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Episode 31: Breaking Glass, A Rolling Stone Gathers No Moss, Shop-Vac Jet Engine

  • Breaking Glass: an unassisted human voice can shatter a glass confirmed
  • "A Rolling Stone Gathers No Moss": confirmed
  • Shop-Vac jet engine: a shop-vac + gas = jet engine mythbusted

The star myth of this show was the Breaking Glass myth. They got rock singer Jamie Vendera to break the glass on camera, unassisted, which they claim is the first documented video evidence of this ever happening. A surprising claim, but very cool slo-mo video.

Breaking Glass

Myth: You can breaking a crystal glass by singing

They got Roger Schwenke from Meyer Sound to help out again with the sound setup (worked on the Brown Note and Duck Quack myths as well). They also got Jamie Vendera, rock singer and vocal coach, to attempt the myth.


Their researchers could find no video evidence of a voice shattering a glass. Caruso, the opera singer, claimed he had done it, but his wife disputed that claim after his death. There was a Memorex commercial with Ella Fitzgerald shattering a glass, but that used speaker amplification. Jamie Vendera, who would be attempting to break the glass on the showed, claimed that his vocal teacher Jim Gillette from Nitro used to break glasses with amplification before every concert.

Adam's claim: if Vendera is successful, it will be the first time that this has ever been documented on film. "If our researchers can't find it, nobody can"

Electronic tone + speakers + glass

  • fundamental frequency: Schwenke's idea is to play the fundamental frequency of the glass back at it in order to get it to break. The fundamental frequency is the main frequency you get when you flick a crystal glass to make it ring. In this case, the fundamental frequency of their glass was 562 hertz. no breaking glass
  • fundamental frequency + harmonics: they amended their plan to include the harmonic frequencies. no breaking glass, though it did vibrate quite a bit.
  • board with a 2" hole: Schwenke added a board with a 2" hole through it to the front of the speaker to change the direction of the sound waves. The glass broke immediately

Human voice with amplification

They got Jamie Vendera, rock singer, to attempt breaking a glass using amplification through a speaker with the board with a hole. Vendera broke the glass easily.

Vendera then gave Jamie and Adam some quick lessons ("You've got to slide slowly up or slowly down") and they could give it a try. Jamie couldn't hit the right pitch. Adam's first attempt failed. "Tighten the sphincter." His second attempt broke it almost immediately.

Human voice with no amplification

This was the big test: no amplification with Vendera singing with his lips almost directly against the glass.

After 12 glasses: no breakage

Adam gave it a try: "The best case scenario shatters in my face, how do you think that makes me feel?" Not surprisingly, Adam couldn't do it.

Vendera came back (20th attempt): BREAK!

confirmed: an unassisted human voice can break a glass

A Rolling Stone Gathers No Moss

Myth: "A rolling stone gathers no moss"

This is the longest myth ever tested on MythBusters.

'Gathering' = 'Collecting'

Tory philosophized the meaning of 'gathers': does it mean grow on or merely to catch moss as it rolls. To test the 'collect' meaning they went to a hill, rolled some stones, and verified that a rolling stone can in fact catch moss while rolling.

'Gathering' = 'Growing'

They built an irrigated barrel, split in two. One half spun continuously while the control half remained still. Three rocks were placed in each half. Some matting was added to the rig to keep it moist.

They enlisted the help of Brent Mishler, Moss Professor, to find good moss. Mishler recommended equal parts buttermilk and moss, grinded in a coffee grinder, to spread over the rocks and the run.

Tory used a hammer drill to grind up the buttermilk and moss mixture into a chunky paste, ignoring the recommendation of Mishler that it needed to be a smooth mixture. The chunky paste was applied to the rocks and the track. Tory's mistake ended up costing them six weeks of useless testing: none of the rocks, even the ones that were still, grew moss, though a rock that already had moss grew more moss.

Jamie: "I thought this was going to be an easy, simple experiment, but you screwed it up."

After making the mixture properly this time, they once again started got things rolling. This time they let it go for six months, making this the longest experiment in MythBusters history.


  • All of their stationary rocks grew moss.
  • None of the rolling rocks grew moss.

They interpreted the spirit of the myth to mean that a rolling stone grows no moss, which their rolling barrel test demonstrated.

confirmed: a rolling stone gathers no moss

Shop-Vac Jet Engine

Myth: A guy was cleaning his pool and heard an explosion. He went to his neighbor's house -- his neighbor was using a shop-vac to get the sediment off the bottom of the gas tank in his boat. The fumes went through the shop-vac and turned it into a turbine engine.

Test 1: Shop-Vac + Gas Can

They put a small amount of gas in a gas can so that it was mostly full of fumes. They hooked it up to a shop-vac for five minutes to see if they could get an explosion.

No explosion. It turns out that the shop-vac that they had chosen, like most new shop-vacs, has a safety feature: the motor is isolated from the tank and air running through the tank, so the motor can't spark the fumes.

Test 2: Short-circuited shop-vac + Gas Can

By accident, they short-circuited their shop-vac parts, sending sparks everywhere. Happy with this discovery, they decide to rig a worst-case shop-vac: short-circuit and a hole drilled through to allow the spark to reach the fumes. They also added more gas to the gas can.

No explosion.

Test 3: Creating a Jet-engine out of Vacuum Parts

Tory went to A&G Vacuum shop to pick up some more vacuums. A&G Vacuum was the site of Adam's facial run-in with a vacuum motor (Adam decided to stick his face near a motor, which pulled in and chopped up his lip). The Vacuum Man showed Tory an older vacuum that was capable of sparking fumes into a fire.

This proved that it's possible for a vacuum to catch on fire, but it didn't turn into a jet engine. With this in mind, Tory was tasked with replicating the results of the myth, i.e. creating a jet-engine out of vacuum parts.

Tory's design:

  • Vacuum motor sucks in air into a tube
  • Fuel injector made from a propane ring from a propane stove
  • Flame catcher made from a conical strainer
  • Fans at back

Tory: "There are going to be a lot of engineers out there going, 'What the hell is he doing?' and I'm asking myself that on a moment-by-moment basis, 'What the hell am I doing?'"

Tory's vacuum-based jet-engine was hung up chamber with an ignitor. First try: no ignition. Tory moved the ignitor to the end of the engine. Second try: still no ignition. Tory then tried an open flame at the end of the chamber: finally, ignition.

There was a tiny, tiny bit of thrust when the vacuum motor started, but for the most part it just tossed flames around the chamber.

Jamie's explanation:

"The whole concept of a vacuum cleaner being a jet engine is all wrong. It goes against the principles that make jet engines. Vacuum cleaner create vacuums, that's low pressure. A jet engine works by creating more pressure, which completes the compression, so it's just not practical."



i have made a jet engine out of a turbocharger following basically the same principals. There is no vacuum created by the jet engine so that solves the problem. From expirience I know it works.

im pretty sure diamanda galas probably has video of her voice breaking glass.

Thank for your website but the pics don't seem to appear. Well i went to the airforce workshop and they assured me that it will work! Basicly what you do in this consept is building an afterburner. Now go for it!

Hmm. Vacuum cleaner? I think the myth is all wrong in the first place. You need a leaf blower to make a jet engine--and an afterburner.

I was having a talk with my co-workers. And some how we where talking about Sayings that people use but do not why. And we talked about how a Rolling stone/rock gathers no moss. I do not see that is possible. I have a hard time thinking that even on the smallest level that stone/rock gathered no moss. Please if anyone knows of a law or theory stating that you can't touch something without leaving some thing behind let me know.

I seem to remember an edition of the Paul Daniels Magic Show from back in the 1980s which had an opera singer breaking a glass with just her voice.

IIRC she used some sort of "tube" to keep her away from breaking glass and to focus her voice.

Did anyone else see this?

@Zacharia I've seen this, didn't know anyone else could remember this :) Good old times.