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Old 09-08-2017, 03:54 PM
pohjonen pohjonen is offline
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Why are hurricanes structured like galaxies?

With all the pictures of hurricanes taken from space lately, I can't help but note the similarity between the shapes of hurricanes and galaxies, right down to the wispy arms and centers (black holes, and eyes). I was going to google for the reason, but was unsure how to word it. Can any dopers answer this for me? Thanks.
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Old 09-08-2017, 03:59 PM
pohjonen pohjonen is offline
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By the way, I know that all galaxies don't have that shape.
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Old 09-08-2017, 04:00 PM
Grrr! Grrr! is offline
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Centripetal force at work. Both entities spin which is going to give similar visual effects.
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Old 09-08-2017, 04:01 PM
Procrustus Procrustus is online now
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I googled your OP title and got this
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Old 09-08-2017, 04:19 PM
watchwolf49 watchwolf49 is offline
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They are both vortices ...
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Old 09-08-2017, 04:28 PM
John Mace John Mace is online now
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Quote:
Originally Posted by Grrr! View Post
Centripetal force at work. Both entities spin which is going to give similar visual effects.
The forces at work in Hurricanes are not centripetal, as in a gravitational field. It's much more complicated, and relates to the Coriolis effect.

Last edited by John Mace; 09-08-2017 at 04:30 PM.
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Old 09-08-2017, 07:53 PM
pohjonen pohjonen is offline
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They are both vortices ...
This makes sense. Am I correct in understanding that the vortices of hurricanes are caused by temperature variations?
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Old 09-08-2017, 08:04 PM
Chronos Chronos is offline
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John Mace, there are centripetal forces at work in anything that's moving in a circle. Gravity is one common source of centripetal force, but it's not the only one. In a hurricane, the centripetal forces come from the pressure difference between the low-pressure center and the high-pressure outside.

And to the OP, while all or almost all galaxies have a supermassive black hole in the center, it won't show up in a picture of the whole galaxy, the way a hurricane's eye would. The central black hole, or even its accretion disk, is far, far smaller than the galaxy as a whole.
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Old 09-08-2017, 08:13 PM
Saint Cad Saint Cad is online now
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Originally Posted by Grrr! View Post
Centripetal force at work. Both entities spin which is going to give similar visual effects.
Are you sure? I would think it is conservation of angular momentum.
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Old 09-08-2017, 08:23 PM
Chronos Chronos is offline
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Centripetal force and angular momentum are two concepts which can't really be disentangled from each other, since they'll both show up every time you have rotation.
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Old 09-09-2017, 12:14 AM
watchwolf49 watchwolf49 is offline
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Chronos is correct, the word "centripetal" only defines the direction of the force, towards the center ... in a galaxy, this centripetal force is caused by gravity; in a hurricane this centripetal force is caused by the pressure force; so both are correct usages ...

We have to be very careful applying the conservation of angular momentum to a hurricane or any cyclone ... these particular vortices are under torque, so angular momentum is increasing until they reach their frictional limits ... one thing a galaxy doesn't do is precipitate water vapor so this can't be relied upon to explain torque there, not sure we can say galaxies are even under torque ... but either way, they can both be explained as vortices and all the vortex equations will hold true ...

No one knows why an eye forms at the center of a hurricane, so we don't know why galaxies don't have eyes ... research continues ...

Last edited by watchwolf49; 09-09-2017 at 12:15 AM. Reason: Wake up to find out that you are the eyes of the world ...
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Old 09-09-2017, 12:20 AM
watchwolf49 watchwolf49 is offline
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Originally Posted by pohjonen View Post
This makes sense. Am I correct in understanding that the vortices of hurricanes are caused by temperature variations?
Pressure variations, which could be in turn caused by temperature variations, but there are other mechanics that can cause these initiating pressure variations ... once the initial vortex is formed and water starts condensing, then it's just balls out torque that drives the hurricane ...

Last edited by watchwolf49; 09-09-2017 at 12:22 AM.
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Old 09-09-2017, 12:24 AM
Beckdawrek Beckdawrek is offline
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The swirl shape is a constant in nature..i learned that in art school..not science-y....i know..forgive me
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Old 09-09-2017, 12:29 AM
watchwolf49 watchwolf49 is offline
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Thank you Beckdawrek ... sometimes we delve too deep into the science of nature we sometimes forget just how beautiful these things are ...
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Old 09-09-2017, 07:03 PM
Beckdawrek Beckdawrek is offline
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You're welcome
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Old 09-10-2017, 07:21 AM
Chronos Chronos is offline
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Apparently, you're not the only one who's noticed this, as evidenced by today's Schlock Mercenary.
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Old 09-10-2017, 08:42 AM
Isilder Isilder is offline
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Quote:
Originally Posted by Chronos View Post
Centripetal force and angular momentum are two concepts which can't really be disentangled from each other, since they'll both show up every time you have rotation.
worse, "momentum" has no physical manifestation. Its a 4th rule to help apply Newston's 3.. basically momentum is a corollary of Newton's law "every action has equal and opposite" , its listed as different because its extended to apply over definite time frames... The momentum must be conserved , or the change must be due to external influences.
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Old 09-10-2017, 05:01 PM
Chronos Chronos is offline
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Beg pardon? Of course momentum (linear and angular) has a physical manifestation. In what sense doesn't it?
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Old 09-11-2017, 04:38 PM
Irishman Irishman is online now
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Momentum is the manifestation of the first two of Newton's Laws.

An object in motion tends to stay in motion. --> Momentum

An object at rest tends to stay at rest. --> Momentum

For every action, there is an equal and opposite reaction. --> Forces apply both directions: on this from that and from this on that.

F= m a is really a simplification for constant mass. With variable mass, mass changes with time, such that

If P(t) = momentum = m(t) v(t), then

F = m(t) dv/dt - u dm/dt

Where u = the velocity of the ejected/accreted mass as seen in the object's rest frame, also called the ejection velocity.
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Old 09-11-2017, 04:52 PM
watchwolf49 watchwolf49 is offline
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Kitchen counter science:

Cupboard door of mass m traveling at velocity v has enough momentum p to create bruise diameter douch on forehead ...

Last edited by watchwolf49; 09-11-2017 at 04:53 PM. Reason: Don't try this at home ...
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Old 09-11-2017, 04:59 PM
Chronos Chronos is offline
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Energy is usually more relevant than momentum, for inflicting damage.
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Old 09-11-2017, 05:18 PM
watchwolf49 watchwolf49 is offline
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For m = 500 g and v = 1 m/s, I have douch = 2.5 cm ... we need someone to try 2 m/s now ...
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Old 09-11-2017, 10:18 PM
Beckdawrek Beckdawrek is offline
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Every body should just take an art class...and feel the happy happy swirl/galaxy/hurricane shape!
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Old 09-12-2017, 07:39 AM
DesertDog DesertDog is offline
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One thing to keep in mind is that the structure of galaxies is preserved only because the outer parts of the disk are rotating faster than they ought to be. If they weren't, those beautiful trailing arms would have smeared into nothingness long ago.

The best explanation for this is dark matter, but its description smacks of Handwavium* to me.

*"There is this stuff we need to have around to explain some phenomena we see, but we have no way of detecting it except its gravitational effects. Oh, yeah, we need to have five times of the stuff as there is of ordinary matter to make it work."
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Old 09-12-2017, 10:45 PM
race_to_the_bottom race_to_the_bottom is offline
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The similarities of spiral galaxies and hurricanes are only superficial. The structure of spiral galaxies is not completely understood.
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