Newtonian and non-Newtonian fluids have recently attracted active interest not only of scientists, but also of ordinary people. This is due to the fact that non-Newtonian fluid is easy to make with your own hands and is suitable for home experiments. To begin with, let's figure out what kind of substances they are in general. Newtonian fluid obeys Newton's law of viscous friction, which is why it got its name. According to this law, the shear stress in the planes of contact between the layers of a liquid is directly proportional to the derivative of the velocity of its flow in the direction normal to these planes.
It sounds rather complicated, but it will be more clear to the reader if we say that the Newtonian fluid is water, oil and most of the fluid substances familiar to us in daily use, that is, those that retain their state of aggregation, whatever you did not do with them (unless we are talking about evaporation or freezing, of course). But if the dependence described in the definition above is inversely proportional, we can talk about a non-Newtonian fluid.
Such a liquid is always heterogeneous, it contains large molecules that gather into crystal lattices, so the viscosity directly depends on the flow rate of the compound. The higher the speed, the greater the viscosity. In part, this type of substance includes thixotropic liquids, that is, those that change viscosity over time, such as putty or chocolate. Also, some scientists tend to consider blood as a substance that does not act according to Newton's laws of viscous friction, because it is an inhomogeneous liquid, it is a suspension of plasma and many blood cells. Any doctor will confirm that blood viscosity can vary in different parts of the vascular system, which is often a pathology. However, not every substance is in principle capable of such metamorphoses.
Non-Newtonian fluid can be made very easily at home. You need to take 1.5 parts of starch (ideally corn, but potato will do) and one part of water. The ingredients should be mixed slowly so that there are no lumps. Ideally, you should spread it in a fairly thin layer on a baking sheet, but, of course, any interactions can be experienced. Try to quickly "shovel" the liquid with your fingers, and it will look and feel like a frozen plastic mass. Relax your fingers and the liquid will drain. Newtonian fluid is not capable of such tricks! You can take the substance in a handful and start throwing it up. Very soon it will become viscous and plastic, and therefore it will seem to dance in your palms - this is a very interesting sight!Roll the liquid into a lump, it will be elastic and pleasant, but if you relax your palm, it will spread. It is interesting to add dyes to it to play with children. Some go further and even try to run on a non-Newtonian fluid, roll objects on it, and so on, but for such experiments, of course, much more material is needed than for home experiments. You can find many video reports and continue to explore the fascinating world of physics.
