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Why Do Shells Sound Like the Ocean?

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Kevin in Bentonville, Arkansas, wrote in to ask this question: "Why do you hear the ocean when you put a seashell up to your ear?"

All right, first things first: no matter how much it may sound like the rolling waves, it's not actually the ocean you're hearing in a shell.

Now that we've got that out of the way, what exactly is it that you're hearing? In a word, noise; the ambient noise that's being produced all around and inside you, which you normally don't hear or pay attention to because it's too quiet.

To amplify this noise so you can hear it clearly, you need a resonator. Want to make one on the cheap? Form an O shape with your mouth and flick your finger against your throat or cheek. You should hear a note. Make a smaller or larger O, or change the shape of your mouth, and you'll get different notes. Sort of like this. What you're doing here is letting your mouth fulfill its potential as a Helmholtz resonator, where sound is produced by air vibrating in a cavity with one opening. Different pitches can be coaxed out by changing the shape of the resonating cavity.

The seashell you're listening to—the inside of which has many hard, curved surfaces great for reflecting sound—is essentially doing the same thing you just did with your mouth. The ambient noise mentioned before—the air moving past and within the shell, the blood flowing through your head, the conversation going on in the next room—is resonating inside the cavity of the shell, being amplified and becoming clear enough for us to notice. Just like the various shapes we make with our mouths will produce different pitches, different sizes and shapes of shell sound different because different resonant chambers will amplify different frequencies.

The fact that all shells sound just a little bit like the ocean is purely coincidental. Holding any sort of Helmholtz resonator to your ear will produce a similar effect, whether that object is associated with the ocean or not. Put an empty glass over your ear or even cup your hand over it, and the sound you hear will be just about the same.

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Fact Check
A Physicist Weighs In On Whether Scrooge McDuck Could Actually Swim in a Pool of Gold Coins
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Batman has the Batcave, Superman has his Fortress of Solitude, and Scrooge McDuck has his money bin. For 70 years, the maternal uncle of Disney’s Donald Duck has been portrayed as a thrifty—some might say miserly—presence in cartoons and comics, a waterfowl who has such deep affection for his fortune that he enjoys diving into his piles of gold and luxuriating in them.

It’s a rather gross display of money worship, but is it practical? Can anyone, including an anthropomorphic Pekin duck, actually swim in their own money, or would diving headfirst into a pile of metal result only in catastrophic injury?

According to James Kakalios, Ph.D., a professor of physics at the University of Minnesota and author of the recently-released The Physics of Everyday Things as well as 2005’s The Physics of Superheroes, the question really isn’t whether someone could swim in a mass of gold. They could not. It’s more a matter of how badly they’ll be injured in the attempt.

Diving into a gold pile the Scrooge way—hands first, prayer-style, followed by your head—is the most efficient way to begin breaking bones. “Keeping his arms stiff and his elbows rigid, he’s definitely going to break his wrists,” Kakalios tells Mental Floss. “Gold is a granular material like sand, a macroscopic object. You can’t swim through sand or dive into it easily.” Launch yourself off a diving board from 3 or 4 feet up and you will meet a solid surface. Landing with your feet, a far better bet, is unlikely to result in injury—provided you try to bend your knees.

In that sense, diving into gold is not dissimilar from “diving” into a concrete floor. But with gold being granular, it might be possible to break the surface and “swim” if the friction were low enough. “A ball pit is a good example,” Kakalios says. “The balls are lightly packed and have low friction relative to one another. The key is to have objects in front of you move out of the way in order to advance.”

Despite being a fictional character, McDuck hasn’t totally ignored the impossible physics of his feat. His creator, Carl Barks, has written in repeated references over the years to the implausibility of using his money vault as a swimming pool and has depicted the villainous Beagle Boys trio as getting hurt when they tried to emulate the stunt. Scrooge smirked and said there was a “trick” to making the gold dive.

That’s led to one fan theory that McDuck has used his fortune to coat the gold coins in some kind of lubricant that would aid in reducing friction, allowing him to maneuver inside the vault. Ludicrous, yes. But is it possible? “You would need a massive amount of lube to slide your body past the coins with minimal effort,” Kakalios says. “The ball pit is easier because the weight of the elements is low. Gold is a very dense material.” Diving and swimming into it, even with lubricant, might be analogous to trying to shove your hand into a deep bowl of M&Ms, he says. “M&Ms have a low friction coating. Continuing to move is really the problem.”

Presuming McDuck could somehow maneuver himself deeper into the pile, his delicate duck bones would almost surely succumb to the crushing weight of the gold above him. By one estimate, diving under one of his 5-foot-tall gold piles would put 2492 pounds of pressure on his bill.

We'll see if he tips his top hat to any further gold-diving tricks—or if he's in a full-body cast—when Disney XD relaunches DuckTales this summer.

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