Kevin's Watch

OK, so it's at least my current favorite show on TV, heh...

Anyone else seen it before? The show is pretty simple and a lot of fun. Basically they have two special effect engineering nerds try to recreate different myths and urban legends, like if you threw a penny off of the Empire State Building, it would kill someone. It's a very nerdy sciencey show, but it's awesome. And the two nerds who run the show are hilarious. A shame it's shown on a cable network at an odd time. I think it's on Discovery at, like, 9pm on Wednesdays. I usually forget when it's on myself.-jay

I've seen it a couple of times, I was particularly impressed with their card throwing machine, it didn't manage to seriously hurt anyone, but you should never underestimate a papercut!

Cool, Jay likes the Mythbusters! I'm a big fan of the show as well, and of the Discovery channel in general. It's entertaining and educational TV. I began watching the Mythbusters only a few months ago, and I've been hooked ever since. They've had too many strange and spectacular stunts for me to mention them all, but...

- It's neat when they test "Hollywood" myths, like the one where the movie bad guy gets blown backward across the room or through the window from the force of the bullet from the hero's gun. So the Mythbusters rigged up a dummy (made of a gelatin equivalent to the density of a human body) to be shot at by guns and rifles of increasing firepower. As it turned out, Buster didn't budge from any of the shots fired into him. In real world physics, bullets simply don't have enough energy to push a human body away, never mind sending it flying backwards. Myth BUSTED!

- A myth that turned out to be more than plausible and just a little disturbing was the infamous Chinese water torture test, where victims are strapped motionless while waterdrops fall relentlessly on the same area of their heads in regular, agonizing intervals. One of the show's crew volunteered to be tied down on a rack while water dripped onto her forehead. Her head was held in a metal brace so she could not move her face away from the dripping water. She was able to endure the "water torture" for about an hour or so before it proved too much to bear. Even though she wasn't a prisoner in a dungeon but rather was in a brightly lit studio surrounded by her colleagues, that did not prevent the water torture test from messing with her mind. The Mythbusters took this experiment very seriously, hiring an emergency medical team to monitor her condition. It was a little freaky seeing how the torture test eroded her will.

(Hey, don't get any funny ideas, Jay...)

I've seen several episodes. I like the myth about the "Elevator of Death"
The story goes that a woman survived an elevator drop that fell 7 stories.
The Mythbusters rigged an elevator with their gelatinous friend, "Buster" inside
and dropped the elevator (minus cables) down a shaft in a building.
Could a person jump up at the last second to cushion the impact?
Not really. "Buster" was demolished, as well was the elevator car.

The rest of the story of the woman who survived was told
after the experiment was completed.
The elevator shaft was a tight fit around the car that busted from the cables,
thus building an air-cushion beneath the falling elevator.
Also, the broken cable (dangling under) coiled in the shaft as it fell with the elevator,
making another cushion for the elevator car to land on.
The woman did live, although banged up quite a bit.

Also check out the radio-controlled jet-propelled car episode that they made to bust a myth.
Mounted on top of a car was 3 or 4 JATOs (Jet Assisted Take Off rockets used on airplanes)
Will the car fly? You'll have to see the show to find out.

I love Mythbusters, but sometimes their logic is a bit flawed (see the Goldfish memory experiment).

Seen a couple of episodes here and there, thoroughly enjoyed.

Matrixman wrote:In real world physics, bullets simply don't have enough energy to push a human body away, never mind sending it flying backwards.

Any idea of the specifics of this one? i.e. Calibres, bullet types? Reason I ask is that I've seen animals bowled over when shot, and can't see why it wouldn't apply to people as well. Of course, the ammo used is not something you'd usually find in your average policeman's or soldiers gun.

--A

Sorry, Avatar, I'm not that familiar with the terminology around firearms (and I don't think I want to be familiar with it, heh). But if I happen to catch that episode again, I'll try to pay more attention to the guns they were using.

No worries, knew it was a shot in the dark.

Might have something to do with the composition of the dummy as well. Bodies are variable in their density, which affects ballistic behaviour "inside" them, as it were, and that's just one possible factor I can think of offhand.

--Avatar

No worries, knew it was a shot in the dark.

Argh!

Anyway, I'd heard that some types of guns are used specifically because they're good for knocking people down (like colt .45s).

From a physics viewpoint I'd have thought that if a bullet stops before it gets out of the other side of the body then all its momentum must be transferred to the body.

Now, a colt .45 bullet is quoted as travelling at a little under 1000 feet per second (why people still use archaic measurements like this I have no idea) which is equivalent to 300metres/s. The bullet has a mass of 0.0115 as far as I can tell. It seems they insist on using all kinds of obscure measurements when talking about guns (who measures anything in grains?). This would give it a momentum of 0.0115x300=3.45kgm/s

This would cause a human body of mass 80kg (the average) to be knocked backwards at a velocity of 3.45/80=0.043125m/s.

Apparently I have wasted my time though, because I have no idea how quickly the momentum is transferred from the bullet or how much force is required to knock a human over, the internet is unhelpful in this regard, when it served me so well up to now. If anyone else can carry on from here I'd be very grateful.

The only things measured in "grains" are bullets as far as I know.

1000 fps is pretty slow when it comes to bullets. Average muzzle velocity for hunting big game is around 2,200-2,700 feet per second, and accepted wisdom is that heavier bullets, at slower speeds, are more effective. However, the dynamics of rifle wounds are far different to those of pistol wounds, partly for that very reason.

A 147gr .357 Magnum bullet delivers 450 foot pounds of kinetic energy. That's equivalent to being hit by a baseball bat travelling at 210m/ph.

Having done a little research on this, (because I've come across serious conflicting opinions on the matter), it seems that the answer is in the transfer of kinetic energy from the bullet, to the body of the target. The bigger and heavier the bullet, the more force is delivered.

It's by no means a certainty that anything hit by a bullet like that (300gr is about the biggest you can use) will be knocked back, but it's a clear possibility.

Of course, as I said earlier, it's not the sort of load you're going to find in a policeman's gun though.

--Avatar

I saw that episode, and they busted the bullet thing pretty convincingly. They used bullets of all sorts of different callibers and from different guns and rifles, and none of them moved the dummy even a millimeter.-jay

I think they're overestimating how easily the bullets pass through the human body. What if it hits a bone or an organ? Then the energy from the bullet has to be transferred to the body. I was reading about the colt .45 which was designed to "knock even a heavy man back". How could the army be so wrong? Surely they tested it?

Nathan wrote:I think they're overestimating how easily the bullets pass through the human body. What if it hits a bone or an organ? Then the energy from the bullet has to be transferred to the body. I was reading about the colt .45 which was designed to "knock even a heavy man back". How could the army be so wrong? Surely they tested it?

Because bullet's transfer energy as soon as they enter the body; they don't need to transfer it to bones or organs.

Loremaster wrote:I love Mythbusters, but sometimes their logic is a bit flawed (see the Goldfish memory experiment).

I caught that episode today. The guys talked to some professor of psychology or something, and he said their experiment was a valid way of testing memory. Their test seemed okay to me, but then again I'm lousy when it comes to analyzing the soundness of experiments (I wasn't the quickest mind in my science class, heh), so maybe you could explain what you mean by their flawed logic?

Because bullet's transfer energy as soon as they enter the body; they don't need to transfer it to bones or organs.

Not if it goes right through and out the other side.

Nathan's right there. High speed projectiles pass through the body, and transfer the majority of their energy into whatever is behind the body.

A famous hunter, on this very question, offered this example: Take a standard bag of oats, and stab it, as hard as you can, with a knitting needle. The needle penetrates the bag easily, and doesn't move it at all. Take the same bag, and stab it with a walking-stick, using the same force. You'll knock the bag over.

Surface area, i.e. the size of the bullet, is a major factor, as is the speed, weight, shape, angle of penetration, etc. (That's why it's only a possibility, never a certainty.)

Another factor is that ballistic gel is only the closest approximation that they can make to human density. As was so rightly pointed out, there is nothing inside it of differing density.

If the bullet penetrates cleanly, and exits the other side, the majority of the force remains with the bullet. Hence the necessity of a (relatively) slow moving projectile. If it does not exit the body, all kinetic energy is transfered from the bullet to the target. If it's the type of force I mentioned earlier, 450 ft lbs of force, I find it all too easy to imagine that a person could be knocked over.

Anyway, working as I do, for, and with, serious hunters, and not only having been assured that they have personally witnessed incidences of animals knocked backward when shot, but having seen it on film myself, I'm pretty convinced that it happens.

Again, much depends on many variables, up to and including the stance and weight of what you're shooting. Muzzle velocity, bullet weight, and the force exerted by the impact all play a role.

What were the parameters of the experiment? Was the target "human" shaped, affecting it's centre of gravity? I can't imagine ballistic gel, with the depth of a human torso, stopping even a light load.

Did the bullets fully penetrate the target? If so, there's your answer straight away. Whatever energy was carried by the bullet expended itself in the backstop, whatever it was.

--Avatar

That's the one problem with Mythbusters - they tend to ignore some variables. Evidence: see the story about the sinking ship sucking people down. They say ships don't, but documents state that they do.

Dude, all you have to do is watch "Titanic" to know that's true......

They did one to test whether vibrations could cause a bridge to oscillate (as with the Tahoma narrows bridge and the millenium bridge) then claimed the myth busted when they couldn't get it to work with their shoddy bridge and crappy vibration generator.

They lose credibility in my book because they claim myths busted when they haven't properly tested them.

Wouldn't busting a myth be the same as proving it's true, and therefore, not a myth at all? And yet, they seem to be going out of their way to prove it was indeed a myth after all. I find this to be too confusing.