Category Archives: Physics
Physics is Everywhere
The distance between the metal bands holding the cylindrical structure together decreases from top to bottom because the pressure the water exerts increases with depth. The top band only needs to fight against the water at the very top of the tower but the bottom bands have to hold the entire volume from bursting out.
I Can Tell By the Look on Your Face, Man, You Want Something Even Bigger
Gallery of Fluid Motion
AIP Physics of Fluids: Gallery of Fluid Motion
This special section from Physics of Fluids features award-winning photographs and videos chosen from among numerous entries to the Annual Gallery of Fluid Motion exhibit, held at the annual meeting of the American Physical Society, Division of Fluid Dynamics.
These photographs and videos illustrate both experimental and numerical investigations of a wide variety of flow phenomena. Judged by a distinguished international panel of referees, winning entries were selected based upon criteria of scientific merit, originality, and artistry/aesthetic appeal.
Next Up: Quantum Sawing a Woman in Half
PFA
Ha Ha Ha HA Ha
What Woody Woodpecker Can Teach Us About Football
Kids always ask the best, most basic questions; they haven’t learned yet to pretend to be smart, to be ashamed of their ignorance; they’re just curious about how the world works. And the best scientists ask those kinds of questions too, which is why we might roll our eyes and chuckle a bit when we read about two California scientists who decided to delve into the underlying science of why it is that woodpeckers don’t get headaches.
Don't Take 'Any Colour You Like' Literally
If you were to put a lens, with a focal length 1/4 of the distance between the prisms, right in between the prisms, you’d definitely bring the light back to nearly a point at the first surface of the second prism. However, the angles of each color will not be what they need to be so that they’ll all come out parallel to each other out the second face.
How do I know this? Because I know what it takes to get all the colors to come out parallel (though not on top of each other).
Drs. Larry, Moe and Curly, I Presume?
Experimentalists Aren’t Idiots: The Neutrino Saga Continues*
Linking not just because Chad links to my post from yesterday but because he goes into more depth than the blurb I whipped up just before going to bed.
But since we’re on the topic, in case anyone is tempted to do yet another “I know the fundamental error you made” article: GPS clocks have their frequency adjusted to compensate for relativity — the clocks in space do keep nominal earth time already. On the ground, they would run slow by about 38 microseconds per day. In space, the gravitational shift is about 45 microseconds faster, opposed somewhat by the kinematic dilation of 7 microseconds. It’s not clear from my very quick scan if the authors of that paper had taken that into account or were trying to argue for some other effect.
Also, people do time transfer (i.e. synchronization) with GPS all the time. It’s called Common View GPS Time Transfer (though you can do it with any satellite that broadcasts). One might have gotten the impression that the neutrino experiment tried something novel to synch up their clocks.
*I am an experimentalist, and I am occasionally an idiot. Nobody is immune, really. But I have excellent colleagues who act as idiocy filters so at work, at least, any work that gets out to the public has been screened.
Cautionary Tale From Neutrinoland
There’s one main reason I don’t care how many non-experts rail against topics like we see with global warming or evolution. It’s because they are NOT EXPERTS. When you get into the details, science is subtle and tricky, and even though you might understand the big chunks, there comes a point where the non-expert — even a very intelligent one — will be out of his or her depth.
I offer up an example from the brouhaha of the month, the neutrino experiment. (I trust I don’t have to say no, not that one, the other one.) Followup: FTL neutrinos explained? Not so fast, folks.
There are two issues here. One is the paper itself on which Phil is commenting; the author seems to assume that the GPS satellite use for synchronization is always traveling in the same direction as it passes over the experiment, which I don’t think is the case. But I’m not a GPS expert. The second is that if this purported timing offset weren’t already accounted for in GPS receivers, it would show up as a positioning error. 1 nanosecond is 1 foot, roughly. (3 ns is a meter). So from just this one source we’re talking 10 – 11 meters of error. GPS does better than that. It’s kind of silly to assume that this wouldn’t be accounted for in setting up the system. So my initial reaction is that it’s bunk.
The second part is what Phil posts
I had thought of something like this as well. CERN and OPERA are at different latitudes, and since the Earth rotates, they are moving around the Earth’s axis at different speeds. Could that be it? I did the math, and the answer is no. Too bad; it would’ve been fun to be the person to have figured this out!
As I’ve mentioned at least once before, the rotation of the earth has no effect on clocks. The rotation causes deformation of the earth (we are oblate spheroid, mighty mighty oblate spheroid) and it turns out that the slowing from the kinematic time dilation is offset by a speedup cause by being slightly higher in the gravity well. So on the geoid, clocks all run at the same rate, and you only have to account for elevation changes.
It’s not surprising that an astronomer wouldn’t know that. Hell, I didn’t know that for the first few years I worked with clocks, and when I asked the question, the people I talked to weren’t sure why latitude corrections weren’t necessary. I went and found the answer in Neil Ashby’s “Relativity in the Global Positioning System”
Considering clocks at two different latitudes, the one further north will be closer to the earth’s center because of the flattening – it will therefore be more redshifted. However, it is also closer to the axis of rotation, and going more slowly, so it suffers less second-order Doppler shift. The earth’s oblateness gives rise to an important quadrupole correction. This combination of effects cancels exactly on the reference surface.
What does all this mean? Smart people outside of their field will not be familiar with subtle but very important effects. They may, as happened here, raise what seem to be legitimate objections that are well-know to people who actually work in the field.
Soon to be a Major Motion Picture
By golly, I wish I’d had this book as an undergrad.
As it was, I had to wait until this past January, at the ScienceOnline 2011 conference. These annual meetings in Durham, North Carolina feature scientists, journalists, teachers and students, all blurring the lines between one specialization and another, trying to figure out how the Internet can help us do and talk science. Lots of the attendees had books recently published or soon forthcoming, and the organizers arranged a drawing. We could each pick a book from the table, with all the books anonymized in brown paper wrapping. Greg “Dr. Skyskull” Gbur had brought fresh review copies of his textbook. Talking it over, we realized that if somebody who wasn’t a physics person got a mathematical methods textbook, they’d probably be sad. So, we went to the table and hefted the offerings until we found one which weighed enough to be full of equations, and everyone walked away happy.
The “we” includes me, because I scored a copy as well, and was in on the activity of sizing and weighing the anonymized books. There were probably more of these books than physicists (perhaps we can do better this year), though, so I imagine some species of biologist and/or journalist (statistically speaking) was disappointed.