Category Archives: Physics

The Costanza Effect

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Scientists Confirm Existence of Moon

I think this is pretty cool. Calibrating a detector by basically doing the opposite of how you would normally calibrate an instrument.

It’s important in this game to make sure your detector is really “pointing” where you think it is. (Ice Cube doesn’t move, of course; the detectors find tracks in the ice, from which a direction is reconstructed.) So it would be nice to have a source of muons to check against. Sadly, there is no such source in the sky. Happily, there is an anti-source — the shadow of the Moon.

Being Wet Can Be Cool(ing)

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How Do Things Cool With Evaporation?

You know water evaporates – that’s when it turns from a liquid to a gas. You probably also know that a hot pot of water will cool off in part because of evaporation. However, did you know that a cup of water at room temperature will also cool off? Yes, even if the water starts at room temperature it will cool off to below room temperature. I think this is awesome.

But how does this work?

Poe, Poe, Pitiful me

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10 physics misconceptions, explained poorly

[This blog post was written by a guest columnist, a D-student in freshman physics who will remain anonymous]

It’s pretty obvious it’s not, even accounting for Poe’s law (as applied in this case, one could not tell the difference between a D- student and a professor pretending to be a D- student, were the professor able to avoid succumbing to snark. Or hyping his book.). The misconceptions are very real, though. One of my favorites, much more plausibly true, is the one about heavy boots.

In my teaching days I saw plenty of these. So much so that we once played a game of “GCE Jeopardy!” at a party my housemates and I threw. The answer was given, and one had to name the Gross Conceptual Error (GCE) that would have elicited the response. For example, if the answer in the “mechanics” topic was “It is always conserved”, the proper GCE question would not be energy, since that’s actually conserved. It would be “what is momentum?” Some students would invariably insist that momentum was always conserved, even in the cases where a net force was acting. Which counts as a gross conceptual error.

Those Were the Days

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Good Old-Fashioned Technology

I don’t want to over-state the case because, actually, I love new gizmos that allow me to browse my music collection through my TV and to photograph the Orion Nebula in mere moments using the unbelievably sensitive ISO25600 setting on my camera. I wouldn’t want to halt the inevitable march of progress even if I could. But I would like to take this opportunity to mark the passing of some dearly loved and enlightening technology that has gone the way of all flesh.

I agree. New technology is amazing , but there’s something to be said about the older analog equipment, where you could tinker in ways that you can’t do anymore.

A New Species of SQUID

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Viewpoint: A SQUID Analog with a Bose-Einstein Condensate

How can an ultracold gas act like a dc-SQUID? The Josephson effect relies on the sinusoidal nature of the relation between the current that flows and the relative phase that exists across the junction. In conventional dc-SQUIDs the flow is an electric current, whereas in BECs it is a mass current, and the relative phase is the difference in phase factors of the wave function on either side of the junction. In these macroscopic quantum systems, the relative phase evolves in time in response to the applied potential differences (voltage difference for superconductors, pressure and temperature differences for superfluid helium, and population difference between the two condensates for BECs). A constant potential difference, for example, leads to a relative phase that increases linearly in time, and through the sinusoidal current-phase relation, this then gives rise to an oscillating current. The nonlinear current-phase relation is a key signature of the leakage and the weak coupling of the two macroscopic wave functions.