Fun fact: the nerves in your skin don’t actually sense temperature; rather, they sense the flow of thermal energy. Metals below body temperature generally feel cold to the touch because they are very effective at conducting away thermal energy. Plastics at the same temperature feel warmer because they are much worse thermal conductors.
Category Archives: Physics
Roll Your Own
What’s next — self-assembling snowmen?
What the Nighttime Sky Really Looks Like
[C]onsider this impressive composite image of a wide region of the northern winter sky. With a total exposure time of 40 hours, the painstaking mosaic presents a nebula-rich expanse known as the Orion-Eridanus Superbubble above a house in suburban Boston, USA.
Mumbo, Meet Jumbo
Skulls in the Stars: Levitation and diamagnetism, or: LEAVE EARNSHAW ALONE!!!
It’s hard to tell if the author is being snarky or really looks upon mathematical physics as a “mumbojumbo” that impedes progress. Taking the statement at face value, it highlights an important and semi-common misunderstanding of many physics theorems, and so I thought I’d take a qualitative stab at explaining Earnshaw’s theorem and its relationship to diamagnetic materials and magnetic levitation.
Wet Shoe Problem — Check
The researchers calculated that shoes flick up about a pint of water after walking 20 kilometres on a damp day.
I wonder if the researchers really reported an imperial volume with a metric distance.
Rolling Followup
Last week I posted Rolling, Rolling, Rolling, with the video about the moment-of-inertia problem with the liquid-filled and ice-filled soda cans. Nick submitted the post to reddit (Thanks!), and I got a spike in traffic about 25x normal, for a day or so. That makes it (by far) my most popular post to date, and also the most popular home-grown post (I had gotten a spike or two from some interesting links I had posted).
One of the questions asked at reddit was what would happen if the ice was fee to move inside the can, so I tried that experiment — and there was no noticeable change. Even though the ice was riding on a layer of water it still spun up, and to the resolution of the video, the lag between the ice can and liquid can is the same. Water has pretty strong adhesion to a surface, and the entire interior surface of the can and exterior surface of the ice are interacting, so this shouldn’t be that surprising. Liquids, on the other hand, can be thought of as a very large number of layers (laminar flow), which gives much weaker coupling.
There are one or two other experiments I could run that require a sealable container, and so aren’t convenient with soda cans. I should be able to acquire some transparent sports bottles that should do the trick. If I can think of any comparisons that give non-intuitive results, I’ll post them.
Getting a Charge Out of Buckyballs
“Superionic” Buckyball Crystal
A team of researchers from Italy, Hungary, and the UK reasoned that buckyballs bonded into a crystal structure, like stacked fruit, would generate a material with big spaces in between the spheres. “To create large channels, we need large building blocks,” says team member Mauro Riccò of the University of Parma in Italy. And each buckyball can accommodate multiple negative charges, good for incorporating many positive ions. But which ion to use? Previous experiments found that sodium ions couldn’t move easily between the buckyballs.
The smaller lithium ion is a much better choice, Riccò and his colleagues report after completing a long characterization of their new compound, which consists of four lithium ions per buckyball.
No Volcanoes Here
Angle of Incidence = Music
Turn your sound up. Draw lines on the black screen to bounce the balls. Enjoy the music.
The Candy Cummings Effect
The fastball can’t get any faster, we’ve seen a changeup (slow light) and a knuckleball (aberration from atmospheric turbulence), so now High-Intensity Lasers Throw Scientists a Curve
OK, let’s start with the bad:
Researchers defy the laws of physics by making a laser beam bend
I really dislike that phrase, and whenever it’s used invariably the story goes on to explain how the phenomenon follows the laws of physics and it’s really just the researchers being clever in how they can manipulate one of the variables. As they did here — they reshaped the beam profile of the laser.
The researchers reshaped the profile of these pulses into that of an Airy beam using a thin plate of glass with a particular variation of thickness across the plate. “The phase shifts introduced by this plate turn the bullets from round in shape to the Airy beam that looks more like a triangle,” Polynkin says.
The beam ionizes the air along its path, which shifts the trajectory of the beam. Within limits.
Overall, the self-bending beam does have its limits—the bullets do not deviate from a straight line by more than the beam’s diameter. “If the beam is one centimeter [in diameter],” Polynkin says, “it won’t curve more than one centimeter.”
(Candy Cummings is the purported inventor of the curveball)