Episode 144: Duct Tape Hour 2

Air Date: May 12, 2010

Duct tape can be used to build a usable bridge across a chasm.

confirmed

Adam and Jamie began by applying force to the middle of a strip of duct tape in order to determine its breaking strength. Finding a result of 67.3 lb, they built up strands from layers of tape and Adam experimented with weaving them together to strengthen the design. They settled on a rope bridge with a 10-layer walkway, two handrails, and two stabilizing rails.

They took the bridge to Mare Island Naval Shipyard, where they could set it up across a 104-foot gap with a 50-foot drop. During test runs to pre-stretch the parts and reduce the tape’s elasticity, they decided to connect the walkway and handrails with struts in hopes of reducing the wobble. A total of 196 rolls of tape were used to build the finished bridge, which was connected to steel frames on opposite ends of the gap. Adam and Jamie both made the crossing successfully, though Jamie had a much harder time keeping his balance due to his fear of heights and/or the stress of Adam’s previous crossing. Jamie commented that the elastic nature of the tape made it a poor choice for building bridges.

Duct tape can be used to hold a completely dismantled car together so that it can be safely driven at high speed.

confirmed

Kari tore apart a car’s body and frame with the help of a squad of San Francisco firefighters. Grant and Tory then reassembled it with tape, and the Build Team took it to Naval Air Station Alameda, where they set up an obstacle course on the runway to put as much stress on the car as possible. With Kari driving 40-60 miles per hour, the car held together through 10 laps. Next they did some off-road driving in the rain; the engine stalled after several minutes, but the tape did not fail.

Duct tape can be used to hold a car in place.

confirmed

The Build Team hooked a force meter between a car’s rear bumper and a telephone pole, and found that the car could pull with a force of 1300 pounds. Based on the breaking strength data from the bridge testing, they wrapped five rolls of tape around the car and pole to bind the two together. When Grant stepped on the gas, the car stayed in place even as the tires began to smoke, with only one strip of tape breaking.

Duct tape can be used to stop a car which is traveling at 60 miles per hour (95 km/hr).

busted

The Build Team placed two concrete barricades on the Alameda runway and used one roll of tape to make a single thick strand strung between them. Driving at 40 miles per hour, Tory was able to break through easily. For further tests, the team used 100 rolls of tape to make a 3-inch-thick wall, which they hung between the barricades, and towed the car into it while Grant steered remotely. On the first test, a problem with the tow cable caused the car to hit one of the barricades; the tape took a glancing blow, but did not break. The second test ended with one of the wall’s anchor points breaking loose, while the wall itself remained intact. In the third and final test, the car hit the wall dead center and broke through, but not before the tape had stretched nearly 6 feet. Based on the amount of time and material that would be needed to construct a workable car stopper, the team declared the myth busted.

12 Comments

  1. Physics Teacher says:

    Me and my students spotted a bit of an error. The tested 67.3lb maximum force was applied at an initially perpindicular orientation to the strand of tape. At the time that the strand broke, it was forming about a 30 degree angle. The tension in each side of the strand would differ from the 67.3lb value based on the exact angle of the breakage. Coincidentally, if the angle was exactly 30 degree, then the tensional force would actually be the same, since it would create 3 vectors of equal magnitude each seperated by 120 degrees. I don’t know if this was just luck on their part, or something that they decided to leave out due to mathematical complexity.

  2. SuperSparky says:

    While I agree with the only busted myth here, I must say there was something blatantly obvious about the failure. The barrier failed because the sheet metal from the car had cut it. Anyone knows that the test was for holding back a 60mph car on the material, momentum and mass alone, but not a cutting force, which would weaken any material not just duct tape. I would like to have seen the results had the car been fitted with a curved smooth bumper without a cutting edge.

  3. grandpa says:

    I think they need a math person to determine force vectors in some of their myth tests. They should test different brands of duct tape as some are stronger than others and some have better adhesives.

    • Mythmad says:

      They have Grant Imahara. They usualy get him to do the math

    • rzitex says:

      from the looks of what I saw, (based off sheen, thickness of roll, and inside of the roll) they were using 60yrdx1.82in rolls of Duck Brand Duct Tape. I have found that before you start getting into the grade of gorilla tape (which is by definition, duct tape), that is as good as it gets.

  4. Logak says:

    I think the duct tape bridge could be potentially more stable if all the parts of it were thicker – that would reduce wobble and distention. Of course, that requires more time and energy, and the Mythbusters are on a schedule, so I don’t blame them for the lesser construction. Plus, it would probably take an even more prohibitive amount of duct tape to make such a bridge (though I imagine if you’re planning on doing this yourself, you probably already have too much free time).

  5. dewdude says:

    Look…you can break plate glass with your body quite easily. A friend of mine put his hand up to stop a classroom door wayyyy back in junior high and his hand went through the window with actually very very little effort. Plate glass will break if you move it wrong..it’s fragile stuff.

  6. Jayvee says:

    actually like a tissue paper that if you will not twist it around it would be weaker but if you will twist it it will stronger will it be.

  7. jf says:

    I agree about the duct tape rail…it was cut, thus it failed. It would be real interesting if they could find a way to prevent cutting of the duct tape on that experience categorized as busted…

  8. kirk says:

    if they rolled the tape up length wise to make duct tape……rope and then braided & the braides braided again ect…..

    they only used flat tape look at how rope and cable are made

    even look and the jail break Episode the T.P. and pony tail rope!!!!!!!!!!!!!!!

  9. Chris says:

    Just watched this episode…kinda a year late. Anyhoo, walking on a bridge of this design requires technique. The key: don’t look down, just look at the end. Duct tape or 70′s Cdn Army rope is the same. ;-) Adam seemed to get it…Jamie not so much,but I am sure he’d do better on a do-over with my advice. :-)

  10. Mike says:

    Can you fix a piano with duct tape?

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