Discoveries in the Physics & Astronomy shop | Science, curiosities, and surprises
S’mores! Pretty much everyone likes s’mores, and they’re a great excuse to get outside and be social. And to make a cozy fire on an October evening.
Of course, if you also attempt to do this with physicists, the discussion is bound to turn to fluid turbulence and vortices and all of that…
In case you were wondering: there is a version of this which involves watching the fluid flow with lasers, because of course they have another way to play with lasers…
Considering that our course offerings cover the full range of classical mechanics, it should come as no surprise that we have many, many objects useful for demonstrating motion. Balls, cylinders, carts with low friction, blocks with high friction, carts which glide, carts which propel themselves, carts students can ride, etc. Also, just in case: a Jurassic Park-branded pickup truck.
It comes with a driver – currently leaning to their right, as if to call to someone on the passenger side of the vehicle – and a cage for the lion velociraptor. Complete with said velociraptor in the back.
In case you were wondering:
Yes, the parachute deployed.
No, we did not recover the rocket.
Both Physics and Astronomy courses do a lot of work with waves, and while light is one of the most important types for study, sound is exceptionally handy for demonstrations. There’s an immediacy, a feel, that can make sonic demos feel more intuitive.
We have a few of these about, metal bars with supports at the nodes of a standing wave, seated over a wooden box. The string goes where the bar doesn’t vibrate, and hence doesn’t dampen the sound, while the box helps it resonate louder. Ka-bong! They’re quite fun.
And, yes, Carl J. Ulrich of Minneapolis, Minnesota did some fine work here.
As one might imagine, hundreds of students in labs each semester means we use a lot of batteries. Just a ton of ’em.
Sometimes we need them at full capacity, but certain uses can be fine if they’ve started to develop some of that internal resistance after a while. Certain situations call for the higher potential current output of alkalines, while others need lithiums to keep the voltage from dropping too low. And at other times, the relative calm of a zinc-carbon battery is just perfect, like when students are building basic circuits and there’s a risk of shorting the batteries.
Much lower risk of booms and burns with the zinc-carbon.
Still, unless a battery’s in real rough shape, you never know how much juice they’ve got left just by looking. Pop one on the tester to see. When they’re almost new, you can hear the needle tap the far side!
This was a quality instrument, we’re supposing. Currently it’s a steel door, with its associated cabinet, apparatus, and everything else unaccounted for and presumed long gone. Any details associated with it have disappeared as well.
But check out that sticker! The Nuclear-Chicago Corporation made a variety of devices for nuclear radiation detection, although a cursory internet search reveals mostly hand-held items rather than cabinet-mounted equipment. Still, have a look through that fantastic mid-century aesthetic! Back in the days when uranium prospecting was what all the cool kids were doing.
They put out the model 2586 “Cutie Pie” in 1954. The Cutie Pie.
At any rate, Abbott Laboratories bought them out in 1964, so whatever device this accompanied goes back to sometime between 1954 – the name change to Nuclear-Chicago – and the 1964 sale. Should we ever stumble across the remains of it, rest assured we’ll make note of it.
Camping. For science!
The enormous beige box is a “Basecamp Kitchen Kit,” in case you’re wondering. It’s half as heavy as it looks.
Summer is progressing quickly, and it won’t be long before it’s toy kit time once more, including this multicolored assortment of silicone poppers! Available in different colors and sizes, over time you learn which ones pop the best.
Marbled performs better than solid colors.
Pink is often the best. A good one can nearly slap the ceiling from bench height.
No certainty as to why. But they sure are fun!
When you need to keep things cold, you have options, depending on your temperature needs and what’s available. Carnot cycle refrigeration is handy, effective, and reversible when you need to supply heat (think a heat pump or household refrigerator). You can use the thermoelectric effect via a Peltier device, in which electric current through dissimilar materials causes heat energy to flow in one direction. Or you can just huck a bunch of cold stuff at your target and wait for thermal equilibrium.
Cool running water is remarkably effective in this case. Even colder: ice, though a slurry of ice and water is often faster because of the increased convection and heat transfer through the cold liquid. Sometimes that sizable dollop of energy required for phase transition is really handy! Salt/ice/water slurry gets you colder still, and it’s a great way to make ice cream in the backyard.
Colder still: dry ice, or solid carbon dioxide. (We’re now at the point where you really don’t want this stuff to get on your bare skin.) It has some limited cooling potential, as it sublimates directly to gas at atmospheric pressure, and so good contact and heat transfer can be slow. You can get it to liquid form – the correct cold temperature range and high pressure – which is how we make dry ice when we need it. If you need a suitable liquid for extra-cold chilling, you’re probably looking at liquid nitrogen.
At -77°C, it’s very cold. Your chilling rate becomes limited by the Leidenfrost effect – that thing where a layer of insulating gas forms between the hot and cold materials, thermally and spatially separating them. Same thing happens when you dip a wet finger into a vat of molten lead, or the slippery skitter of a water droplet across the surface of griddle heated just right for pancakes. But, still, cold. Very cold. We use it as a backup for a freezer that’s supposed to hang out at -80°C as long as the power’s on. The stuff inside can handle slightly “warmer” temperatures for the time it takes to repair a power outage.
If you need even colder? Really dedicated folks dial it up to 11 and use liquid helium. That’s a whopping -269°C, which sounds intense. Or, if you prefer, about 4 K. It gets used here at the University, just not in Physics. (Astronomers might study it, but at the safe distances used for telescopic observation.)
All of these extra-cold normally-gases need special handling and care, not only for the temperature concerns, but also for what happens when they warm up and expand and displace all of the breathable air around. (Bad.) We all have some sense of the too-much-carbon-dioxide/monoxide symptoms – sluggishness, blue lips, etc. – but those of us not trained as fighter pilots aren’t as readily aware of the distinct symptoms of too much nitrogen, not enough oxygen. If you are one of the lucky few, you get to undergo normobaric hypoxia training, which can lead to roughly 18 seconds earlier awareness of hypoxia, which sounds like an awful lot in a plane that can travel a third of kilometer in that period at Mach 1.
As for the the dangerous effects of breathing a sudden roomful of now-gaseous helium? We assume your final words are hilariously high-pitched.
Behold: a box which counts! That’s it, for the most part. It counts pulses of positive voltage. Very quickly, and you can set some thresholds to tell it to count certain values but not others.
It also gates over an interval you set, so you can tell how many pulses it receives over, say, one second. It counts, displays the total, then counts again. Displays the new number.
We use these for our wave/particle duality lab experiment, which relies on counting individual photons. Yes, those. The teeny, massless quantum packets of energy, the messenger particles of electromagnetism. Light. It acts in non-intuitive ways, and the students who think “that’s amazing and I want more!” sometimes become Physics majors.
Part of using this box – just one aspect – is helping convince those students that only one photon at a time can be reaching the photomultiplier tube sensor. At the speed they move, a mind-boggling number of photons can zip through that meter-long box without bunching up. c in air isn’t all that far from c in a vacuum, so if your one-second counts aren’t remotely near 299,792,458 (adjusted for PMT sensitivity and other losses), you know some of those photons are pretty lonesome. Sometimes you need a little math to make sense of things you can’t directly sense.
One other fun aspect is a little switch hidden on the back: cricket. It’s the volume switch, letting the box emit a little beep for every pulse it counts.
If you’re counting pulses from a radioactive source, which arrive randomly, it can be informative to hear these irregular signals, gated and grouped into numbers which show a decaying curve.
If you’re counting 100,000 photons every second, in a room of other lab benches also counting thousands of photons? Less informative, more irritating.