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6 Unconventional Uses for the Tennis Ball

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Wimbledon is upon us! And the oldest tennis tournament on the planet has put a hot spotlight on the sport's best and brightest. And by best and brightest, we don't mean the athletes.

We're talking about those fabulously fluorescent felted orbs whose satisfying pops and whirrs keep audiences enthralled for the two weeks of tournament play. But what happens to those tennis balls after the champion is crowned and athletes and fans alike start looking toward Queens and the next Grand Slam?

Much like aging tennis champs, they too must retire when they lose their bounce—that is, when they are no longer able to rebound the regulation height of 53 to 58 inches when dropped from a vertical distance of 100 inches. (At Grand Slam matches like Wimbledon, tennis balls are usually replaced every seven to nine games.) According to the International Tennis Federation, an estimated 360 million tennis balls are produced every year—which, if lined up ball-to-ball, could cover the distance between Wimbledon and Flushing Meadows four times over. That's a lot of pressurized rubber and felt.

But the golden years of these numerous tennis balls can be filled with purpose. Here are six lesser-known, unconventional, off-court uses for a tennis ball.

1. Sleep Aid

Have a light snoring problem? Tape or otherwise affix a tennis ball to the back of your pajamas before you go to sleep at night. The idea is that it will keep you from rolling onto your back mid-slumber, lowering the chances of snoring and raising the chances of a better night's sleep. Sleep researchers have found that sleeping on one's side does reduce snoring, but a Journal of Clinical Sleep study in 2009 concluded that most people think this trick is uncomfortable and give up on it.

2. Mouse House

If you bore a small, mouse-sized hole in a tennis ball, it can make a great safe haven for species of rodents like Eurasian harvest mice. In 2001, the All England Lawn and Tennis club donated used Wimbledon balls to a wildlife trust in the UK to use as protective homes and breeding nests for the endangered mice population.

3. Housekeeper

Felt is a great material for dusting, because the thick woolen fibers cling well to dust and cobwebs. So why not get rid of those pesky, hard-to-reach dust and cobwebs by throwing a tennis ball at the problem? A tennis ball is also very effective at removing scuff marks from surfaces like hardwood and vinyl. A popular DIY scuff cleaning tool involves slicing an X into a tennis ball with a razor blade and affixing it to the end of a broomstick.

4. Laundry Mate

This is another popular DIY housecleaning trick. Throw a tennis ball into the dryer with your down comforters, pillows, towels and other fluffy and puffy linens. The tumbling balls keep your wet linens from clumping up and losing shape as they dry. It functions in the same way as a dryer ball, manufactured for that specific purpose.

5. Physical Therapist

Many physical therapists recommend using a tennis ball to work the kinks out of tight muscles or soothe muscle aches, as the pressure created by sandwiching a tennis ball between your muscle and a wall or floor is good for targeting the tension-sources or “trigger points” that cause muscle distress. The spine and legs are common spots for tennis ball “therapy.” Some physical therapists also recommend using them as substitutes for free weights (cutting one open and filling it with sand can add more weight), and as grip strengtheners.

6. Slug Trapper

Next time you have a backyard boozefest, pour one for your homies. A little beer in the garden may help keep your slug problem at bay. Apparently, the enemy No. 1 of gardeners the world over has a weakness for a good brewski (they're attracted to the fermented yeast), and many gardening resources recommend setting up beer-filled slug traps throughout the garden to catch them. Using a tennis ball cut in half is often suggested as a DIY option.

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iStock // Ekaterina Minaeva
Man Buys Two Metric Tons of LEGO Bricks; Sorts Them Via Machine Learning
May 21, 2017
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iStock // Ekaterina Minaeva

Jacques Mattheij made a small, but awesome, mistake. He went on eBay one evening and bid on a bunch of bulk LEGO brick auctions, then went to sleep. Upon waking, he discovered that he was the high bidder on many, and was now the proud owner of two tons of LEGO bricks. (This is about 4400 pounds.) He wrote, "[L]esson 1: if you win almost all bids you are bidding too high."

Mattheij had noticed that bulk, unsorted bricks sell for something like €10/kilogram, whereas sets are roughly €40/kg and rare parts go for up to €100/kg. Much of the value of the bricks is in their sorting. If he could reduce the entropy of these bins of unsorted bricks, he could make a tidy profit. While many people do this work by hand, the problem is enormous—just the kind of challenge for a computer. Mattheij writes:

There are 38000+ shapes and there are 100+ possible shades of color (you can roughly tell how old someone is by asking them what lego colors they remember from their youth).

In the following months, Mattheij built a proof-of-concept sorting system using, of course, LEGO. He broke the problem down into a series of sub-problems (including "feeding LEGO reliably from a hopper is surprisingly hard," one of those facts of nature that will stymie even the best system design). After tinkering with the prototype at length, he expanded the system to a surprisingly complex system of conveyer belts (powered by a home treadmill), various pieces of cabinetry, and "copious quantities of crazy glue."

Here's a video showing the current system running at low speed:

The key part of the system was running the bricks past a camera paired with a computer running a neural net-based image classifier. That allows the computer (when sufficiently trained on brick images) to recognize bricks and thus categorize them by color, shape, or other parameters. Remember that as bricks pass by, they can be in any orientation, can be dirty, can even be stuck to other pieces. So having a flexible software system is key to recognizing—in a fraction of a second—what a given brick is, in order to sort it out. When a match is found, a jet of compressed air pops the piece off the conveyer belt and into a waiting bin.

After much experimentation, Mattheij rewrote the software (several times in fact) to accomplish a variety of basic tasks. At its core, the system takes images from a webcam and feeds them to a neural network to do the classification. Of course, the neural net needs to be "trained" by showing it lots of images, and telling it what those images represent. Mattheij's breakthrough was allowing the machine to effectively train itself, with guidance: Running pieces through allows the system to take its own photos, make a guess, and build on that guess. As long as Mattheij corrects the incorrect guesses, he ends up with a decent (and self-reinforcing) corpus of training data. As the machine continues running, it can rack up more training, allowing it to recognize a broad variety of pieces on the fly.

Here's another video, focusing on how the pieces move on conveyer belts (running at slow speed so puny humans can follow). You can also see the air jets in action:

In an email interview, Mattheij told Mental Floss that the system currently sorts LEGO bricks into more than 50 categories. It can also be run in a color-sorting mode to bin the parts across 12 color groups. (Thus at present you'd likely do a two-pass sort on the bricks: once for shape, then a separate pass for color.) He continues to refine the system, with a focus on making its recognition abilities faster. At some point down the line, he plans to make the software portion open source. You're on your own as far as building conveyer belts, bins, and so forth.

Check out Mattheij's writeup in two parts for more information. It starts with an overview of the story, followed up with a deep dive on the software. He's also tweeting about the project (among other things). And if you look around a bit, you'll find bulk LEGO brick auctions online—it's definitely a thing!

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Name the Author Based on the Character
May 23, 2017
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