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Plane vs. Conveyer Belt: Hell Yeah the Plane Takes Off

UPDATE: Well, that'll teach me to blog about physics I don't fully understand! I have researched the issue and edited the post below, now that I understand the explanation from The Straight Dope.

Last night the Discovery show Mythbusters settled a longstanding debate: whether an airplane on a conveyor belt (running in the opposite direction as the plane) can take off. The short answer, as liveblogged by Jason Kottke:

HELL YEAH THE PLANE TAKES OFF

It's a curious problem. As a thought experiment, it seems (at least to me) like the plane shouldn't take off, since it wouldn't gain takeoff velocity relative to the ground. But according to, you know, SCIENCE, the plane will still reach takeoff velocity -- the wheels will just spin twice as fast. This is because the wheels aren't providing any thrust, it's the engines (propellors) that are pulling the plane forward through the air. It's the velocity of the air relative to the wings that counts, which is generated by the action of the engines pulling the plane forward. So the conveyor belt will only stop the plane from gaining takeoff velocity if it creates enough friction to counteract the forward thrust of the engines (or propellor).

Despite explanations of this sort by physicists, the issue wasn't really settled until last night's Mythbusters episode -- they replicated the experiment on a small scale, then with a real airplane (albeit an ultralight), using a huge tarp dragged by a truck as the "conveyor belt." Even the plane's pilot thought the plane wouldn't overcome the power of the conveyor belt, and thus wouldn't gain takeoff velocity. When Jason Kottke first blogged about the issue last February, his comment thread was hot with controversy. So Kottke tuned in to Mythbusters last night and liveblogged the event, with results visible above. His exuberance over the plane's liftoff has resulted in a "HELL YEAH THE PLANE TAKES OFF" tee-shirt available starting at $18. Wow.

Watch the Mythbusters clip in question below.... (Note: if this clip is pulled down, I'll try to dig up another.)

Keep in mind that the issue here is partly semantic, and has to do with how you explain the theoretical problem. I explained it poorly in my first post, since I (like apparently many) assumed that air would flow over the wings as a result of the propellor spinning, and that would be enough to make the plane take off, even if it was stationary. This is not the case -- the plane is going to need to move air over its wings in order to take off. The point of the experiment is simply that yes, the plane will move despite the conveyer belt underneath it. And that movement (at least in this experiment) provided sufficient lift to get the plane off the ground.

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science
What Pop Culture Gets Wrong About Dissociative Identity Disorder
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From the characters in Fight Club to Dr. Jekyll and Mr. Hyde, popular culture is filled with "split" personalities. These dramatic figures might be entertaining, but they're rarely (if ever) scientifically accurate, SciShow Psych's Hank Green explains in the channel's latest video. Most representations contribute to a collective misunderstanding of dissociative identity disorder, or DID, which was once known as multiple personality disorder.

Experts often disagree about DID's diagnostic criteria, what causes it, and in some cases, whether it exists at all. Many, however, agree that people with DID don't have multiple figures living inside their heads, all clamoring to take over their body at a moment's notice. Those with DID do have fragmented personalities, which can cause lapses of memory, psychological distress, and impaired daily function, among other side effects.

Learn more about DID (and what the media gets wrong about mental illness) by watching the video below.

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History
Scientists Reveal Long-Hidden Text in Alexander Hamilton Letter
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Age, deterioration, and water damage are just a few of the reasons historians can be short on information that was once readily available on paper. Sometimes, it’s simply a case of missing pages. Other times, researchers can see “lost” text right under their noses.

One example: a letter written by Alexander Hamilton to his future wife, Elizabeth Schuyler, on September 6, 1780. On the surface, it looked very much like a rant about a Revolutionary War skirmish in Camden, South Carolina. But Hamilton scholars were excited by the 14 lines of writing in the first paragraph that had been crossed out. If they could be read, they might reveal some new dimension to one of the better-known Founding Fathers.

Using the practice of multispectral imaging—sometimes called hyperspectral imaging—conservationists at the Library of Congress were recently able to shine a new light on what someone had attempted to scrub out. In multispectral imaging, different wavelengths of light are “bounced” off the paper to reveal (or hide) different ink pigments. By examining a document through these different wavelengths, investigators can tune in to faded or obscured handwriting and make it visible to the naked eye.

A hyperspectral image of Alexander Hamilton's handwriting
Hyperspectral imaging of Hamilton's handwriting, from being obscured (top) to isolated and revealed (bottom).
Library of Congress

The text revealed a more emotional and romantic side to Hamilton, who had used the lines to woo Elizabeth. Technicians uncovered most of what he had written, with words in brackets still obscured and inferred:

Do you know my sensations when I see the
sweet characters from your hand? Yes you do,
by comparing [them] with your [own]
for my Betsey [loves] me and is [acquainted]
with all the joys of fondness. [Would] you
[exchange] them my dear for any other worthy
blessings? Is there any thing you would put
in competition[,] with one glowing [kiss] of
[unreadable], anticipate the delights we [unreadable]
in the unrestrained intercourses of wedded love,
and bet your heart joins mine in [fervent]
[wishes] to heaven that [all obstacles] and [interruptions]
May [be] speedily [removed].

Hamilton and Elizabeth Schuyler married on December 14, 1780. So why did Hamilton try and hide such romantic words during or after their courtship? He probably didn’t. Historians believe that his son, John Church Hamilton, crossed them out before publishing the letter as a part of a book of his father’s correspondence. He may have considered the passage a little too sexy for mass consumption.

[h/t Library of Congress]

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