Walking on water: is this a liquid or a solid? | Life

Who Said Physics Can’t Be Fun? These Lamar University students have a great time putting the theory of non-Newtonian fluids into practice.

In elementary classes, when we were little, they explained to us that matter comes in three states: solid, liquid or gaseous. Some elements, such as water, can pass from one to another, but not be two things at the same time. That is, water cannot be liquid and solid (ice) at the same time, for example.

But there is fluids that escape this definition. Or at least they try to fool us. Looks like liquid but supports a person’s weight. On the other hand, if you leave a spoon or a T-shirt on top, they sink.

The most curious thing is that these magical fluids are very easy to obtain. Anyone can make them at home, as we are going to see. But first, it’s worth taking a look at this fun video from the Fluid Mechanics class at Texas Lamar University, in the United States, to see how they work:

As we see in the video, it looks like a viscous liquid. When it is calm it behaves like a liquid and if you leave an object on it, it sinks slowly. But a person can walk on it without sinking, and even jump and dance, as if it were solid material.

Of course, there is nothing magical here. We are facing what is scientifically called a non-Newtonian fluid, namely, its viscosity does not respect Newton’s laws.

Most fluids, like water, have a constant viscosity. But these non-Newtonian fluids vary their viscosity depending on the temperature or, as in the case of the video, the constant tension that is applied (the weight).

The fluid that we see is very simple to make. We just need cornstarch, such as the classic Maizena sold in supermarkets, and Water. Two parts of water, one part of Maizena, and stir. The college kids in the video have added food coloring, to give it a little color.

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Although they are shocking, non-Newtonian fluids are quite common. They fall into this category, to a greater or lesser degree, everyday products such as toothpaste, butter, ketchup, or lava.

If you have children at home, the cornstarch experiment is very simple to do and they will surely find it funny. Of course, be careful because it is quite sticky …

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