- #1
noeszone
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Hello! First time poster, long time lurker.
I've been doing my own independent study of fluid dynamics (not recommended, i know!) and I've hit a wall. I'm trying to imagine problems of fluid dynamics other than the "river and pipe" variety to confirm that I'm really getting this drag stuff. I'm curious to know if and how the Reynolds number Re can be adapted or defined in a way to describe drag in scenarios where a fluid is encased in a solid container that's moving around? Since its essentially about contact between a solid and a fluid, I should think it could be adapted to scenarios other than pipes, etc.
I'm curious to know because ... well, here's the problem I came up with in my head that I can't figure out:
Consider the following: Two hollow metal spheres are placed at the top of a hill. They are identical in every way (total mass etc), except for one: one is filled with water, the other is filled with something very viscous such as honey or tar. They are then released from the top of the hill and roll down.
Question: Do the spheres stop rolling at the same time, or does the honey sphere stop rolling first?
My "physics intuition" tells me that the honey sphere should stop rolling first, but I can't explain why in terms of drag, Reynolds or anything. I expect the honey sphere should stop rolling first because of higher viscosity, which would facilitate transfer of gravitational potential energy to thermal energy(heat transfer) as the sphere gains kinetic energy.
For that matter, what kind of fluid flow (if any at all) should one expect inside a hollow sphere filled with water that's spinning around or rolling? I can't even VISUALIZE it and I know from gen physics that's a bad sign :) All I can see is the fluid inside "lagging" behind the solid shell part of the sphere as it rolls, and then catches up due to fluidic drag... after it catches up, is the hollow sphere with fluid filled inside essentially the same thing as a solid sphere of same mass/density? (are there any random eddies inside that bring the fluid sphere to a stop sooner?)
ANY corrections or guidance or HINTS on this is appreciated. I've been through the definitions many times so I'm not sure reiteration will help at this point... but ill do that if y'all gurus think I should :)
thanks for reading. happy holidays )
I've been doing my own independent study of fluid dynamics (not recommended, i know!) and I've hit a wall. I'm trying to imagine problems of fluid dynamics other than the "river and pipe" variety to confirm that I'm really getting this drag stuff. I'm curious to know if and how the Reynolds number Re can be adapted or defined in a way to describe drag in scenarios where a fluid is encased in a solid container that's moving around? Since its essentially about contact between a solid and a fluid, I should think it could be adapted to scenarios other than pipes, etc.
I'm curious to know because ... well, here's the problem I came up with in my head that I can't figure out:
Consider the following: Two hollow metal spheres are placed at the top of a hill. They are identical in every way (total mass etc), except for one: one is filled with water, the other is filled with something very viscous such as honey or tar. They are then released from the top of the hill and roll down.
Question: Do the spheres stop rolling at the same time, or does the honey sphere stop rolling first?
My "physics intuition" tells me that the honey sphere should stop rolling first, but I can't explain why in terms of drag, Reynolds or anything. I expect the honey sphere should stop rolling first because of higher viscosity, which would facilitate transfer of gravitational potential energy to thermal energy(heat transfer) as the sphere gains kinetic energy.
For that matter, what kind of fluid flow (if any at all) should one expect inside a hollow sphere filled with water that's spinning around or rolling? I can't even VISUALIZE it and I know from gen physics that's a bad sign :) All I can see is the fluid inside "lagging" behind the solid shell part of the sphere as it rolls, and then catches up due to fluidic drag... after it catches up, is the hollow sphere with fluid filled inside essentially the same thing as a solid sphere of same mass/density? (are there any random eddies inside that bring the fluid sphere to a stop sooner?)
ANY corrections or guidance or HINTS on this is appreciated. I've been through the definitions many times so I'm not sure reiteration will help at this point... but ill do that if y'all gurus think I should :)
thanks for reading. happy holidays )
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