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5 Surprising Things That Have Broken the Speed of Sound

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by Kenny Hemphill

You might already know that in 1947, U.S. test pilot Chuck Yeager was the first person to break the sound barrier in a Bell X-1 named the Glamorous Glennis. But aircraft aren't the only things that break the sound barrier. Here are a few other items that may surprise you.

1. PEOPLE

When Felix Baumgartner jumped out of a balloon 24 miles above New Mexico in 2012, he broke more than the world record for the highest-ever freefall. About a third of the way down, Baumgartner reached Mach 1.25 or 843.6 mph, and in doing so became the first person to break the sound barrier while in freefall.

Having beaten a freefall record that had existed for 52 years, however, Baumgartner only held it for two years, when it was beaten again by Google exec Alan Eustace. He also broke the sound barrier, though he didn't hit as impressive a maximum speed as Baumgartner, reaching a measly 822 miles per hour, or Mach 1.23.

2. PING PONG BALLS

Anyone who's watched the top table tennis players in action knows they hit the ball hard and that it travels almost too quickly for the eye to see. But even that pales in comparison to the air-powered cannon built in 2013 by students at Indiana's Purdue University, which fired ping pong balls at more than 900 mph. “You can get really, really high accelerations, the ball comes out of the barrel intact and doesn’t break until it actually hits something,” mechanical engineer Mark French Inside Science. The cannon used a vacuum pump to suck the air from a sealed tube, the air rushed to a nozzle shaped like an hour glass, and the nozzle propelled the ping pong balls at supersonic speed—about 919 mph. Remarkably, given their light weight and poor aerodynamics, the ping pong balls delivered as much energy to their target as a brick falling several stories.

3. WHIPS

You know that crack a bullwhip makes when it's wielded in anger by an expert? That's a sonic boom, the shockwave created when the tip of the whip breaks the sound barrier. Or at least, that had been the presumption until researchers at the University of Arizona spoiled it for everyone.

They were puzzled as to why, if the crack is a sonic boom, it doesn't occur until the whip's tip is traveling at almost twice the speed of sound. It turns out that the cracking noise is actually created by a loop traveling along the whip, picking up speed. And when it reaches the speed of sound, it creates a sonic boom.

4. A TOWEL

Snapping a towel in the changing room is dangerous—you could, in all seriousness, take someone's eye out. The reason it's so dangerous has partly to do with the speed the end of the towel is traveling. Like a bullwhip, it goes very fast indeed.

In 1993, a group of students at North Carolina School of Science and Mathematics set out to prove that a properly whipped towel could break the sound barrier. They rigged up a high-speed photography kit that would allow them to measure the distance the tip of the towel was traveling at the moment they thought the barrier would be broken. After the experiment, it seemed like they had managed to break the barrier—but the students felt their results were inconclusive.

So they tweaked the experimental setup (and, according to some sources, swapped the towel for a cut down bedsheet) which eventually allowed them to break the sound barrier. But there was another caveat: The team cautioned that they still got snaps when it didn’t appear that they had broken the barrier. The theory was that their camera wasn’t fast enough to catch subsequent supersonic moments, but it remains a mystery.

5. AIR

Here's an odd one to finish with. According to one study, when a rock or other such object is dropped into water, an hourglass-shaped cavity of air is created, which then ejects the air at speeds faster than the speed of sound.

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Space
The Fascinating Device Astronauts Use to Weigh Themselves in Space

Most every scale on Earth, from the kind bakers use to measure ingredients to those doctors use to weigh patients, depends on gravity to function. Weight, after all, is just the mass of an object times the acceleration of gravity that’s pushing it toward Earth. That means astronauts have to use unconventional tools when recording changes to their bodies in space, as SciShow explains in the video below.

While weight as we know it technically doesn’t exist in zero-gravity conditions, mass does. Living in space can have drastic effects on a person’s body, and measuring mass is one way to keep track of these changes.

In place of a scale, NASA astronauts use something called a Space Linear Acceleration Mass Measurement Device (SLAMMD) to “weigh” themselves. Once they mount the pogo stick-like contraption it moves them a meter using a built-in spring. Heavier passengers take longer to drag, while a SLAMMD with no passenger at all takes the least time to move. Using the amount of time it takes to cover a meter, the machine can calculate the mass of the person riding it.

Measuring weight isn’t the only everyday activity that’s complicated in space. Astronauts have been forced to develop clever ways to brush their teeth, clip their nails, and even sleep without gravity.

[h/t SciShow]

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Essential Science
What Is Infinity?
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Albert Einstein famously said: “Two things are infinite: the universe and human stupidity. And I'm not sure about the universe.”

The notion of infinity has been pondered by the greatest minds over the ages, from Aristotle to German mathematician Georg Cantor. To most people today, it is something that is never-ending or has no limit. But if you really start to think about what that means, it might blow your mind. Is infinity just an abstract concept? Or can it exist in the real world?

THERE'S MORE THAN ONE KIND

Infinity is firmly rooted in mathematics. But according to Justin Moore, a math researcher at Cornell University in Ithaca, New York, even within the field there are slightly different uses of the word. “It's often referred to as a sort of virtual number at the end of the real number line,” he tells Mental Floss. “Or it can mean something too big to be counted by a whole number.”

There isn't just one type of infinity, either. Counting, for example, represents a type of infinity that is unbounded—what's known as a potential infinity. In theory, you can go on counting forever without ever reaching a largest number. However, infinity can be bounded, too, like the infinity symbol, for example. You can loop around it an unlimited number of times, but you must follow its contour—or boundary.

All infinities may not be equal, either. At the end of the 19th century, Cantor controversially proved that some collections of counting numbers are bigger than the counting numbers themselves. Since the counting numbers are already infinite, it means that some infinities are larger than others. He also showed that some types of infinities may be uncountable, as opposed to collections like the counting numbers.

"At the time, it was shocking—a real surprise," Oystein Linnebo, who researches philosophies of logic and mathematics at the University of Oslo, tells Mental Floss. "But over the course of a few decades, it got absorbed into mathematics."

Without infinity, many mathematical concepts would fall apart. The famous mathematical constant pi, for example, which is essential to many formulas involving the geometry of circles, spheres, and ellipses, is intrinsically linked to infinity. As an irrational number—a number that can't simply be expressed by a fraction—it's made up of an endless string of decimals.

And if infinity didn't exist, it would mean that there is a biggest number. "That would be a complete no-no," says Linnebo. Any number can be used to find an even bigger number, so it just wouldn't work, he says.

CAN YOU MEASURE THE IMMEASURABLE?

In the real world, though, infinity has yet to be pinned down. Perhaps you've seen infinite reflections in a pair of parallel mirrors on opposite sides of a room. But that's an optical effect—the objects themselves are not infinite, of course. "It's highly controversial and dubious whether you have infinities in the real world," says Linnebo. "Infinity has never been measured."

Trying to measure infinity to prove it exists might in itself be a futile task. Measurement implies a finite quantity, so the result would be the absence of a concrete amount. "The reading would be off the scale, and that's all you would be able to tell," says Linnebo.

The hunt for infinity in the real world has often turned to the universe—the biggest real thing that we know of. Yet there is no proof as to whether it is infinite or just very large. Einstein proposed that the universe is finite but unbounded—some sort of cross between the two. He described it as a variation of a sphere that is impossible to imagine.

We tend to think of infinity as being large, but some mathematicians have tried to seek out the infinitely small. In theory, if you take a segment between two points on a line, you should be able to divide it in two over and over again indefinitely. (This is the Xeno paradox known as dichotomy.) But if you try to apply the same logic to matter, you hit a roadblock. You can break down real-world objects into smaller and smaller pieces until you reach atoms and their elementary particles, such as electrons and the components of protons and neutrons. According to current knowledge, subatomic particles can't be broken down any further.

THE INFINITIES OF THE SINGULARITY

Black holes may be the closest we've come to detecting infinity in the real world. In the center of a black hole, a point called a singularity is a one-dimensional dot that is thought to contain a huge mass. Physicists theorize that at this bizarre location, some of the singularity's properties are infinite, such as density and curvature.

At the singularity, most of the laws of physics no longer work because these infinite quantities "break" many equations. Space and time, for example, are no longer two separate entities, and seem to merge.

According to Linnebo, though, black holes are far from being an example of a tangible infinity. "My impression is that the majority of physicists would say that is where our theory breaks down," he says. "When you get infinite curvature or density, you are beyond the area where the theory applies."

New theories may therefore be needed to describe this location, which seems to transcend what is possible in the physical world.

For now, infinity remains in the realm of the abstract. The human mind seems to have created the concept, yet can we even really picture what it looks like? Perhaps to truly envision it, our minds would need to be infinite as well.

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