The science of invisibility cloaks

Something like Harry Potter’s invisibility cloak might actually be the best way to become invisible in real life. Unfortunately, it surely won’t be here for your next Christmas gifts, although scientists are trying (with some success) to understand how to make one.

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Spaghetti never break in two

If you grab a piece of spaghetti and bend it further and further, it will eventually break. It won’t just break in two, though: most likely it will break in three or more pieces. What sorcery is this?


Don’t believe me? Be a scientist: try it yourself!

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What is graphene?

Want to win a Nobel prize while discovering a material that’s cheap, transparent, flexible but resistent, and an astonishing electric conductor? Grab a pencil and a roll of adhesive tape. I’m serious.

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Phenomenal cosmic power, itty bitty living space

Wouldn’t it be great to take the universe in the lab? Astronomy is one of the most captivating parts of physics. I mean, one can’t scoff at the idea of unveiling the mysteries of the cosmos. Unfortuntely, galaxies and black holes don’t exactly cooperate as far as experimenting goes.

A group of physicists is working on a solution. Continue reading

How to make something clean itself

The secret of perpetually stainless stuff hid for centuries in plain sight—at least for those of us living around lotus leaves. Now physics can help you never to clean again, no matter what you spill.

It all comes down to how water sticks to stuff, in other words, how stuff gets wet. Continue reading

The thirsty dragon and other capillarity magic

The mighty thorny dragon. Credit: wikimedia

There once was a dragon, who lived in the desert and loved to eat ants. He liked it so much that he gave up the ability to drink for that: he made his mouth perfect for eating, but useless when it came to sipping.

Instead, he learned something way cooler: how to conjure water from sand itself, summoning a force even stronger than gravity.

It’s actually a true story: the thorny dragon is a majestic, 20cm long Australian lizard. A recent study revealed that, to drink, it uses a complicated network of narrow channels that start from its feet, suck water from the ground. Then, snaking between its scales, they deliver the water directly into the lizard’s throat.

We bottled that force into wondrous technologies such as… er… paper towels.

Seriously, though, paper towels do suck water against gravity. Since nothing is pushing the water up, that’s more or less sorcery. However, scientists prefer to call it capillarity, and it’s fascinating.

You probably noticed that water sticks to stuff. It’s scientifically called—I kid you not—wetting. But water also sticks to itself, and these two things combined make capillarity work.

In a way it’s like keeping up a hammock. The net is made to stay together, it’s suspended from the poles, and it sags in between under its own weight. In a tube with water it’s much the same: the tube walls act as many tiny poles around the water surface hammock.


Water in a capillary tube is like a hammock, but the poles around it grow a little on their own. credit: Stefanie Laubscher/pixabay

Water has an important difference from the hammock net: it self-sticks to the tube walls. That means it can climb (a little) up the wall. That’s why capillarity works so well in narrow channels, with walls close to each other. Basically, the distance between the “hammock poles” is small, so there’s less space for the net to sag.

A paper towel and its maze of narrow tubes under the microscope. credit: Mattheyses Lab/Emory University

Though it seems a little more mundane, paper towels work the same way. Inside their mesh hides an intricate network of tiny tubes through which water can climb. A little dragon magic in our kitchens.

If you want more
  • Water sticks to stuff because of van der Waals forces. They’re very cool, but they deserve their own thing.
  • Now that we know how to get stuff wet, can we do the opposite? Well, yes… stay tuned!!

Cover photo: CC0 Tom Mathews/pixabay

Why o why are rockets painted that way?

A few months ago, during a break at a conference, I met a very interesting young engineer. She told me she worked for Space X (you know, the Elon Musk ones, with the reusable rockets); particularly, in the team that takes care of painting the rockets. Our conversation was brief and left me wondering: do rockets need engineering teams just for the paint?

As it turns out, they always have.

In the old days, paint was used to keep an eye on the rocket’s roll (its spin around its length). Instruments on board don’t necessarily realize, amidst the phenomenal launch forces, the enormous acceleration, and the vibration.

Looking at how the large white and black checkered or striped patterns moved, you could check on it, just by looking, from the control center.

Different parts were also painted differently. Should any problem arise in flight, technicians could see in what part of the rocket it originated. Also, the rocket probably exploded as a result of the breakdown, so they only had a few seconds of grainy footage to go on. So they took any and all help.

Nowadays computer image analysis got much better (probably better than humans) and paint lost part of these functions. NASA still uses paint schemes at times, but most recent ESA and SpaceX rockets are just white.

A 2009 picture of a piece of NASA’s Ares. The Z-pattern is particularly useful to track roll. credit: NASA

Discovery launching, now you know why the tank is orange. credit: NASA, via commons

Why white? Because the rocketsĀ have to stand a long time in (hopefully) good weather in typically warm locations—like Florida. The white coat of paint keeps the frigid fuels from boiling off the tank. However, if it’s not strictly necessary, the tanks stay unpainted to save weight. It was the case, for example, of the iconic orange tanks for the shuttle.

When it’s used, paint must withstand being close to the freezing fuels, then the launch, then the rough conditions in space, and finally the extreme heat of reentry.

New materials must be designed for the job, and techniques must be developed to apply them so that they don’t shed or burn off.

That’s why, to paint a rocket, you needed—and still need—engineers, like the young lady I met.

If you want more
  • Wanna know more than you ever need on SpaceX? There’s a subreddit for that! It gave me many useful tips for this post
  • As for so many things space, NASA has a very interesting page about painting rockets too
  • Why should a rocket want to roll? Vintage Space explains that

Cover photo: CC0 kaboompics/