Why don't railroads need expansion joints?

The title of this video - which might change since I'm writing this up just a day after it was posted to YouTube - is a bit misleading. The actual question in the title - why don't railroads need expansion joints - is only answered in the last half minute or so of the video and is answered more thoroughly in a Practical Engineering video that I'll post after a jump.

The bulk of the video is spent explaining how railroad welds using thermite work. The video explains the nuances far better than other thermite videos I've posted before, explaining why the rails must be aligned and peaked, why the rails must be preheated (including a nice demonstration of heat treating), how the crystal structure changes as a result of the weld, and eventually why the rails don't need expansion joints.

This is the second of at least three thermite videos from Dr Derek. I thought I'd posted the first video to both blogs, but I can't seem to find it, so it'll likely show up next week.

St Louis Arch Final Construction and Thermal Expansion

I absolutely adore the St Louis arch - technically The Gateway Arch - and have been to the top at least a half dozen times. If I had my druthers, I would get to the top every time I'm in St Louis, but my wife and mother-in-law are less interested, so I merely admire it crossing the bridge each time we're in town.

One of our campers in Boise this summer explained that she had a lesson in her science class about the final topping-out ceremony of the arch, it being interesting because one side was in more direct sun. This lead to that sun side expanding more than the other, causing the two legs not to initially line up and the gap for the keystone to be too narrow if not for the hydraulic jacks installed to spread the legs apart.

Check out the details in the above video at 0:50 and in from the Arch's wikipedia article...

It was slated to be inserted at 10:00 a.m. local time but was done 30 minutes early because thermal expansion had constricted the 8.5-foot (2.6 m) gap at the top by 5 inches (13 cm). To mitigate this, workers used fire hoses to spray water on the surface of the south leg to cool it down and make it contract. The keystone was inserted in 13 minutes with only 6 inches (15 cm) remaining. For the next section, a hydraulic jack had to pry apart the legs six feet (1.8 m). The last section was left only 2.5 feet (0.76 m). By noon, the keystone was secured.

Brilliant, man. hose down the hot side with cold water. 

How cool is that?

I'm sorry...I know...it's a corny joke...but it was right there...I couldn't help myself...

How Does a Thermostst Work? (Mr. Wizard)

For those of us of a certain generation think back pretty fondly to Mr Wizard's World on Nickelodeon in the 1980's. Actually, quite a few generations think back fondly to Mr Wizard as Don Herbert started as Mr Wizard in 1951. He's even still being parodied on SNL.

This clip hits two things that we cover in matsci class at Princeton: thermal expansion (like the iron wire sagging) and the bimetallic strip.

In fact, the two wooden splints used to demonstrate the bimetallic strip at 2:00 is just about as brilliant a demonstration of that phenomenon as I've seen. Nicely done, Don.

The Story of Borosilicate Glass: Why Pyrex was Special

The narration in the above video is not done by a professional. The video would be way more enjoyable if it had been, but the content is high quality enough that I'm going to recommend watching it.

You have been warned.

The video is a narrated slide show (aka Powerpoint) explaining why borosilicate is a great material for glass that is going to be heated or cooled rapidly without shattering.

It does have corny jokes (the Mat Sci Aficionado cover, 'A Glass of Ice and Fire', for example) and some serious chemistry on the atomic scale (the Leonard-Jones scale, coordination numbers), but the video is worth a watch - for the teacher if not maybe for the student, at least not the students in the material science course at Princeton.

The video, by the way, is good enough that I'm going to check out what else The Mat Sci Guy has posted on his YouTube channel.

Unbreakable Ice Cream Safe - How to make cool stuff (I made a class!)

I warn you in advance that the actual material science content in the above video is contained very tightly between 0:33 and 2:14. The rest of the video is (at the beginning) an advertisement for a future video (the glitterbomb series is actually worth watching...begins as frivolous revenge and morphs into a serious examination of global criminal capitalism...but it's not about matsci) and (at the end) an advertisement for Rober's $249 online engineering class).

But that 0:33-2:14 shows a fun application of thermal expansion in which Rober built what he's calling an ice cream 'safe'. It's simply a metal sleeve and cap for an ice cream pint. The bottom of the sleeve is made of stainless steel, and the top is made of anodized aluminum. As Rober explains, the two fit together snugly at room temp, and the aluminum contracts 50% more at cold temperatures than does the stainless steel, locking the two parts together.

Simplicity itself, and a thing I would totally buy to demonstrate in my class...if only Rober would sell them.

I have searched the web for other, similar products thinking that somebody would have produced them, but I couldn't find one. Maybe the materials and machining precision make them cost-prohibitive.

If anybody comes across one of these for sale, could you send the info my way, please?

Glass bakeware that shatters (December 2010) | Consumer Reports

How have I missed posting this in the blog? I've been using this video for a couple of years to explain that pyrex =/= Pyrex.

I would explain, but honestly, the Consumer Reports host up there does a great job explaining that consumer pyrex isn't the same as lab Pyrex and hasn't been for decades.

Tl;dr - don't take your pyrex casserole dish from the freezer to the oven or from the oven to the countertop.

I make an ''8 Ball'' out of solid Stainless Steel and Brass

I'll admit that there's not a ton of content in today's video. Mostly it's a machining video where a guy - the unseen My Mechanics channel's youtuber - makes exactly what the video title says: an 8 ball made of stainless steel and brass.

The final product is pretty neat, and it would look good on a shelf as a curio - not really as much of anything else other than a heck of a thing to throw at someone or something you really hate.

I'm posting the video because of the neatness of the thermal expansion demonstrations at 1:50, 2:50, 3:30, and 4:10. In each case, a metal cylinder needs to be fit snugly into another metal cylinder. To get the fit to be a bit easier - but only temporarily - our host heats up the outer cylinder.

See, because metal - honestly, all materials - expand when heated. So the outer cylinder gets bigger as does its interior diameter. The youtuber is able to slip the inner cylinder inside, and when the outer cylinder cools, the fit becomes nearly seamless.

Brilliant stuff. 

Chicago Train Operator Sets Railway Lines on Fire

That's frickin' weird to see, man...

The news this morning reported that it was so cold in Chicago that the train operators were setting the tracks on fire with kerosene-soaked ropes.

I don't know that the exact details there are correct. The video below shows the operators in Alaska using a product call FireSnake. Their website says...

80M010 is based on a special alcohol blend modified with cellulose thickeners and enhanced with special fibers for maximum heat output. Upon combustion, the special fiber material used in this product releases nitrogen, water and carbon dioxide 

.... 

FireSnake® is a smokeless, easy to use, safe replacement for the old repair method of diesel rope.

So apparently the old version is diesel-soaked rope, and now there's a 'better' commercial product.

Either way, the issue that's relevant for us at hand is that metal contracts when it's cold. That means if it's cold enough, the train tracks will actually contract and separate from each other. To repair the lines, the workers need to first get the tracks to expand enough to join. Then they can do the repair.

Hot metal = expand...cold metal = contract/shrink

Why Bridges Move... (and more thermal expansion demos)

I wouldn't want to get my hands caught between those jaws on a hot day.

I don't know that I would actually show this video in class. The demonstrations of thermal expansion aren't all that impressive. The explanation and theory is solid, but the demos could be a little more impressive.

Like these, for example...

The Coolest Way to Open a Bottle of Wine

Yeah, that's one way to open a bottle of wine.

Shatter the glass, yeah.

It causes some secondary challenges (possible shards of glass in the wine, a messy lip of broken glass), all of which seem to have brought about solutions to those challenges.

As neat as the science is (hot glass contracts quickly and unevenly when cooled suddenly, aka thermal shock), the whole process just seems needlessly Rube Goldbergian to me.

Glass explosion at 343,000 FPS! - The Slow Mo Guys

38 degrees out in July in Texas? That doesn't seem all that hot to me.

Of course, I'm assuming that they're in Fahrenheit because I'm American. If the Slow Mo Guys are resolutely not going to use specific units, I'm going to assume whatever units I want.

This video, by the way, is brilliant.

The guys take kitchen-grade pyrex (really tempered soda lime glass not the lab-grade borosilicate glass) measuring cups and subject them to drastic thermal shock - propane torch then ice cold water. The real money shot happens at 5:38.

Then there's an outstanding comparison of the speed of glass shattering to human reaction time at 7:15. The glass shatters - spoiler alert - way faster than an eyelid can blink shut.

Then, at 8:30 we get an explanation of thermal shock and what's happening with the expansion/contraction dichotomy with the glass.

Edisto Island, South Carolina and Alexander Bache's

My wife and I took a trip to Edisto Island, South Carolina this June, camping a couple of miles from the beach in a rented, teardrop camper. The campsite adjoined Botany Bay, a plantation-cum-nature-preserve with gorgeous beach access.

In hiking Botany Bay's grounds, just past the Bleak Hall Ice House, we followed a sign for the Bache monument, neither of us having any idea what the Bache monument was - or how to pronounce Bache. After a fair number of twists, turns, spider webs, and uncertain left and right turns, we came upon a two and a half foot tall, four-sided, low-slope peaked granite monument inscribed with the name Bache and a few other things that meant nothing to us.

Heck, we didn't even take a photo, the monument was so uninteresting and unassuming.

Until we hiked through Edisto Beach State Park the next day, finding ourselves at the education center in the far, western edge of the park. There we found a second Bache monument, thankfully along with educational placards explaining just why that unassuming granite tower was remarkably important and interesting.

I'll start with the informational placards then follow up with my explanation and interpretation.

Compound Bars

The bimetallic strip is a tried and true demonstration of thermal expansion. It's available from all sorts of sellers (Flinn, Arbor Sci, bunches of other places). Invariably, though, the bimetallic strip (also known as a compound bar) is exactly the same from every seller. Yeah, the handle changes, but the metal strip is exactly the same - brassy on one side, silvery on the other, curving toward the brassy side.

This summer, though, I went searching to see if there were other bimetallic strips available, other combinations of metals to demonstrate.

It turns out that there are...sort of...

The four bars above are available from Arbor Scientific, but they come with a bit of a warning.

Of the three customer reviews on the Arbor Scientific page, one is pretty solidly and simply negative, "These pieces are just poorly made, and do not work at all. They are riveted together and tend to buckle instead of bend."

Yup, you can see clearly that those four compound bars are riveted together not smoothly joined as the more common bimetallic strip is. Clearly there's some reason why the cheap and omnipresent bimetallic strip is so omnipresent. It works. The two metals are - assumedly - easily and permanently joined.

Has anybody bought or used the four-bar set? If so, what are your experiences?

If anybody wants to see a couple of nice videos explaining the compound bar, check these...

Aluminum Thermal Explosion

And that, my friends, is why you always need to keep your mold totally, absolutely, perfectly dry when you're pouring molten metal. Steam explosions suck.

This is not something to laugh about...unless you're Russian, I guess.

Track Features - Flora, MS Derailment from Thermal Expansion Sun Kink

Sadly the video is all animation, but that's understandable considering the derailment mess that would have been created (see the video below).

If ever students ask why thermal expansion matters, here's a very clear example.

Fun Science Demos

Dr George Mehler (and ASM Foundation Board member) has worked with Jared Hottenstein and other Central Bucks science teachers have put together a series of science demonstration videos. The videos are geared mostly toward middle school science concepts, but a number of the concepts are ones that I know first hand that some high school students struggle with.

Most of them, admittedly, aren't material science concepts, but they are certainly basic science concepts that material science students would need to know. I'll post a couple of videos that are directly material-science-related (heat conduction and thermal expansion), but there a whole bunch more videos on their YouTube channel, FunScienceDemos. Check 'em out...

And a big thanks to George who came to our Montana camp to record some feedback from our campers for another project that he is working on, promoting the summer teacher camps.

How It's Made: Glass Christmas Ornaments

Much of this video isn't too big on the materials science focus - ooh, glitter being glued on - but the aspect of the glass ornaments not being cooled down too quickly so they don't shatter is a nice application of the thermal expansion of glass and how that can affect its strength.

Plus there's some great chemistry in the inside silvering of the ornaments.

How It's Made: the 2 Euro Coin

These two-euro coins are far more interesting than are the coins that we use in the United States. Yes, our coins are partially sandwiched, but we lack the two-part, ringed coins that are used in many countries in Europe. The rings just make the coins way cooler.

They also, of course, make the coins far trickier to manufacture, a process shown in depth in this video.