What makes sand soft? – New York Times

What makes sand soft? - New York Times

What is the softest sand in the world? Why is some sand softer than others?

– Peter S., Brooklyn, NY

We do not know No one understands how sand works.

This may sound absurd, but it is absolutely true. Understanding the flow of granular substances such as sand is a major unresolved problem in physics.

If you build a clock tower and fill it with known grains of sand and sizes and shapes, there is no formula to say with certainty how long it will take for the sand to pass through the clock, or whether it will flow at all. Is. You just have to try.

Karen Daniel, a physicist at North Carolina State University who studies the content of sand and other grains – an area that is actually called “soft matter.” – told me that sand is challenging in part because grains have many different characteristics, such as size, shape, obesity and more: “One of the reasons we don’t have a general principle is that all of these properties are important.”

But understanding individual grains is just the beginning. “You have to be concerned not only with the properties of the particles, but also with the way they are organized,” said Dr. Daniel. Oose-packed grains can feel soft because they have space in their hands to flow around you, but when a single grain is tightly gathered, they do not have space to rearrange themselves to join your hands, which With them they feel determined. This is partly because the beach sand layers feel softer than the bottom layers: in the deeper layers the grains are pressed closer together.

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Our failure to find the general principle of sand is not lacking in effort. For everything from agricultural processing to landscape forecasting, it’s important to understand the flow of granules, and we’re not very good at it.

Dr. “People who work in chemical engineering factories handling particles can tell you that they spend a lot of time breaking down machines,” said Daniel. “Anyone who has tried to fix an automatic coffee grinder knows they get stuck all the time. These are things that don’t work very well. ”

Fortunately, we are not in the dark at all, and some things can be said about what makes sand soft or hard.

Round grain sand usually feels soft, as the grains pass through each other easily. Even small grains do not produce a pinprick feeling of individual grains pressing into your skin. But if the grains are too low, the moisture causes them to stick together, making the material feel complex and ripe.

Dr. Daniels said the softest material he ever softened was a substance called Q cell, a silica powder used to fill dents in surfboards. The powder coating is made of hollow grains, so it feels very light, and the silica material stays dry, which prevents it from biting. He likened it to a very nice, very dry beach with a bucket full of sand.

That beach cell A beach made of “sand” may be soft, but it will not be very pleasant. Good, dry powders are clay, not sand, and breathing them can be very dangerous for your lungs. The ideal beach sand will probably have a grain size and shape with balanced softness, dustiness, clamping and many other features that make the sand soft and good for walking. With so many individual factors to consider, it’s hard to say what the ideal soft beach sand would be.

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Raven Weber

About the author: Raven Weber

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