outer radius)? And if it were spinning at c like a wheel, what would happen if you applied a force perpendicular to its axis of rotation?

>> No.4609918

>>4609914
>Would that be similarly limited, but just any arbitrary spot on it could not go faster than c (thus making maximum number of rotations/time be a function of the outer radius)?
That's right.

>And if it were spinning at c like a wheel, what would happen if you applied a force perpendicular to its axis of rotation?
Time dilation reduces the rotation rate; the speed remains c.

>> No.4609931

>>4609918
Last one, thanks for helping me get some small level of understanding on this.
So the faster the torus itself is moving (not rotational velocity) the slower its maximum rotational velocity can be: as in it can't rotate at c while moving forward at c? Or at least that's how it will seem because of time dilation?

>> No.4609968

>>4609931
No answer sci?

>> No.4610014
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4610014

>>4609866
>Physics PhD

>> No.4612159

>>4610014
>>posts picture mocking PhD status
>>Can't point out what's incorrect about the post

>> No.4612354

>>4609873
The strain in the material builds as you try to spin it faster. The ends DON'T accelerate linearly with distance to match the circumference of the circle on that scale. They only accelerate via relativity. So the extra acceleration goes into causing a strain on the bar. Since your bar isn't perfectly rigid, it snaps under the strain of trying to be accelerated to lightspeed, or bends backwards like a spiral.