What are non-Newtonian fluids? Examples can certainly be found even in your refrigerator, but quicksand is considered the most obvious example of a scientific miracle - flowing and solid at the same time thanks to suspended (suspended) particles.
About viscosity
Sir Isaac Newton argued that viscosity, or fluid resistance to flow, depends on temperature. So, for example, water can turn into ice and vice versa under the influence of heating or cooling elements. However, some substances that exist in the world change viscosity due to the use of force, and not a change in temperature. Interestingly, the universally used tomato sauce is considered to be a non-Newtonian fluid, which becomes thinner with prolonged stirring. Cream, on the contrary, thickens when whipped. These substances are not important temperature - the viscosity of non-Newtonian fluids varies due to physical effects.
Experiment
For those who are interested in applied science or just want to impress their guests and friends with an incredibly simple and at the same time stunningly fascinating scientific experiment, a special recipe for colloidal starch solution has been created. Real non-Newtonian liquid, made literally from two ordinary culinary ingredients with its own hands, will amaze both schoolchildren and students with its consistency. You will need only starch and pure water, and in the end you will get a unique substance, which is both a liquid and a solid.
Recipe
- Pour about a quarter of a package of corn starch into a clean bowl and slowly pour in about half a glass of water. Get in the way. Sometimes it is more convenient to prepare a colloidal starch solution directly with your hands.
- Continue to add starch and water in small portions until you get a substance that, in consistency, resembles honey. This is the future non-Newtonian fluid. How to make it homogeneous if all attempts at uniform stirring end in failure? Do not worry; just give the process more time. As a result, one package of corn starch will most likely take from one to two glasses of water. Please note: the substance becomes more dense as you add more and more powder to it.
- Pour the resulting substance into a pan or baking dish. Take a closer look at its unusual consistency while the “solid” liquid pours down. Stir the substance in a circle with your index finger - first slowly, then faster and faster until you get an amazing non-Newtonian fluid.
Experiences
Both for the purposes of scientific knowledge, and just for fun, you can try to conduct the following experiments:
- Swipe your finger over the surface of the resulting clot. Have you noticed anything?
- Immerse the entire hand in a mysterious substance and try to squeeze it with your fingers and pull it out of the container.
- Try to roll the substance in your palms to make a ball.
- You can even slap a clot with your palm with all your strength. Present spectators will probably scatter to the side, expecting that they will now be sprayed with starch solution, but an unusual substance will remain in the container. (Unless, of course, you spared starch.)
- A spectacular experiment is offered by video bloggers. For it, you will need a speaker, which should be carefully wrapped in thick layers of thick cling film. Pour the solution onto the tape and turn on the music at high volume. You will be able to observe stunning visual effects, possible only with this unique composition.
If you are conducting an experiment in a laboratory in front of schoolchildren or students, ask them why non-Newtonian fluid behaves this way. For what reason does it seem to be a solid body if you squeeze it in your hand, but it flows like syrup if you unclench your fingers? At the end of the discussion, you can pack the clot in a large plastic bag with a zipper to save it until the next time. It is useful to you to demonstrate the properties of the suspension.
Mystery of substance
Why, in some cases, colloidal starch solution behaves like a solid, and in others like a liquid? In fact, you created a real non-Newtonian fluid - a substance that rejects the law of viscosity.
Newton believed that the viscosity of a substance changes only due to an increase or decrease in temperature. For example, engine oil flows easily when heated and becomes particularly thick when cooled. Strictly speaking, non-Newtonian fluids also obey this physical law, but their viscosity can also be changed by applying force or pressure. When you squeeze a colloid clot in your hand, its density increases significantly, and (even if only temporarily) it seems to turn into a solid. When you open your fist, the colloidal solution flows like an ordinary liquid.
What you need to keep in mind
The irony is that it is impossible to mix starch with water forever, because as a result of the experiment you get not a homogeneous substance, but a suspension. Over time, the powder particles will exfoliate from the water molecules and collect in a solid lump at the bottom of your plastic bag. It is for this reason that such a non-Newtonian fluid instantly clogs sewer pipes, if you just take and pour it into the sink. In no case do not pour it into the drain - it is better to pack it in a bag and just throw it into the garbage chute.