Shattered Backboard Glass and the Cat's Eye

"Dad, the basketball backboard is broken."

My 8-year-old son was looking out the back window. I was talking to a friend in our family room, and basketball was the last thing I was thinking about.

"No it's not," I thought as I stood up to investigate. This was August 2019. The backboard was only 2 years old. And that glass is 1/2-inch thick tempered-glass — and crazy heavy! The basketball stand was a splurge purchase when we bought the house in 2017 — over $2000 for a heavy-duty stand with a dunk-ready hoop (since I do so much dunking! haha) plus a net, and light. It's beautiful, really — kind-of a centerpiece in our back yard.

But at that price and age, there's no way it could be broken. Nobody had even been out there playing.

But I was wrong.

Wow, not just a little broken — shattered.

We immediately noticed that the break seemed to radiate out from a single point:

Another view:

Looks like something must've hit it.

(But what?)

---

I emailed the company. They were sympathetic, but they said it was clear that something had struck it, and the warranty didn't apply. They offered a replacement at a small discount.

Something was bothering the engineer in me, though.

I had looked around under the hoop for a rock or some other kind of projectile, and I hadn't found anything.

If the backboard had been struck by something small, like a bullet or a bb or a rock or something, I expected it would have shattered the impact site to powder, even if at a very small point. There was nothing like that.

If it had been struck by something large — a bird? hard throw with a basketball? a softball? — then I would've expected to find some marks on the surface of the glass, or the item itself. There was nothing.

I couldn't let it go.

---

A few Google searches, nothing useful.

I wrote a pretty long and piqued email to the company, trying to lay out the possible causes and how likely how unlikely it was that it had been struck based on the evidence, and how terrible an experience it would end up being if I had to replace it under those conditions...

But I didn't send that email. It just didn't sit right.

So I went back to Google.

This time, I found something — Nickel Sulfide in Tempered Glass Causes Spontaneous Fracture, by Thomas L. Pane, PE. Ah ha! Mr. Pane describes a case study of my *exact* situation, a pane of tempered glass shatters for no apparent reason.

Here's a comparison of the images, one from his site, and one from my backboard. Notice the distinctive "cat's eyes" pattern at the center of the fracture, two adjacent 6-sided shards.

A closer look shows the defect:

Turns out, it's a known issue in tempered glass manufacturing.* It's rare, and very hard to prevent or detect. Nickel sulfide is uniquely similar to water in that it's more dense when it is very hot, but as it cools, it wants to convert to a crystal form that is larger/less-dense. A tiny fleck of nickel sulfide in the glass is all it takes.

Tempered glass uses alternating layers of tension and compression to create huge internal pressures which makes the glass very strong. When the glass is first created the nickel sulfide has a hard time forming a crystal due to the high temperatures, and as the glass cools the nickel sulfide can't crystallize due to the high pressures. But once the glass is out in the sun, it can heat up enough to sometimes allow a corner of the nickel sulfide to crystallize. More hot/cold cycles allow the crystal to grow, until the internal pressures on the surrounding glass from the crystal are too high and the glass shatters.

Wow. That was awesome — such a thrill to have such a compelling explanation with hard evidence!

Armed with this info, I went back to the company and they offered to replace the backboard for free if I paid for shipping, which I agreed to, though a little reluctantly since shipping was over $100. Also, the backboard they sent was probably one that failed quality control, it had some discoloration on the lines, so I wasn't thrilled about that either. But I was happy to have my hoop back up and working.

I've kept the cat's eyes on my desk as a reminder of the experience:

Since then, I bought a digital microscope, and took a few pictures of the impurity:

Here's the top piece, zoomed to 1000x:

Here's the bottom piece at 40x:

And the bottom piece at 1000x:

It's interesting that both halves of the cat's eyes ended up with parts of the crystal.

Hope that helps someone out there.

---

* See also The Achille Heel of a Wonderful Material: Toughened Glass, an nice dive into the science, sources of nickel in the manufacturing process, etc.

Mariano Rivera's pitches

Impressive clip about Mariano Rivera's pitching.

I especially love the "here are the nearly 1300 pitches Rivera threw in 2009" part. Do they actually have tracks of every single pitch every pitcher throws? How do they get those tracks, I wonder?

Via DF, of course.

Medal Counts

Here's a fascinating look at Olympic medal counts over the years.

Just for fun, switch to the "by Ranking" tab, then step through the years from 1896 thru 1912 comparing the location of the games to who won the most medals. Coincidence? Also note who came out ahead in the 1936 Olympics in Berlin, under Hitler's watchful eye (see number 5 here).

Diving

So after watching a total of probably one hour of diving since the Olympics started this year, I can honestly say I still have no clue what the judges are scoring on. Every single dive looks perfect to me.

So the girl jumps, spins around like 10 times, then straightens up perfectly just in time to stab straight into the water like an arrow.

My first reaction is to cheer -- and hey, everybody else is cheering. How in the world do you get the timing right on something like that?! Amazing! But I resist, because I know I'm going to feel like an idiot when the lady announcer comes on and says, "Oh, she's going to be very disappointed with that dive."

Huh?

They need to have some sort of computer graphic that shows me how far twisted they on entry in degrees, how far apart their feet were and the pointing angle of their toes, and the volume of water that went up in the splash. "Oh, 0.5 degrees, 1/2 inch, 172 degrees, and 2.5 gallons? Not bad..." That's something an engineer/analyst can sink his teeth into!

I'm just going to start scoring them myself, and awarding gold medal flour cookies to the winners:


Hang in there, Guo, you still have a shot at the top cookie! Put a little more into the hair angle, lose the mysterious water, and you'll have it!

7th gold was close

Everyone thought that Cavic won that 7th race, but SI came out with some pictures that finally convinced us that Phelps won.

Interestingly, Phelps' head was definitely in front of Cavic's:



(picture snagged from SI website linked above)

So although Cavic's arms were out in front, his body wasn't, so I don't think he deserved the win either way.

Hopefully now that I've typed Cavic's name 5 times, I'll remember it at the 2012 Olympics. =)

8 for 8

Anybody not catch Phelps' last race? Amazing performance.*

Interestingly, wikipedia updates faster than pretty much any news site -- so for the scoop, try there first.

It's also amazing to me that I just watched the race 10 minutes ago, and yet I already can't remember who the 2nd place swimmers were. Fractions of a second behind our racers, stunning performers, yet I already forgot even which country they're from.

Or as Jerry Seinfeld says of the medal winners, "Gold --- Silver. Greatest guy in the world --- Never heard of him."

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* Did you catch the cool 3-d presentation on Michael's genetics that NBC was showing? In truth, Michael's a genetic anomaly when compared to average people -- his torso and arms are too long for his height, and his legs are too short, he's double jointed all over (including his ankles), and he wears size 14 shoes. I wonder how many hundredths of seconds advantage he gets from those things?

Gooberball finally hits the net!

Gooberball didn't last long on wikipedia, but now you can find the rules at the *official* gooberball homepage.

Stretching is a waste of time

Finally some proof for what every 12-year old boy always believed...

How to win at racquetball

Racquetball seems so easy -- all you have to do is hit the giant 20x20 foot wall in front of your face with the ball. Oh, and it's okay if it bounces of a few other walls in the process. But if you've ever been unable to score any points on a man whose only few hairs on his head were bright white, and who was unashamed to wear green-striped tube socks up to his knees, you know there's a little more to it.

Here's the secret that Old Ned knows all too well:

You know those shots that hit the front wall 2 inches off the floor in the corner? Those are called "kill shots", and if you can do that every time, you'll pretty much win every game.

Already knew that? Oh. Well then, most people can't hit shots that accurately (including me), so here are 6 shots that have a nice margin of error, and can be really tough to return -- each picture shows 2 different types of shots -- your opponent isn't pictured, but his location doesn't usually matter much for these shots. =)




Corners are always a good place to send the ball.

Any time you can bounce the ball off of both side walls in a single shot you're going to get some interesting effects from the spin (see the high-z and offensive splat shots above).

Also, unless you're playing with little kids, when you're in the middle of the court resist the temptation to hit the ball right in the middle of the front wall. Hit the side wall first, as low and hard as you feel comfortable so it'll still hit the front wall. These are generally much tougher to return.

You probably still won't beat Old Ned, but at least your other friends will get some exercise.