Episode 60: Earthquake Machine, Exploding Lava Lamp
- Earthquake Machine: Nicola Tesla invented a device capable of generating earthquakes. busted
- Exploding Lava Lamp (and other household items on stove): a lava lamp on a stove can explode with lethal force. confirmed. Other household items tested include:
- can of beans: small cans probably not lethal but larger cans could be
- canned meat (spam): probably non-lethal
- glass jar of milk: possibly lethal if you were looking directly down on it.
- "Big Bertha" lava lamp: the lamp broke into small spears of glass and shot around. confirmed lethal
Watching slo-mo video of lava lamps exploding was more fun than watching actual lava lamps, but I'm not sure where the MythBusters even found a glass jar of milk. I found the small explosions to be more interesting than the Tesla earthquake myth, given that there was no real way in which the MythBusters were going to replicate the myth this time around. They were surprised at their ability to get the old Carquinez bridge to vibrate, but nothing was violently shaken apart.
Tesla's Earthquake Machine
Myth: Nicola Tesla invented a working earthquake machine
Tesla claimed multiple devices of mass destruction, including a death ray that could destroy 10,000 airplanes and the ability to split the Earth in two with some well-timed explosions. The MythBusters focused on Tesla's own recounting of an earthquake machine that he built.
"I was experimenting with vibrations. I had one of my machines going and I wanted to see if I could get it tune with the vibration of the building. I put it up notch after notch. Suddenly, all the heavy machinery in the place was flying around. I grabbed a hammer and broke the machine. Outside in the street there was pandemonium. The police and ambulance arrived. We told the police it must have been an earthquake. I told my assistants to say nothing."
Tesla also described testing his machine on a 2 foot steel bar:
"For a long time nothing happened. But at last the great steel link became to tremble and finally broke. Crowbars could not have done it, but a fusilade of taps, none of which would have harmed baby, did it."
Searching the patent office, they were able to come up with Tesla's design for the earthquake machine: the Tesla Oscillator. The design was a mechanical oscillator generator featuring a central rod, motor, and air cushion. The speed of the vibration of the rod could be manipulated and Tesla claimed with proper tuning, it could destroy anything.
The destructive powers of mechanical resonance are well-known, with perhaps one of the most famous events being the Tacoma Narrows Bridge collapse. In their very first season, the MythBusters tested this idea with marching soldiers aka "Breakstep Bridge", which was shown to be plausible under revisiting (revisiting was cut from actual episode).
They built their first prototype using a jackhammer, which has the mechanical oscillation requirement of Tesla's machine. They replaced the chisel with a rod, added an air cushion, and made the frequency tunable -- viola, Tesla Oscillator. But it didn't run very well. Jamie and Adam argued over the design, focusing in on the air spring, which was causing it to oscillate very slowly -- 2-3 hertz. Adam wanted the air spring to stay exact to Tesla's device, but Jamie wasn't happy with the ineffiencies that the air cushion was creating.
Prototype 2: Mechanical springs
Adam and Jamie came up with a compromise that was compatible with Tesla's requirements: Jamie replaced the air cushion with mechanical springs. Tesla had preferred air cushions over mechanical springs because they have no inclination to break. They tested their prototype on a 2 foot bar to replicate Tesla's initial test. The MythBusters had a bit of trouble replicating Tesla's test -- amusingly enough, the mechanical springs that Tesla noted had an inclination to break, broke.
With two failed prototypes, they decided to go back to the drawing board with some visualization tests. They setup a water tank with a bulb bouncing up and down in it. Minute variations in the frequency of the bulb -- 1.5 to 1.6 -- caused major variations in the waves in the tank. With the principles of mechanical resonance visualized in their heads, they went back to prototyping.
Prototype 3: air-powered autotool
They next tried an air-powered autotool that was already so close to Tesla's design that all they had to do was mount a plate on it -- so that it could be attached to the target object. They tried running the test on the 2 foot steel bar again, but they couldn't tune the device and the bar: the frequency of the device was about 52 hertz; the lowest natural frequency of the bar was in the hundreds. They next tried a 2' foot bar of 2" square tubing -- they got a bit more shaking, but not enough. Then they went to a 20' bar, which had a natural frequency of 7 hertz. Still no destructive vibrations.
Prototype 4: Grant's electromagnetic linear motor
Grant already had an electromagnetic linear motor in his possession for an outside consulting gig. The motor was frictionless, like Tesla described, and it was also tunable in .01 hertz increments. All they had to do was clamp the motor to the side of the steel bar. The 20 foot bar started bouncing up and down with a steady beat -- the deflection from the 5lb device was much more than Adam standing on it could create.
1/6 scale test
They built a 1/6 scale of Tesla's building and a 1/6 scale oscillator out of a microcassette recorder. Nothing happened. Breaking with their scale, they attached Grant's device to the mock building, which didn't produce destructive forces either. At this point, the MythBusters were about ready to call it busted, but Adam wanted to attach Grant's motor to a large structure -- like a bridge -- to see what would happen.
They went out to the old span (circa 1927) of the Carquinez bridge (Wikipedia article) that links Vallejo, CA, to Crockett. The old span is a steel cantilever design and was the first major bridge in the San Francisco Bay Area.
Grant's motor was clamped to one of the bridge supports and they began the process of tuning in the motor. Adam and Jamie stood on the bridge as they were doing this, showing their confidence in this being busted. Adam: "MythBusters is nothing if not a compendium of ways in which Jamie and I have been wrong."
To their surprise, they were able to get the entire bridge to start oscillating. Adam could feel the vibrations hundreds of feet and several supports away. Jamie compared the vibrations he was feeling to a big semitrailer truck cruising by. Jamie: "It actually makes a little concerned, believe it or not."
After an hour of testing, though, they weren't able to get anything stronger than the vibrations they initially felt. No earthquake.
Exploding Lava Lamp
Myth: In 2004, a Washington state resident was killed by a lava lamp left on a stove -- it exploded and pierced his heart with a shard of glass.
Kari went to The Bone Room to check obtain a human rib cage and cast a ballistics gel mold around it. She also suspended a balloon heart inside so they could easily tell if it was pierced.
Grant investigated the contents of lava lamps and found many potentially flammable contents: mineral oils, wax, and alcohol.
- lava lamp bottle
- portable stove
- ballistics gel chest positioned close to the stove
Test 1: safety-cap-style lava lamp
The stuck the lava lamp bottle on the stove. After a bit of heating, the safety cap of the lamp blew off, hot lava lamp contents geysered out of the top, and with no liquid left in the bottle, it quickly shattered on top of the stove.
Test 2: bottle-cap-style lava lamp
They next test a bottle-cap style lava lamp. There was a small leak out of the top of the lamp at the pressure built up, which lead to flames leaping over the bottle. The bottle exploded everywhere and left some pieces of glass on the ballistics gel chest -- no wounds, but definitely potential for injury.
Test 3: securely fastened bottle top
The bottle cap in the second test allowed some of the pressure to escape, so Tory epoxied the top of the next test lamp to help the pressure build up even more. It wasn't enough epoxy, though, as the bottle still leaked out of the side. They decided to help the explosion along by squirting some cold water onto the lamp.
Grant: "The theory was that the shock of the cold water would cause the glass to fracture -- BOOM!"
As Grant was speaking while shooting the cold water, the lava lamp exploded. A large shard of glass was left in the ballistics gel chest.
They didn't want to stop there, though. For fun they decided to start testing other household objects placed on stoves.
- can of beans: Tory: "Not as exciting as the lava lamp, this can of beans." The top of can popped open and the contents came shooting out, mostly intact and can-shaped, and landed on the stovetop. Non-lethal.
- big can of beans: after much waiting, they got a good-sized explosion. Tory: "I can taste beans in the air". Possibly lethal
- canned meat (spam): very similar small can of beans: the top popped open and the contents popped out. Non-lethal
- jar of milk: the jar exploded mostly upwards, though the bottom half did slide over to the ballistics gel chest. Possibly lethal if you were looking directly down on it.
- big bertha lava lamp: the lamp broke into small spears of glass and shot around. Possibly lethal.