5 SURPRISING THINGS THAT HAVE BROKEN THE SPEED OF SOUND

5 Surprising Things That Have Broken the Speed of Sound
By Kenny Hemphill, Mental Floss, 9 February 2017.

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

Image credit: matthewwu88/Flickr, CC BY 2.0.

When Felix Baumgartner jumped out of a balloon 24 miles above New Mexico in 2012 [pictured above], 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

A bullwhip. Image credit: Pilgrim70/Wikimedia Commons.

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

Towel destroying a Monster can. Image credit: Devin Schmitt via trailsforever.blogspot.com.

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

Image credit: PublicDomainPictures/Pixabay

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.

Top image: Speed of sound. Credit: Dg-505/Wikimedia Commons.

[Source: Mental Floss. Edited. Some images and links added.]