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.

Making an atomic trampoline

I'll admit that I entered the giveaway to hopefully win one of NileRed's atomic trampolines.

No luck, though, so I'll only be able to show the video.

An atomic trampoline is really high on my matsci wish list, though. I want one so desperately.

I certainly watched this NileRed video and came to the conclusion that I'm a lot of money and skills away from making one myself.

How Disc Golf Discs Are Made (MVP Manufacturing Tour) - Smarter Every Day 301

Summer of George!

I do want Destin to get back to making shorter videos like his initial, six-and-a-half-minute Prince Rupert's drops video, but I understand that he's just working to optimize for the algorithm. 

At least the Smarter Every Day videos are quality videos from tip to tail, showing brilliant views and asking questions along the way of the entire manufacturing process.

I learn so much from all of Destin's videos.

And I'm going to get myself some of those MVP discs. 

What does it mean to be a metallographer?

Sprechen sie deutsch?

Ja, aber nur ein bisschen.

In case you don't speak German, the ZEISS folks have provided handy captions so Toni can take us on a bit of a tour to show what a metallographer does.

I will say that there are some metallographers in the world who don't necessarily use exclusively ZEISS microscopes, though, in spite of what this video shows.

How This 300-Year-Old Pastel Stick Maker Creates Nearly 2,000 Colors — More Than Its Competitors

#forbiddenfrosting

Most hand manufacturing processes are stunning to watch, and in this case it apparently produces a product that is superior to mass manufactured competitors. It has to be way more expensive and time-consuming, though.

So pretty...so mesmerizing...so colorful...

The worry about black plastic...and a correction

This video was published by Adam Ragusea in November 2024 about a study from a month or so earlier than that. 

The tl;dr of the study is that many black plastics are produced from recycled black plastics that are frequently sourced from electronic waste which contains higher amounts of particularly toxic, flame-retardant chemicals. Those 'new' black plastic items could - especially if used in high heat areas like food flippers and turners on the stovetop - release higher than safe amounts of those chemicals.

In the above video, Adam goes through the possible concerns that this raises as well as noting a possible math error in the study's calculations suggesting that the level of concern is slightly lower than the authors might have initially suggested.

The article was corrected - noting exactly the math error that Adam suggested, and Adam published a spectacular video explaining why that error should not undermine faith in the scientific process or even in the researchers and authors of the original article.