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Why Do Some Sounds Make People Sick?

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While playing music too loudly can damage hearing, there are other things you should know about the effects of some sounds on the human body.

Decibels are used to measure the intensity of sounds (prolonged exposure to sounds above 85 dB can cause hearing loss), and frequency, which is measured in Hertz (Hz), refers to the amount of times a sound wave occurs each second. Human ears can generally pick up on sounds that fall in the 20Hz to 20KHz range. Frequencies above that are called ultrasonic, and frequencies below 20Hz are sometimes referred to as infrasonic. Infrasonic sound is both naturally occurring (earthquakes, ocean waves, upper-atmospheric lightning, etc.) and man-made. Some studies have shown that at high intensities, infrasonic sounds can have extra-aural bioeffects, including nausea, headaches, and dizziness, but why? The short answer: bad vibrations.

Sound is a wave of pressure traveling through a medium. Infrasonic sound, for example, has a long wavelength that, according to Popular Science, “makes it much more capable of bending around or penetrating your body, creating an oscillating pressure system.” Every object, including parts of the body, has a natural frequency at which it vibrates, a phenomenon known as resonance. Popular Science has more to say about how low-frequency resonance affects the body:

“Human eyeballs are fluid-filled ovoids, lungs are gas-filled membranes, and the human abdomen contains a variety of liquid-, solid-, and gas-filled pockets. All of these structures have limits to how much they can stretch when subjected to force, so if you provide enough power behind a vibration, they will stretch and shrink in time with the low-frequency vibrations of the air molecules around them.”

A 1983 study on human body vibration exposure published in The Journal of the Acoustical Society of America found that

“exposure to vertical vibrations in the 5-10 Hz range generally causes resonance in the thoracic-abdominal system, at 20-30 Hz in the head-neck-shoulder system, and at 60-90 Hz in the eyeball. When vibrations are attenuated in the body, its energy is absorbed by the tissue and organs...Vibration leads to both voluntary and involuntary contractions of muscles, and can cause local muscle fatigue, particularly when the vibration is at the resonant-frequency level. Furthermore, it may cause reflex contractions, which will reduce motor performance capabilities.”

Other studies suggest that low-frequency noises, like those produced by wind turbines, trigger a reaction in the brain that could lead to adverse health effects. The frequencies have also been linked to changes in respiratory rhythms due to chest-wall vibration, with varying results depending on whether the subject is standing or sitting (resonance occurs at different levels depending on body position). Infrasound has been used at haunted houses to make visitors feel uneasy, and some believe that there is a “brown note” (around 9Hz) that could cause bowels to release (though this was “busted” by Adam Savage and Jamie Hyneman on Mythbusters).

More research is needed to fully understand why some people are affected and others are not, but engineers have been developing sound-dampening technology for turbines, and some doctors have suggested that noise-canceling headphones may help in other cases.

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Why You Should Never Take Your Shoes Off On an Airplane
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What should be worn during takeoff?

Tony Luna:

If you are a frequent flyer, you may often notice that some passengers like to kick off their shoes the moment they've settled down into their seats.

As an ex-flight attendant, I'm here to tell you that it is a dangerous thing to do. Why?

Besides stinking up the whole cabin, footwear is essential during an airplane emergency, even though it is not part of the flight safety information.

During an emergency, all sorts of debris and unpleasant ground surfaces will block your way toward the exit, as well as outside the aircraft. If your feet aren't properly covered, you'll have a hard time making your way to safety.

Imagine destroying your bare feet as you run down the aisle covered with broken glass, fires, and metal shards. Kind of like John McClane in Die Hard, but worse. Ouch!

Bruce Willis stars in 'Die Hard' (1988)
20th Century Fox Home Entertainment

A mere couple of seconds delay during an emergency evacuation can be a matter of life and death, especially in an enclosed environment. Not to mention the entire aircraft will likely be engulfed in panic and chaos.

So, the next time you go on a plane trip, please keep your shoes on during takeoff, even if it is uncomfortable.

You can slip on a pair of bathroom slippers if you really need to let your toes breathe. They're pretty useless in a real emergency evacuation, but at least they're better than going barefoot.

This post originally appeared on Quora. Click here to view.

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Big Questions
Where Should You Place the Apostrophe in President's Day?
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Happy Presidents’ Day! Or is it President’s Day? Or Presidents Day? What you call the national holiday depends on where you are, who you’re honoring, and how you think we’re celebrating.

Saying "President’s Day" infers that the day belongs to a singular president, such as George Washington or Abraham Lincoln, whose birthdays are the basis for the holiday. On the other hand, referring to it as "Presidents’ Day" means that the day belongs to all of the presidents—that it’s their day collectively. Finally, calling the day "Presidents Day"—plural with no apostrophe—would indicate that we’re honoring all POTUSes past and present (yes, even Andrew Johnson), but that no one president actually owns the day.

You would think that in the nearly 140 years since "Washington’s Birthday" was declared a holiday in 1879, someone would have officially declared a way to spell the day. But in fact, even the White House itself hasn’t chosen a single variation for its style guide. They spelled it “President’s Day” here and “Presidents’ Day” here.


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Maybe that indecision comes from the fact that Presidents Day isn’t even a federal holiday. The federal holiday is technically still called “Washington’s Birthday,” and states can choose to call it whatever they want. Some states, like Iowa, don’t officially acknowledge the day at all. And the location of the punctuation mark is a moot point when individual states choose to call it something else entirely, like “George Washington’s Birthday and Daisy Gatson Bates Day” in Arkansas, or “Birthdays of George Washington/Thomas Jefferson” in Alabama. (Alabama loves to split birthday celebrations, by the way; the third Monday in January celebrates both Martin Luther King, Jr., and Robert E. Lee.)

You can look to official grammar sources to declare the right way, but even they don’t agree. The AP Stylebook prefers “Presidents Day,” while Chicago Style uses “Presidents’ Day.”

The bottom line: There’s no rhyme or reason to any of it. Go with what feels right. And even then, if you’re in one of those states that has chosen to spell it “President’s Day”—Washington, for example—and you use one of the grammar book stylings instead, you’re still technically wrong.

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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