Double rainbows: Here's what they mean —

The physics blog Skulls in the Stars has answers to your rainbow-related questions. Among the fascinating things we learn here — each color in a rainbow represents the light reflected by a separate group of raindrops; skydivers can see circular rainbows; and the famous double rainbow happens when light bounces off the inside of a raindrop not just once ... but twice. — Maggie •

How to: Figure out what color dinosaurs really were —

Color is just a happy side effect of physics. So Canadian scientists are turning to The Canadian Light Source synchrotron, a particle accelerator in Saskatchewan, to help them figure out what color extinct duck-billed dinosaurs actually were. By putting a 70-million-year-old skull into the accelerator, they'll be able to figure out what molecules — from pigments to melanin-producing cells — are still present in the fossil. Francie Diep explains how it works at Popular Science. — Maggie •

Gloppy syrups gotta glop. Here's why. —

Honey, maple syrup, all those delicious gooey, gloppy things have some really interesting physics behind them, says Adam Becker at New Scientist. Viscosity alone can't explain the way strands of syrup stretch and drizzle as you pour them. Instead, when we see a difference between pouring honey and pouring water, what we're really seeing is the effects of tiny ripples in the honey. — Maggie •

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".

The physics of pull-ups —

Some people are naturally better than others at pulling off the elusive pull-up, writes Kyle Hill at Scientifica American. For them, it's all about mass-to-arm-length ratio — ideally, you want a low mass and short arms to minimize the amount of energy it takes to pull your body upwards. But Hill insists that the less genetically fortunate can learn to do pull-ups, too. It's just something that takes dedicated training. — Maggie •

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!

Impulse

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!

My boyfriend of 7 years and I are both physicists. Here's how he proposed to me. (imgur.com) (Thanks, Mark M!)

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.

Video: Throwing and catching an inverted pendulum – with quadrocopters | Robohub (Thanks, Kate!)

Inside a nuclear fusion research lab —

In downtown Cambridge, Mass., there's a research laboratory where scientists create plasma — the superheated, energy-dense gases that make up the Sun — and then try to manipulate that matter in ways that could, someday, be useful to the human race. Last week, the folks at The Physics Central Buzz Blog went inside this facility. Follow along on their virtual tour of a plasma physics lab. — Maggie •

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]

(via DVICE)

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.