Near Miss

[John_Ford]

Watched Myth Buster the other night and they were blowing up stuff. yeah, I know nothing new. However, they did this off a movie with an underwater explosion rif. Long and the short, They used about two grams worth and didn't scratch the paint, two sticks of dynamite gave a little bit better toss. The let's over do it part used 440 pound of explosive for a pretty good cracking rooster tail and overall big boom. They had sensors out the didn't trip for the first or second one but it tripped the 50 and 100 foot sensors but not the 150' for the third. Now 440 pounds of what ever is pretty stout. How close and how much did you have to use to create target effect on a ship?

[Doug Kibbey]

Watched Myth Buster the other night and they were blowing up stuff. yeah, I know nothing new. However, they did this off a movie with an underwater explosion rif. Long and the short, They used about two grams worth and didn't scratch the paint, two sticks of dynamite gave a little bit better toss. The let's over do it part used 440 pound of explosive for a pretty good cracking rooster tail and overall big boom. They had sensors out the didn't trip for the first or second one but it tripped the 50 and 100 foot sensors but not the 150' for the third. Now 440 pounds of what ever is pretty stout. How close and how much did you have to use to create target effect on a ship?

 

Sensors are a wee spot in the water, only 1/5 greater density than water itself (assuming no air in them). The big damage occurs when you have a blast wave transmitted through water and encountering a mass of less density...like the displaced water area of a ship below the water line, or...humans (with two big ol' air cavities in them). When waves pile up against a mass of less density than water, it's bad.

[Guest aevans]

Couldn't find the clip on youtube. What type of sensors were they using? Pressure transducers to measure the blast wave or strain gauges to measure the stresses in the hull?

 

They generally use one of two types of sensors with explosives -- a range of shock stickers, which give an idea of range of g loading, and pressure sensitive disks, usually chosen to burst at some calculated lethal overpressure.

 

Hence the problem with mythbusters, they don't really do science and they definitely don't understand the concept of scaling.

 

That's not exactly accurate. They don't do very precise science and they generally don't gather large data sets. And I don't think that what they do require much attention to scale, because they usually go full scale at some point (and often serendipitously discover variances caused by scaling, if they started out with a small scale test). Also, most of what they do is in the nature of illustrating known principles, not trying to discover fundamental knowledge about the world.

[Colin]

Not to mention having a whole lot of fun doing it. Plus now they have a pretty girl to make things even better.

[Marek Tucan]

Tube artillery still works despite being "obsolete" compared to various fancy PGM's. If it sounds stupid, but works, it ain't stupid, you know?

And given the aim of the experiments, which includes getting something into TV, less sensitive methods that are camera-friendly are much more useful than übertech that gives same same PC pictures.

[Guest aevans]

What on earth are shock stickers and pressure sensitive disks? That sounds like ancient technology, probably from before you were born

 

Shock stickers are stickers that have a witness feature that activates if they are subjected to some nominal acceleration. In industry they are used to detect if shipping containers and their contents have been subjected to unacceptable jolts. ISTR the MythBusters use 25, 50, and 100 g ones most often. The purpose is to detect if an unacceptable shock has been experienced by a human analog placed near an explosive event.

 

 

Pressure sensitive disks are also known as rupture disks or burst disks -- metal disks that rupture if they are subjected to too high a pressure differential. They're used industrially in pressure relief safeties. The way the MythBusters use them is to mount them in pipes pressurized to normal atmospheric pressure. The disk sensitivity is selected so that they rupture if they are subjected to a calculated lethal overpressure. They use several at once to detect lethal overpressures at set distances from an explosion.

 

Everyone has transitioned to piezoelectric and piezoresistive electronic sensors for serious experimental work. Acceleration and similar is basically all MEMS technology now.

 

All this stuff is relatively cheap and so is the high speed DAQ and you get so much more information than anything crudely analog. They were using piezoelectrics and piezoresistives when some of the oldest guys on here were college age. Hell, I think they had some of that stuff for warhead development during WW2 (trinity, etc).

 

The MythBusters aren't trying to measure data. They're trying to demonstrate physical principles. Now I would agree that that's not research (except for the odd cases that nobody's really looked at some phenomenon). But I would say that it's a demonstration of scientifically verifiable fact, in the same way that it is done in high school physics labs -- just with a lot more energy than Mr. Wizard ever used.

[Guest JamesG123]

Plus they also intentionally make it look jury rigged and "guys in their garage" style testing, as befiting a show about urban myths. I suppose they could do rigorous carefully controlled and engineered tests, but they wouldn't be nearly as entertaining and probably couldn't get them done quickly enough for a TV series.

[Guest aevans]

Jason,

 

You're just being a crumudgeon. When they were testing purported antigravity devices, they used a lab grade gravitational anomaly detector. At other times they used other sensitive intruments. When they're trying to demonstrate gross effects, they use gross sensors. They're not trying to earn PhDs, just illustrate principles. It's still science, in the sense of finding out reliable information about the world.

[Xavier]

Yeah, I'll admit the show annoys me all to hell. The saving grace is that Kari is easy on the eyes, too bad the two twits she co-hosts with ruin the effect. They should just dispose of any pretence and have her prance around in a bikini permanently.

Now that's a great idea, a bikini-clad redhead blowing things up

[mnm]

Then anything would be called science and nobody would object

[Guest JamesG123]

Pretty bad for Tony to be calling someone else a crumudgeon. lol!

 

Yeah, I'll admit the show annoys me all to hell.

 

No one is making you watch it...