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Granular Materials: Liquid-like Properties of Sand - page 3 / 14





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rate to fluidize the sand, the sand’s property changes from a solid, to a liquid where

objects start to sink, then to a liquid with bubbles. We will try to concentrate on the

middle regime.

There are many interesting things to study with a fluidized bed or with sand itself.

Leo P. Kadanoff, O. Zik, et al.5 have many categories in which sand is interesting to

study. For example, in a fluidized bed sand undergoes convection where as the solid

state of sand the top only moves. In our experiment, we have studied the fluidity in a

fluidized bed of sand.

One of the main differences between a solid and a liquid is that in a solid there is

an elastic constant where as a liquid has viscosity, where viscosity is the resistance to

flow. A liquid cannot withstand shear forces so it cannot support a heavy object. A liquid

wants to keep on flowing while a solid wants to spring back into its original position.

What we were initially looking at is if sand in its fluidized state acts as a liquid with

constant viscosity, otherwise known as a Newtonian liquid. If a force is applied to a

sphere immersed in a Newtonian liquid, the sphere reacts with a drag force. This drag

force is found to be directly proportional to the viscosity (), velocity (v), and the size of

the ball (a) for low speeds of the ball. This gives us drag force in a Newtonian liquid as

FDrag = (6   v a), called the Stokes Drag. In our experiment, we want to find out

whether the fluidized bed of sand obeys the same exact equation as a liquid. This means

that holding everything constant, we would see whether the viscosity is a constant or a

function of maybe it’s velocity, or even a function of grain size, object size, or gas flow



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