# Decrease in viscosity upon rapid decelleration

I'm in search of a material that decreases in viscosity with acceleration. In this case, I really mean decelleration, but a change of velocity nonetheless. My questions:

1. Could such a material exist? Does Such a material exist? If so, what is it?
2. Would a material with said properties inside a container, subject to rapid deceleration, have more of a tendency to remain on its forward course than a solid body of equal mass in the same situation?
3. How can I mathematically describe the behavior of this material?

## Answers and Replies

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Cornstarch

There are other non-newtonian fluids but this is one which has the properties you ask.

Ketchup has the reverse property of becoming less viscous on (+ve) acceleration and is called thixotropic.

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I've played with cornstarch and water before, is that not the opposite of what I'm looking for? Are there any other examples of thixotropic fluids? They seem like what I'm looking for.

Bentonite is thixotropic.

mfb
Mentor
2. Would a material with said properties inside a container, subject to rapid deceleration, have more of a tendency to remain on its forward course than a solid body of equal mass in the same situation?
F=m*a is the same independent of the material itself. I am not sure what exactly you mean with "tendency to remain on its forward course", but inertia is the same.

Edit: This is a test of a bug.

Correct regarding the variation along those two axis. Also correct that there is no component in the ##\hat\phi# direction, but do you think the magnetic field varies as ##\phi## varies? or does it have ##\phi## (azimuthal) symmetry?

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Chestermiller
Mentor
The viscosity of a non-Newtonian fluid is not related to its acceleration. It is determined by the second invariant of the rate of deformation tensor. Even in fluid flows for which there is no acceleration, such as simple shear, the viscosity is altered in response to the deformation. There are some non-Newtonian fluids that exhibit shear thinning, or thixotropy, in which the viscosity decreases with increases in the shear rate. There are other non-Newtonian fluids that exhibit shear thickening, or dilatancy, in which the viscosity increases with increases in shear rate. This is just a small subset of the types of non-Newtonian fluid behavior that is encountered in practice. Some polymer solutions and melts exhibit viscoelasticity, in which the shear stress relaxes with time after a sudden shear deformation is imposed. If you would like to learn more about the non-Newtonian behavior of fluids, see Transport Phenomena by Bird, Stewart, and Lightfoot.