Newtonian fluid and its antipode - what is it?

Newtonian and non-Newtonian fluids have recently attracted active interest not only from scientists but also from ordinary people. This is due to the fact that not a Newtonian fluid is easily manufactured by hand and is suitable for home experiments. First of all, let's see what kind of substances they are. The Newtonian fluid obeys Newton's law of viscous friction, and therefore received the name. According to this law, the tangential stress in the contact planes of the fluid layers is directly proportional to the derivative of the velocity of its flow along the direction of the normal to these planes.

It sounds rather difficult, but the reader will be more understandable if we say that the Newtonian fluid is water, oil, and most of the usual fluids we use everyday, that is, those that retain their aggregate state that you would not do with them If it's not about evaporation or freezing, of course). But if the dependence described in the definition above is inversely proportional, we can speak of a non-Newtonian fluid.

Such a liquid is always inhomogeneous, it contains large molecules that collect into crystal lattices, so the viscosity directly depends on the speed of the flow of the compound. The higher the speed, the higher the viscosity. Partly to this type of substances include thixotropic liquids, that is, those that change the viscosity over time, for example, putty or chocolate. Some scientists also tend to regard blood as a substance that does not act according to the laws of viscous friction of Newton, because it is an inhomogeneous fluid, it is a suspension from plasma and a variety of blood cells. Any doctor will confirm that the viscosity of the blood can vary in different parts of the vascular system, which is often a pathology. However, not every substance in principle is capable of such metamorphosis.

Non-Newtonian liquid can be prepared at home very easily. You need to take 1.5 parts of starch (ideally corn, but potato will do) and one part water. Ingredients should be mixed slowly so that there are no lumps. Ideally, it is necessary to distribute it with a rather thin layer on a baking tray, but, of course, you can experience any interactions. Try to quickly "slip" the liquid with your fingers, and it will look and feel like a frozen plastic mass. Relax your fingers and the fluid will drain. Newtonian fluid is not capable of such tricks! You can put stuff in a handful and start toss it up. Very soon it will become viscous and plastic, and that's why it's like a plait in your palms - this is a very interesting sight! Roll the liquid into a ball, it will be elastic and pleasant, but it is worth to relax your palm - it will spread. It's interesting to add dyes to it to play with the kids. Some go further and try even to run around the non-Newtonian fluid, roll things along it, but for such experiments, of course, much more material is needed than for home experiments. You can find a lot of video reports and continue to explore the fascinating world of physics.