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Episode 38: MythBusters Revisted 2

Upheld:

  • Explosive Decompression: A gunshot cannot cause a pressurized plane to explosively decompress (original episode summary). still busted
  • Blown Away: Does getting shot throw you back through the air? still busted
  • Plywood Builder: You can glide to safety holding onto a piece of plywood. still busted

Overturned:

  • Running in the rain: It is better to run in the rain instead of walk (original episode summary). confirmed
  • Revisit of the Biscuit Bazooka Revisit (episode summary of first revisit): cola cans can explode if left inside a hot car. They confirmed this as true without testing. Instead they did a test to find that (surprise) black cars get hotter than white cars.

Neither nor:

  • A/C vs. Windows Down: You save more gas driving with the A/C on than with the windows down (original episode summary). Answer: it depends on the speed you're driving at.
  • Exploding gas tank: a car can explode when the gas tank is shot (original episode summary). They redid this with tracer rounds and confirmed that tracer rounds can ignite a gas tank. This doesn't contradict their original result that ordinary (legal) bullets cannot.

Explosive Decompression

Myth: A gunshot cannot cause a pressurized plane to explosively decompress (original explosive decompression episode summary)

Error according to the viewers: in a flying plane the result would be different because air would travel over the bullet hole and lead to catastrophic results. The air flow creates a low pressure zone over the hole that pulls air out of the plane.

New setup: they took the door from the original myth and created an airtight chamber for one side of it. Air was run over the other side and the pressure differential created by the swirling air on the outside was measured.

Test results

Using some fans they were able to generate 19.1mph winds: 0.002psi differential

Grant: "I think Adam has had more explosive farts than that"

Using the jetpack fans they generated 38mph winds: 0.02psi

Strapped into back Tory's truck driving 65mph: 0.05psi (very noisy datapoint)

They calculated that at 500mph there would be a 1.4psi differential created by airflow over the hole. In the original mythbusting they tested at 8.5psi, so even with 1.4psi tacked on it still wouldn't be enough for explosive decompression.

still busted

Blown Away Revisited

Myth: Does getting shot throw you back through the air?

Error according to the viewers: because the pig and Buster were hung from a hook, their center of gravity was wrong. They should have been supported by the chest. My personal opinion is that this is all very silly. The explanation that you would have be blown back an equal distance from the recoil should be enough.

The new rig: Buster will be supported from the chest instead and they even threw in a more powerful 50 caliber. They also gave buster a bulletproof plate so that as much of the bullet's energy would be absorbed as possible.

Results

Deer slug: Buster fell down but barely any distance backwards

50 caliber: Buster slumped down, no flying back

still busted

Running in the rain

Myth: do you get wetter running in the rain running instead of walking? (original episode summary)

Error according to the viewers: they didn't use real rain.

New setup: They waited for actual rain and walked/ran around the parking lot in overalls and a hat, with a sweat-barrier rubber suit underneath.

Results

The first attempt done by Adam and Jamie was interrupted by the rain stopping mid-test. They handed off the duties to Tory and Grant, who donned the gear on a rainy day and did a short loop outside. They found that, on average, the runner collected 4g less water than the walker.

confirmed

NOTE: according to this BBC Magazine mathematical analysis by Nick Allen, you get most wet if you run very fast or stay in the rain a very long time. This confirms the original mythbusting and contradicts the results of the revisit.

Biscuit Bazooka (Revisit of a revisit)

Myth: in the original myth they used biscuit cans, which they got to explode. In the first revisit, they also did aerosols and cola cans, but weren't able to get any explosions unless they stuck the cola in a 300 degree oven. (episode summary from first revisit)

Error according to the viewers: They didn't wait long enough as cola will explode at 140 degrees.

New setup: instead of getting the cola to explode in the car, they decided to setup a white and black car and answer another viewer's question, which color of car gets hotter in the sun?

Results: after four hours into experiment the black car was 135 degrees, the white car was 126 degrees.

Plywood Builder

Myth: A builder got blown off a roof while holding a piece of plywood. The plywood allowed him to safely glide back into the building.

Error according to the viewers: they didn't take updraft into account

In the original mythbusting, it was difficult to even hold on to the plywood at low speeds. Wind speeds at the top of skyscrapers can reach 90mph.

New setup: They strapped Tory into the back of his pickup truck, where he held onto the piece of plywood. They looked for both the best angle for lift as well as for what speed Tory could no longer hold onto the plywood. For test 2 they slightly modified to setup so that Tory could hang from the plywood instead of having to hold it over his head.

Results (Test 1)

First run: Tory started with the plywood vertical. At 45mph he couldn't hold onto the plywood and he never managed to get into position.

Second run: Tory started with the board horizontal over his head, dropping it at 15mph.

Results (Test 1)

They wanted to eliminate gravity as a factor in the test as holding the plywood over his head without wind was difficult for Tory. They added braces underneath the plywood so that Tory could hang from the plywood.

Tory got a bit of lift from the plywood, but at 40mph he could no longer hold onto the plywood.

The results were similar to the original busting: whlie you can get some lift from the plywood, you wouldn't be able to hold onto it.

*busted again

A/C vs. Windows Down

Myth: You save more gas driving with the A/C on than with the windows down (original A/C vs. windows down episode summary)

In the original mythbusting, they did a test at 55mph and A/C was more efficient. However, they used a computer to estimate gas consumption and they didn't trust it. They did another test at 45mph and drove until the tanks emptied. In this second test, open windows won by a wide margin. They judged the latter test to be the correct result.

Error according to viewers: As you go faster, open window drag increases to a point where A/C becomes more efficient.

Court of appeals decision: both results from the original test were correct. At high speeds A/C is more efficient. At low speeds open windows is more efficient. They marked it busted, but I'm not sure what that means.

Exploding Gas Tank

Myth: a car can explode when the gas tank is shot (original car capers episode summary)

Error according to viewers: they should have used tracer rounds, even though the Hollywood myth they were busting didn't involve tracer rounds. Tracer rounds contain phosphorous that glows when the bullet flies through the air.

Added note: tracer rounds are illegal... unless you can get the FBI to help out with your test.

New setup: They used .223 tracer rounds and shot into a gas tank at a firing range.

Results

Jamie unloaded a clip into the tank and couldn't get it to explode. Then four of them unloaded on the tank simultaneously and couldn't get it to explode.

Jamie decided the tank was too close and had the tank moved 50 ft back to give the phosphorous more time to ignite. This time, after several rounds, the tank ignited. It didn't explode, perhaps because the tank was riddled with holes, but the gas inside caught on fire.

confirmed (separate myth from the original, though)

Comments

Tracer rounds are not inheirently illegal. They may be in Kalifornia, but for the vast majority of the country, tracer rounds are perfectly fine.

Confirming Joe's comment.

The Myth is the phony explaination they give on how tracers work. The paint on the tip is only for identification. It has nothing to do with the function of the round.
http://en.wikipedia.org/wiki/Tracer_ammunition

I'm not sure I quite understand the running in the rain one. Are you testing how wet someone gets given a certain amount of time or distance? It is unlikely that anyone cares if running in rain gets them more wet per hour when undoubtedly the reason they are in the ran running in the first place is because they are traveling between shelters. BBC doesn't say running is actually worse, because in the scenario of the common myth--like running v. walking to your car from your house, the article clearly states that the faster you run the better. Time is a more powerful variable than speed in that running faster also decreases time spent in the rain, ie. the added wetness while running is more than compensated by the declining in time spent in the rain. Obviously, increasing the speed also decreases the time, which in turn decreases "total wetness."