YouTube // engineerguy
YouTube // engineerguy

The Brilliant Engineering of Disposable Diapers

YouTube // engineerguy
YouTube // engineerguy

Bill Hammack is The Engineer Guy on YouTube, where he explains the complexity behind everyday objects. Hammack is also a professor with a long track record in engineering work. As a communicator, he's able to bring out the wonder of engineering in even the simplest objects—and today's is the disposable diaper.

I'll be clear up front: There's nothing gross depicted in this video. It's classic "Let's pour some blue liquid on here" stuff. Hammack takes apart a typical disposable diaper and explains the complex technology in its various layers. I have never been so absorbed by a six-minute discussion of absorption (and repulsion) tech. Enjoy:

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What Happens When You Flush an Airplane Toilet?
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For millions of people, summer means an opportunity to hop on a plane and experience new and exciting sights, cultures, and food. It also means getting packed into a giant commercial aircraft and then wondering if you can make it to your next layover without submitting to the anxiety of using the onboard bathroom.

Roughly the size of an apartment pantry, these narrow facilities barely accommodate your outstretched knees; turbulence can make expelling waste a harrowing nightmare. Once you’ve successfully managed to complete the task and flush, what happens next?

Unlike our home toilets, planes can’t rely on water tanks to create passive suction to draw waste from the bowl. In addition to the expense of hauling hundreds of gallons of water, it’s impractical to leave standing water in an environment that shakes its contents like a snow globe. Originally, planes used an electronic pump system that moved waste along with a deodorizing liquid called Anotec. That method worked, but carrying the Anotec was undesirable for the same reasons as storing water: It raised fuel costs and added weight to the aircraft that could have been allocated for passengers. (Not surprisingly, airlines prefer to transport paying customers over blobs of poop.)

Beginning in the 1980s, planes used a pneumatic vacuum to suck liquids and solids down and away from the fixture. Once you hit the flush button, a valve at the bottom of the toilet opens, allowing the vacuum to siphon the contents out. (A nonstick coating similar to Teflon reduces the odds of any residue.) It travels to a storage tank near the back of the plane at high speeds, ready for ground crews to drain it once the airplane lands. The tank is then flushed out using a disinfectant.

If you’re also curious about timing your bathroom visit to avoid people waiting in line while you void, flight attendants say the best time to go is right after the captain turns off the seat belt sign and before drink service begins.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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Popcorn Might Be the Cheap, Biodegradable Robot Power Source of the Future
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If you've ever put a flat bag of kernels into the microwave and pulled out a full bag of fluffy popcorn two minutes later, you've witnessed a fascinating bit of food chemistry at work. Now, IEEE Spectrum reports that scientists are looking into applying the unique properties of popcorn to robotics.

For their study, presented at this year's IEEE International Conference on Robotics and Automation, Cornell scientists stuffed the movable parts of a robot (a.k.a. the actuators) with unpopped kernels of corn. Usually actuators are powered by air, hydraulics, or electric currents, but as the researchers found, popcorn works as a cheap single-use alternative.

When heat is applied to popcorn kernels, the water trapped inside them turns to steam, creating enough pressure to peel back the tough exterior and release the starchy endosperm. A sudden drop in pressure causes the endosperm to quickly expand, while the cool outside air solidifies it.

The results can be dramatic: When popping extra small white kernels, the cheapest popcorn tested, researchers saw them expand to 15.7 times their original size. Inside a soft robot, this amounts to building interior pressure that moves the actuator one way or another.

A similar effect can be achieved using air, and unlike popcorn, air can be pumped more than once. But popcorn does offer some big advantages: Using popcorn and heat is cheaper than building air pumps, plus popcorn is biodegradable. For that reason, the researchers present it as an option for robots that are designed to be used once and decompose in the environments they're left in.

You can get an idea of how a popcorn-powered robot works in the video below.

[h/t IEEE Spectrum]

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