Category: Uncategorized

Meteoric iron

Posted on by Brian Garthwaite
Meteor.
Big. Heavy.

Meteorites – those shooting stars which don’t completely burn up entering our atmosphere and then crash to the ground – can be made of all sorts of stuff. The most commonly found in museums and collections are metallic, not because they’re the most frequent type of meteorite, but because they’re the most likely both to survive entry/impact and to be discovered. A stony meteorite might look remarkably like an ordinary rock. A big chunk of warped iron just sitting on the ground? Slightly more conspicuous.

We have a few meteorites and pieces of meteorites on display, including this big slab. Cut, polished, and given an acid treatment, it shows off its internal crystalline structure. Primarily iron and nickel in two different crystalline shapes, it has a characteristic pattern known as a Widmanstätten pattern. Given a sufficiently long cooling period to enable crystal formation – typically on the order of millions of years – it produces this distinct appearance that highlights its extraterrestrial provenance.

Can’t do this stuff in a lab is what we’re saying.

The acid-etching process enhances the pattern where the high-nickel taenite alloy is more resistant to the acid than the low-nickel kamacite, turning a smooth, polished surface into one that looks, well, really cool.

Widmanstätten pattern
Shiny!

Inverted balloons

Posted on by Brian Garthwaite
Balloon on flask.
It’s like a hat.

What can you do with a large Erlenmeyer flask, a kettle of boiling water, and a bag of balloons? Science, of course!

Get the flask hot with a pour of boiling water first, then pour out. Add a small amount of boiling water – as hot as can be – and quickly seal with a balloon. We’re looking for steam, and lots of it.

Then wait and see what happens!

Balloon in flask.
Cool!

Spectrometer

Posted on by Brian Garthwaite
Spectrometer and sodium lamp.
Rainbows!

Astronomy is roughly 98% figuring out how to look at stuff better than our eyes can do it.

Gathering more light with large-aperture lenses and reflectors. Gathering more light with long camera exposures. Using detectors for light outside the visible spectrum, from radio waves to gamma rays. Launching telescopes a million miles into space to get away from our pesky atmosphere. Splitting the broadly blended colors we perceive into their component wavelengths.

That last one’s the easiest to accomplish in a student lab setting, and it’s a broadly useful scientific tool across many disciplines. Turns out that certain particular constraints caused by quantum physics make all sorts of other observations possible. Who knew?

Pictured above is a low-pressure sodium lamp, just like the ones that once illuminated nighttime streets around the world with their flattening orange glow. Looks orange to our eyes, but it’s primarily a mix of red, orange, and yellow wavelengths. If you measure those carefully enough, you can discern a certain “fingerprint” on a spectrum of light that would tell you if sodium is or isn’t present in what you’re observing.

Same applies to hydrogen and helium. Nitrogen and oxygen. Argon and neon. Carbon dioxide. Water. Every atom and molecule – including different ionized states, which is a particularly useful bit of information for astronomers – has its own unique spectrum of light it emits. You just need to look at it in the right way.

Even if it’s millions of light-years distant.

Fan carts

Posted on by Brian Garthwaite
Fan cart on track.
An object at rest.

Newton proposed three laws of motion, and it’s the second one that makes for the most interesting labs. Maybe there’s some way to make inertia both fun and educational, but let’s leave the first law for lecture. Equal and opposite reactions are pretty great, but that’s ideal for big demos. Read: rocket launches.

Force, though. Force lets students do stuff and observe what happens. Doing stuff and getting results is how you make physics more interesting.

One tool in our Newton’s-second-law arsenal is the fan cart. An assemblage of a cart with low-friction wheels and a simple DC motor holding a plastic fan. The fan mount pivots, providing variable direction of force. Runs on AA batteries, and is held together mostly with hot glue.

Two very good reasons for the hot glue: 1) When one of these invariably plummets to the floor, the less-than-rigid connections absorb a good deal of the impact when it all falls apart. Usually it falls into pieces, but nothing’s really broken. 2) After one has taken a tumble, it’s mere minutes to get it re-glued and running once more.

The reason for the fan is that it provides a close approximation of constant force, F. If F is constant, and mass (m) is constant, then by F = ma, acceleration (a) is constant, too. Give a running cart a little backwards push – an additional force – and study how its position and velocity change over time. Simple? Sure, and that’s helpful when tying together various concepts.

Relationships between force, mass, and acceleration according to Newton’s second law. Two-dimensional vectors come into play when rotating the fan. Our motion detectors read position, so it’s an illustration of integrals and derivatives underpinning the acceleration, velocity, and position of a moving cart.

The importance of catching a speeding object before it bangs into the end of the track and crashes to the floor.

Adapters

Posted on by Brian Garthwaite
Extruded aluminum telescope pier.
Expensive equipment goes on here.

A great many jobs in the daily work of a shop consist of riffs on this: can you make item A connect to item B? It might be physical connections, electronic and/or digital signals, or even the relatively abstract interpretation of transitioning a lab space over from one experiment to the next without disruption. The simplest ones are when someone can’t locate the proper connector cable. (There are so many different kinds!) Less simple are those times when two things are supposed to fit, but don’t.

Just straight-up don’t.

At the Tressler lab, we have the luxury of permanently-installed piers which support our telescope mounts. For our purposes, this is an excellent improvement over the default, a very stable yet heavy tripod. Now in the process of upgrading our mounts, we find that the tapped mounting holes on the pier don’t match the drilled and counterbored corresponding holes on the custom-made mount adapters. By 1/8″ or more in some cases. Sounds small. Is actually huge. Is will-not-fit-even-with-brute-force huge.

Note: not made in-house. We could try to guess where the error might have arisen, but our job is to fix it.

Also note: the previous mounting plate was not precisely machined to the proper dimensions, either, but was close enough that it was fastened by brute force. Sensing a theme here, which is this: precise measurements are crazy hard.

Pier with adapter plate.
Fix holes with more holes.

Getting to the adapter-for-the-adapter called for more than one CNC-milled plastic prototype. Measure, mill, test. Rinse, repeat. Polyethylene, as one might imagine, is cheap stuff.

A few test runs later, we have a custom-machined (in-house!) sheet of 1/2″ aluminum to connect to the 5/16″-18 tapped holes on the pier, which then sets up a new series of 1/4″-20 holes in this plate and the mount adapter to hold everything rock solid. Holes drilled and tapped, counterbored for a clean surface with all of those socket screws.

And all carefully measured and aligned on the milling machine to within 0.001″.

Telescope mount adapter, in place.
No one notices the unused holes in the dark.

You don’t appreciate the precision of reliable machinery and sharp tooling until the pieces slip together effortlessly. Whoa! Goosebumps!

Best part? The adapter is functionally invisible for anyone who doesn’t know to look for it. Few things feel as rewarding as solving a problem before (almost) anyone else realizes it’s there.

“The Perfect Cleaner”

Posted on by Brian Garthwaite
Capital Metal Polish can.
Buddy Brand!

Sometimes, stuff just lingers. It’s unclear how long it’s been sitting on this or any shelf, whether it has any use anymore, how on earth to dispose of it, etc. Of course, those odd objects tend to sport some of the coolest old labels.

So much to enjoy here! Buddy the dog, holding a flag with his name, but also helpfully labeled below as “Buddy,” just in case it wasn’t obvious enough. Directions for using metal polish on non-metallic surfaces, which – to be fair – might not be obvious. (Still mostly amounts to wipe on with a soft cloth, wipe off with a soft cloth.) The prime visual real estate for “Non-Inflammable,” which is an entertaining reminder of the flammable/inflammable quirk of the English language. What a country!

It’s not entirely clear if the yellow color was an original choice or has been caused by many years of aging paper.

Capital Metal Polish can back.
Seems pretty straightforward.

At any rate, the steel cap is thoroughly corroded shut, so there’s no telling what remains inside. Whether that corrosion is caused by or despite the contents of the Capital Metal Polish container, we’ll never know.

Colorful candy

Posted on by Brian Garthwaite
Box of bags of M&Ms.
Inside: milk chocolate, a statistics lesson, some artificial colors.

New concepts work better when there’s a hands-on element to engage students. It might be rockets, bouncy balls, lasers, or in the case of basic statistics concepts: candy. Specifically colorful candy. The physics labs have a long history of using M&Ms, though we hear that Skittles and Starbursts have their partisans, too. One bag for each student, TA, and instructor.

It’s a lot of milk chocolate.

The trick is that while each bag contains about the same number of M&Ms – there’s a statistics question all its own – they come in a range of different and unevenly distributed colors. How many blues are in your bag? Opening one won’t tell you much about how many to expect in another bag, but two might. Or thirty. Or three hundred. The more data you collect, the better you can understand the range of possible blue M&Ms and the likelihood of any particular value.

It’s very helpful in a variety of topics in physics and astronomy. It’ll show up later for those students who study radioactivity, which functions in a completely random fashion on an atom-by-atom level, not revealing its predictable patterns until you look at large populations. It’s critical for understanding uncertainty in measurements, because they’re never perfect. It’s foundational for techniques in astronomy used to separate out faint signals from distant celestial objects among the electromagnetic noise of the universe.

Plus they get to eat them when they’re done.

Blue M&M on the floor.
Included in the data set, or not?

Rockets

Posted on by Brian Garthwaite
Estes rocket.
Assembled. May or may not be recovered post-launch.

It’s nearly rocket day! Okay, well, it’s nearly time for a physics lecture on momentum conservation – good ol’ Newtonian mechanics – and nothing livens up a discussion of theory and mathematical modeling like making stuff shoot up into the sky. Or, quite possibly, fail to shoot up into the sky, but we’ve been running some advance tests and prepping backup plans because we really, really want things to go zoom.

Zoom, not boom. It’s much more of a hissing zzziiippp than anything else.

The demonstration usually shows three different rockets in succession, each more impressive than the last. The first one, a soda-bottle water rocket, actually illustrates the principle best. Pressurized water shoots out and down, so the rocket moves up. Mass, velocity, terrible aerodynamics. Occasional light spray, so keep your distance.

Then it’s off to model rocket land, with high-velocity solid fuel instead of water. Less mass but at a much, much higher velocity, and in no time that B-size engine has launched the little cardboard-and-plastic rocket high enough to be a speck that’s hard to discern. As long as the weather isn’t terrible, though, a standard B launch is not only recoverable, but entirely possible to catch before it reaches the ground, drifting lazily beneath its parachute.

Scaling on up to a C-size engine, we’ll have our final launch. Bigger engine, more momentum, and even the slightest breeze ensures it’ll drift far beyond our sight and ability to track. Anyone so lucky as to find the rocket afterward can keep it.

If it’s you, maybe stop on by and let us know?