Airplanes, Asparagus, and Mirrors, Oh My!

A love of Flying- upside down (photo by robshenk)

by Meghan D. Rosen

Last month, I asked you to submit a science-y question that you'd like to have answered in simple terms. You asked about light, and mirrors, and spices and space— I was delighted by the scope of the questions posed.

This month my fellow SciCom classmates tackled three. Steve Tung glides through the mechanics of flight; Beth Mole spouts off about asparagus pee; and Tanya Lewis reflects on mirrors.

Enjoy!

If you have more burning science questions, just post them in the comments. We'll be back next month with more answers.

And if you don't have a science question, but do have a thought or a picture to share, check out www.sharingamomentofscience.tumblr.com

How can an airplane fly upside down?

Daredevil pilots execute stunning aerobatic maneuvers― loops, rolls, spins, and more― sometimes while upside down for a long time. How do they do it? It might seem that the force keeping a right-side-up plane aloft would push a flipped plane down.

The trick is how the plane is angled in the air. Pilots can adjust the tilt to lift the plane, even when it is upside down.

You may have stuck your hand outside of a moving car and felt the rushing air push it up or down. Tilt your hand more, and that force is stronger. Turn your hand upside down and it still happens, though it might not be as powerful.

Plane wings, flipped or not, work the same way― tilt them up more, and air lifts the plane more. There are drawbacks and limitations, however. Higher angles cause more drag, slowing the plane. Tilt too far and the plane loses its aerodynamic properties and falls like a rock.

But not all airplanes can fly upside down. Some depend on gravity to fuel the engines; some would break under the different stresses of flying inverted. Stunt airplanes use specially designed wings, bodies, and engines to be more agile, more durable, and more versatile.

Steve Tung once dreamed of designing airplanes and rockets. He now dreams of pithy, memorable prose. (He received a bachelor's degree in mechanical engineering with a concentration in fluid mechanics from Cornell University) Twitter: @SteveTungWrites

Many years ago Mel Brooks asked the one question which had haunted him all these years: “Why, after I eat a few stalks of asparagus, does my pee pee smell so funny?”

It wasn’t until recently that scientists started to unravel this odorous riddle. The answer lies with both the whizzer and the whiffer.

When we digest asparagus, its sulfur-containing compounds can break down into stinky subunits that strike as early as 15 minutes after eating. Although the culprit behind the smelly bathroom visits hasn’t been caught, the most likely suspect is methanethiol.

But in bathroom exit surveys, only some asparagus eaters say they can smell the excreted evidence.

In 2010, scientists went digging through a database that linked genetic data with survey data including answers to questions like ‘Have you ever noticed that your pee smells funny after you eat asparagus?’

They found that people who have particular DNA changes around a set of genes responsible for olfactory receptors—molecular smell detectors in your nose—are more likely to be able to smell asparagus pee.

So for those that can’t smell asparagus pee, it might not mean that you can’t make it.

Last year a different set of scientists waved pee vials under people’s snouts to sniff out who could make asparagus pee and who could smell it.

They confirmed that some schnozzles can’t smell asparagus evidence. But they also found that some people don’t seem to make it either, at least not in detectable amounts.

Since scientists haven’t pinned down the stinky subunit responsible, they can’t say for certain if it’s not there at all or just at really low levels that we can’t smell.

For now, it seems likely that our abilities to make and smell asparagus pee probably exist on sliding scales, and whether or not you can smell it seems unrelated to whether or not you can make it—so, continue to ponder in the potty.

BethMarieMole
Beth Mole earned her PhD in microbiology at UNC Chapel Hill studying a potato pathogen and did postdoctoral research on antibiotic resistant bugs at UNC's Eshelman School of Pharmacy. She started writing about science in 2008 for Endeavors magazine and is currently enrolled in the science communication program at UC Santa Cruz.

Why does a mirror reverse left-right but not up-down?

When you look in the mirror and point your right arm out to the side, your reflection in the mirror points its left arm. But when you point up above your head, your reflection doesn’t point to its feet. Even if you lie on your side and point your arm out, the mirror seems to “know” to switch which arm your reflection points, even though that’s now up or down relative to the ground.

What’s going on? Actually, mirrors don’t reverse things left-and-right, they reverse them in-and-out. Imagine casting a rubber mold of yourself, then turning the mold inside-out. Your reflection would face you, but your arms would appear to switch sides.

Another way to think about it is this: write something on a piece of semi-transparent paper and hold it up to the mirror. The reflected writing is, of course, a mirror image. But now turn the paper around so the writing faces you, and look at the reflection in the mirror. The writing is the right way round again. The reflection is like a stamp, making a “light print” of the writing on the page.

Tanya Lewis

Tanya is a graduate student in the science communication program at UC Santa Cruz. She is an incurable science geek with a penchant for storytelling. She can be reached at tanlewis (at) gmail (dot) com or on twitter @tanyalewis314

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