Geoscientist Matt Kuchta explains why wet sand makes a better castle than dry sand — and what you can do to make your sand fortress even more impenetrable. Hint: The secret ingredient is window screens.
The other night, Joshua Foer posed this question was posed to a table full of science journalists. Most of us started talking about friction, and/or possibly something to do with the little flanges on either side of a train wheel.
We were all wrong.
This is a Richard Feynman video, yes, but it's more about mechanics than physics. Turns out, you can learn a lot about how trains stay on the track by looking under your own car.
Dry quicksand was a mythical substance — normal-looking sand that could swallow you in a flash. That is, until 2004, when scientists made the stuff in a lab. (Mark told you about that development.)
In this video, geologist Matt Kuchta explains how dry quicksand is different from both wet quicksand and stable sand. Hint: Think "Jenga".
There's a whole gallery of these eerie, psychedelic penguins at Wired, part of Nadia Drake's article about new research based on infrared thermal imaging. Strangely, researchers found that the exterior surface of the penguins was actually colder than the surrounding air. This, despite the fact that penguins maintain a fairly stable interior body temperature that's far warmer.
The researchers involved in the study think that discrepancy might be caused by an extreme form of radiative cooling. Basically, everything emits heat in the form of radiation. You, me, the Earth, penguins — we're all constantly losing heat as it radiates away from our surfaces. During the day, we get heat back from the Sun. At night, while there is some heat coming to us from space, it's much less. And on clear, windless nights — when there isn't a cloud clover to bounce our own heat back at us — we get even colder. As Drake points out, this theory doesn't totally work for the penguins. They were photographed on a pretty windy night. But it certainly produced some great images. Here's a link to the original paper, which you can read for free.
After a delay of too many years, Steven Gould has penned another Jumper novel. Impulse picks up where the excellent Reflex left off, with Davy and Millie -- a couple who possess the power to teleport -- living in exile, hiding away from the sadistic, power-hungry plutocrats who would enslave them and use them to increase their corrupt power.
But now Davy and Millie have an adolescent daughter, Cent (short for Millicent), and she's not happy living in an isolated cabin in the Yukon with a pair of teleports who are her only means of getting to civilization. Though there are some perks: when Mom and Dad take her shopping, it's as apt to be in Tokyo or Sydney as at the local Sears.
Cent's parents are understandably (over)protective of her. They've been hunted like animals, tortured, gassed, shot, by the conspiracy of wealth and privilege that would turn them into property. The last thing they want is for their daughter to be hunted too -- especially since Cent can't teleport.
And then she does. Once Cent comes into the family gift, things change. Her demand to be put into a regular school, to have friends, and a semblance of a normal life, is finally taken seriously by her parents. After all, if Cent doesn't get what she wants, she might just jump away and take it.
What proceeds is a book with the twin geniuses of Steven C Gould novels: first, a plot that roars along at 150mph without a pause for breath (I read Impulse over the course of about three hours, without a break); second, a fantastic, fresh, thoroughgoing explanation of the untapped possibilities of a old science fictional idea made new by an imaginative approach. As with the other Jumper books, Gould plays out the possibilities of teleportation with a combination of physics tutorials and spycraft that is absolutely enthralling.
Watching Cent get into (and out of) trouble, fall in love, battle bullies, and even intervene in humanitarian disasters is a pure delight. Gould shows us that with the right mixture of creativity and rigor, any idea can be spun out in a thousand fascinating ways.
This is a marvellous, if long overdue, installment in a series that I love to pieces. Now, if only Gould would return to his (equally wonderful) Seventh Sigma world!
Redditor bogus_wheel is a physicist in Sydney, Australia. Her boyfriend of seven years submitted a marriage proposal in the form of a physics paper that tracks their relationship (with a graph!). It is a beautiful piece of physics romance!
Ever see flying robots doing stuff that you never suspected flying robots could do? I have.
First, a state estimator was used to accurately predict the pendulum’s motion while in flight. Unlike the ball used in the group’s earlier demonstration of quadrocopter juggling, the pendulum’s drag properties depend on its orientation. This means, among other things, that a pendulum in free fall will move sideways if oriented at an angle. Since experiments showed that this effect was quite large for the pendulum used, an estimator including a drag model of the pendulum was developed. This was important to accurately estimate the pendulum’s catching position.
Another task of the estimator was to determine when the pendulum was in free flight and when it was in contact with a quadrocopter. This was important to switch the quadrocopter’s behavior from hovering to balancing the pendulum.
Second, a fast trajectory generator was needed to quickly move the catching quadrocopter to the estimated catching position.
Third, a learning algorithm was implemented to correct for deviations from the theoretical models for two key events: A first correction term was learnt for the desired catching point of the pendulum. This allowed to capture systematic model errors of the throwing quadrocopter’s trajectory and the pendulum’s flight. A second correction term was learnt for the catching quadrocopter’s position. This allowed to capture systematic model errors of the catching quadrocopter’s rapid movement to the catching position.
The finest moments in physics instruction always involves something going bang, blam, or boom, and this is no exception: Purdue's prof Mark French and grad students Craig Zehrung and Jim Stratton built a supersonic ping-pong-ball gun that attains supersonic muzzle velocity:
To demonstrate the conversion of subsonic to supersonic flow, Prof. French and his team designed the gun shown above. The end of the pressure vessel is sealed with laminating tape. Both the nozzle and the barrel are evacuated so the the gas flow is unobstructed. Overall, the gun is a bit less than 12 feet (3.65 m) in length.
To fire the gun, the pressure is increased in the pressure vessel until the tape breaks. French found that two layers of tape ruptured at about 60 psi (414 kPa), and three layers at about 90 psi (620 kPa). The speed of the ball was measured using a high-speed camera viewing the ball moving against a calibrated scale. A typical velocity was a bit over 1,448 km/h (900 mph) – nominally a velocity of Mach 1.23, which is about the top speed of the Soviet-era MIG-19 fighter.
The lead photo should convince the reader that this ping-pong gun is not a toy. The energy and momentum of the ping-pong ball is roughly the same as that of a .32 caliber ACP pistol – not the best choice for defense, to be sure, but quite lethal under the right circumstances.
Ping-pong gun fires balls at supersonic speeds [Gizmag/Brian Dodson]
This creepy-looking image of U.S. swimmer Tyler Clary has its origin in the movement of water molecules. The Fuck Yeah Fluid Dynamics tumblr explains what's going on — and how physics can make a swimmer look like a shiny, face-melted ghoul.
This happened in my friend's henhouse this morning.
My friend Kate Hastings, who took this photo, thinks this egg froze because the hen cracked it slightly. But it also looks like the kind of expansion cracking that you can get when eggs freeze and burst their own shells. When the water in the egg white and yolk freezes, it forms a crystalline structure — and that structure isn't very tightly packed. There's lots of space between the molecules, which means that solid ice takes up more space than the liquid it replaced. If the egg freezes solid enough, it's got nowhere left to expand except outside the shell.
Eggshells, as it turns out, are not a great insulator from the cold. Chicken butts are, but chickens also don't always sit on their eggs consistently enough to keep those eggs from freezing.
One side note: You can actually thaw and eat frozen eggs. But you shouldn't thaw and eat an egg like this. That's because the shell is actually a pretty good barrier against bacteria. If a fresh egg — the kind sitting under a hen — has cracked, there's a higher likelihood of bacterial infiltration.
Thanks to Kate and Grampaw!
They're the mullet of cold-protective clothing. Half glove, half mitten — really, fingerless gloves with a handy mitten flip-top.
They are also fantastic.
Now, partly, this is a matter of personal opinion. But partly, it's just good science.
Before you spend your weekend outdoors, or take your next chilly commute, let's talk briefly about glittens — and the science that makes them superior hand covering.
Read the rest
In today's XKCD What If?, Randall Monroe answers the question, "From what height would you need to drop a steak for it to be cooked when it hit the ground?" posed by Alex Lahey:
At supersonic and hypersonic speeds, a shockwave forms around the steak which helps protect it from the faster and faster winds. The exact characteristics of this shock front—and thus the mechanical stress on the steak—depend on how an uncooked 8 oz. filet tumbles at hypersonic speeds. I searched the literature, but was unable to find anything to help me estimate this.
For the sake of this simulation, I assume that at lower speeds some type of vortex shedding creates a flipping tumble, while at hypersonic speeds it’s squished into a semi-stable spheroid shape. However, this is little more than a wild guess. If anyone puts a steak in a hypersonic wind tunnel to get better data on this, please, send me the video.
If you drop the steak from 250 kilometers, things start to heat up. 250 kilometers puts us in the range of low earth orbit. However, the steak, since it’s dropped from a standstill, isn’t moving nearly as fast as an object re-entering from orbit.
I got to join in on a great conversation this morning on Minnesota Public Radio's "The Daily Circuit", all about the Higgs Boson and what it means for the future of physics.
This is a fascinating issue. Finding the Higgs Boson (if that is, indeed, what scientists have done) means that all the particles predicted by the Standard Model of physics have now been found. But that's not necessarily good news for physicists. For one thing, it would have been a lot more interesting to break the Standard Model than to uphold it. For another, we're now left with a model for the Universe that mostly works but still has some awkward holes — holes that it might be hard to get the funding to fill.
Daily Circuit host Kerry Miller, Harvard physics chair Melissa Franklin, and I spent 45 minutes talking about what is simultaneously a beautiful dream and a waking nightmare for the physics world. And I got to make a "Half Baked" reference in a conversation about particle physics, so you know it's a good time, too.
Listen to the whole conversation at Minnesota Public Radio's website.
Children’s literature is about the wonder of discovering new worlds, the power of imagination, and the all the little triumphs and defeats that make up a life.Read the rest
This is the difference between low kinetic energy (top) and high kinetic energy (bottom), as illustrated in the 1956 Disney book Our Friend the Atom. It may be useful in visualizing some of the ideas presented in my recent feature on space radiation.
From Fresh Photons, a fantastic blog chock full of science pictures.
Via David Ng
Absolute zero is supposed to be the coldest cold — 0 Kelvin, the point where atoms stop moving.
But researchers at the University of Munich say it's possible to get colder than that, an idea they've demonstrated experimentally. But what does it mean to be colder than cold? Here's the scientists' totally unhelpful explanation:
another way to look at these negative temperatures is to consider them hotter than infinity, researchers added.
Cool. Thanks, guys. Luckily, journalist Charles Q. Choi makes this strange idea make a whole lot more sense. Read his explanation at LiveScience.
On Being has a nice little archive of rare audio clips from Albert Einstein, speaking on various subjects, including what it means to be American, E=MC^2, Gandhi, and "The common language of science."
((Photo: Einstein sitting on the front steps of his home in Princeton, wearing his fuzzy slippers. Photo courtesy of Gillett Griffin.) )
Chalk this up under "Blogs You Ought to be Following". The Tumblr Fuck Yeah Fluid Dynamics is a great place to find succinct, clear explanations of the forces that make things flow. In particular, they're fantastic at posting explanations behind things you see in YouTube videos, both viral and obscure.
The video above — in which a nice Siberian guy tosses boiling water off his balcony and creates a cloud of snow — has been making the rounds recently. Here's how Fuck Yeah Fluid Dynamics explains it:
Several effects are going on here. The first thing to understand is how heat is transferred between objects or fluids of differing temperatures. The rate at which heat is transferred depends on the temperature difference between the air and the water; the larger that temperature difference is the faster heat is transferred. However, as that temperature difference decreases, so does the rate of heat transfer. So even though hot water will initially lose heat very quickly to its surroundings, water that is initially cold will still reach equilibrium with the cold air faster. Therefore, all things being equal, hot water does not freeze faster than cold water, as one might suspect from the video.
The key to the hot water’s fast-freeze here is not just the large temperature difference, though. It’s the fact that the water is being tossed ...