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jackjp01
jackjp01 • Feb 6, 2009

Is flowing sand a fluid?

It appears raj87verma88 was upset about others presenting information on the fluid mechanics of sand and has now closed the thread. Anyone want to continue the debate?

Link: https://www.crazyengineers.com/forum/mechanical-civil-engineering/5850-flowing-sand-fluid.html

Take the hourglass (filled with sand) as an example. Take one out of a Boggle game, take some measurements, apply your fluids eqs, make some predictions, test and observe the FLUID properties of SAND.

How can anyone say that solids cannot act like fluids?

Check out the Wikipedia definition of a fluid: https://en.wikipedia.org/wiki/Fluid

A fluid is defined as a substance that continually deforms (flows) under an applied shear stress. All liquids and all gases are fluids. Fluids are a subset of the phases of matter and include liquids, gases, plasmas and, to some extent, plastic solids.

Fluids display such properties as:
  • not resisting deformation, or resisting it only lightly (viscosity), and
  • the ability to flow (also described as the ability to take on the shape of the container).
Sand definitely qualifies as a fluid. Non-Newtonian perhaps but still fluid. The individual sand particles themselves are obviously not a fluid but a quantity of sand particles can be considered a fluid. They do not resist plastic deformation. IE pour a bowl of sand on the ground and it does not retain the shape of the bowl. Or scoop a bowl full of sand from the ground and the sand WILL take on the shape of the bowl. "The ability to flow". Wasn't this described in the title of the original thread?
Ashraf HZ
Ashraf HZ • Feb 6, 2009
Haha, he was not upset. Anyway, since its turning into a debate, I'll move it to the correct section 😀
raj87verma88
raj87verma88 • Feb 6, 2009
That thread was quite old and was more or less inactive. That is why it was closed. You can't have old forums being bumped up after months of inactivity. You close them just like you close very old and forgotten files.
raj87verma88
raj87verma88 • Feb 6, 2009
If we consider sand to be a fluid, then we should consider cement, salt, sugar, powder, gun powder and all other crystalline elements that are in a powder form to be fluids. They flow and take the shape of the container and don't provide much resistance against deformation. Even small thermocol balls and lentil seeds are fluid to some extent. You can fill a glass with them and they will take its shape, apply force and there won't be much resistance. The list goes on.
gohm
gohm • Feb 9, 2009
Exactly, where then do you draw ther line? rocks & marbles then also would be a fluid, after all aren't they just like large grains of sand? If you magnified sand,sugar,salt, etc. within the bottle; you would see the spaces and gaps between the grains as well as the bottle, above the molecular level. Therefore, they do not count as liquids but can portray some similar properties.
mostly correct
mostly correct • Feb 19, 2009
I am not sure, but this is how I think.

Add water to the sand (There should be no chemical reaction happening)
Now you would have some mud and you can pile that up to make stuff that can hold it self up.

But if you add a kind of fluid (in the normal sense like water, mercury etc) to another kind of "normal" fluid ( !Make should that they are not chemically reacting with each other! )

You wouldn't get any thing that can pile up or hold itself up...

Well that is just a guess... anyways I think that answers the question a bit

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