7.26.2008

two science q's

I have two questions for you science-y types out there. I can't find a good way to Google or Wikipedia this, and asking wmtc readers is my third choice for random factual information.

1. It is said that if you throw a coin from a great height, it picks up so much force as it falls, that it can do great damage. Where I grew up, we heard that if you threw a penny off the Empire State Building, it would bore straight through someone's skull into their brain and kill them.

If this is true, why do raindrops not bore into our skin? Rain is falling from a great height. Is it because rain is liquid so it has different properties? Then shouldn't hail kill us?

Or maybe that old story is not true?

2. Long ago, people believed in the spontaneous generation of life. The example I remember is that flies arose from rotten fruit, or that spoiled meat gave rise to maggots. Now we know that is not true.

So where do the maggots come from? (From other maggots, yes.) I mean, specifically, when a piece of flesh is rotting - whether it be a creature's untended wound or a dead animal - maggots appear and contribute to the process of decomposition. Where do the maggots come from? Where were they before? How did they "know" there was rotten meat to be eaten? Where do they go when they're finished? Why do we only see them when they are writhing around a piece of dead flesh?

19 comments:

impudent strumpet said...

Maybe because the coin is exponentially heavier than the raindrop? Maybe because the raindrops change shape when they hit us but the coin doesn't, so that lessens the impact somehow? (Once upon a time I could actually describe these concepts in big grownup sciency words.)

I seem to have a lot of ideas about maggots, but I have no idea why I know any of this and I'm too squeamish to google up confirmation:

I think maggots are fly larvae and they come from eggs laid by flies. For whatever reason, an open wound is a nice appealing environment for flies to lay their eggs in (and I think maybe feces is a similarly appealing environment). So if you keep a wound clean and covered (and/or you're in a clean indoor environment where there aren't any flies) the maggots either won't get in there in the first place or will get cleaned out when the wound is cleaned.

But I have no idea why I presume to know this so it may be completely wrong.

Toma said...

The answer to the coin question has probably been answered by these guys here: http://dsc.discovery.com/fansites/mythbusters/mythbusters.html. They have proven and busted a lot of those types of myths. If they haven't done this one yet, maybe we should ask them.

And while there, they could probably have their science crew investigate the maggot question too.

Wes said...

A penny dropped from the Empire State Building won't kill anyone or bore through anything. This is because the terminal velocity of a penny (let's assume US currency since that's the mass upon which all of the experiments have been based) is unstable and has only been measured at approximately 45-65mph. At that speed, it takes a brick-sized object to do serious damage (consider that baseball players are routinely smacked with much heavier objects traveling at up to twice that speed). MythBusters (excellent show) did this, and found it'd take a speed of roughly Mach 3 to do serious damage to a skull with a skillfully-fired penny.

Sources:
Berkeley Science Review
Empire State Building, In Popular Culture, Wikipedia

M@ said...

The coin thing I think comes from back-of-the-napkin calculation of the gravitational force on the penny. Acceleration in gravity is 10m/s/s, so by the time it falls the 1000 feet or so, it's travelling so fast that the momentum gives it a huge force of impact.

I think that it's untrue because of the other factor: wind resistance (or air resistance). Wind resistance increases as the body increases in speed, resulting in a terminal velocity at some early point, beyond which the penny picks up no more speed (and therefore no more momentum) no matter how far it falls.

As for the maggots, yes, flies lay their eggs in the food source to give them a good healthy upbringing.

Interesting sidenote on maggots (which, I assure you, creep me out to no end -- I don't exactly go looking for maggot-related sidenotes). In the early 19th century (possibly earlier, I'm not sure), it was common for army "doctors" to carry with them a tin containing a few maggots. When a soldier got burned or wounded, the doctor would bandage the injured flesh with the maggot inside.

Because maggots only feed on dead flesh, they would basically clean out the wounded flesh and leave the nice, clean live flesh behind. Much lower risk of infection and pretty much the only way to treat burns at the time.

I said it was interesting. I never said it wasn't totally disgusting. Probably saved a lot of lives at the time though.

James said...

1 - The whole coin thing is a myth, as folks have said. Further, rain drops spread out as they fall, which gives them more surface area, which means they slow down even more from air resistance. Falling raindrops don't have the iconic teardrop shape -- they're more like little spheres with flat bottoms, but under some circumstances, they can even take on parachute shapes.

2 - The maggots come from fly eggs, laid by flies which land on the meat. This page has a good write-up on the research that established this in the 17th-19th centuries.

evilscientist said...

Maggots are the larval form of flies. Flies lay their eggs on dead or decaying meat, the eggs hatch into maggots. The maggots eventually pupate into flies and the cycle continues.

Kim_in_TO said...

Without taking any time to look up facts, flies also lay their eggs really fast - so you may not notice them doing their work. Later, when the maggots appear, it seems as though they have come from nowhere.

neutron said...

These look like some pretty good explanations. Just to add to what wes said, terminal velocity is the fastest possible speed an object can travel due to gravitational pull.

As an aside, max speed means zero acceleration. Zero acceleration means force equilibrium and that is to say that gravity force = drag force.

James said...

Because maggots only feed on dead flesh, they would basically clean out the wounded flesh and leave the nice, clean live flesh behind. Much lower risk of infection and pretty much the only way to treat burns at the time.

This went out of fasion for a long time, but it's been revived recently; it's actually an excellent way of dealing with necrotic flesh in a wound.

Just to add to what wes said, terminal velocity is the fastest possible speed an object can travel due to gravitational pull.

...in a given medium at a certain temperature/pressure/etc. Terminal velocity is the speed where the force of gravity is balanced by the force of drag. This is different from escape velocity, which is the speed that would be reached by an object falling from infinity, abscent any atmospheric drag. (It's also the speed you'd need to be going to get from the surface to out beyond orbit, which is where the name comes from).

Terminal velocity depends on what planet you're on, how thick the atmosphere/hydrosphere is, and the shape of the falling object; escape velocity only depends on what planet you're on.

L-girl said...

Hey, thanks for the answers, everyone!

How interesting that the penny thing is a myth, as I suspected it might be. I wonder how many people of my generation believe that.

Neutron and James, you're now way beyond what I can follow without glazing over, but hey, knock yourselves out.

This went out of fasion for a long time, but it's been revived recently; it's actually an excellent way of dealing with necrotic flesh in a wound.

Some doctors are using leeches again - albeit not as Theodoric of York did, to bleed a patient to death. I'm sure there are many examples of old knowledge being recycled and updated into modern useage.

L-girl said...

(consider that baseball players are routinely smacked with much heavier objects traveling at up to twice that speed).

But not from such a height. As M@ points out, it was the height that was key in that myth.

L-girl said...

Without taking any time to look up facts, flies also lay their eggs really fast - so you may not notice them doing their work. Later, when the maggots appear, it seems as though they have come from nowhere.

I think that's the key here.

Plus I didn't even know maggots were fly larvae. I thought they were worms.

I have a horrible mental image of something I once saw involving a tremendous number of maggots. I will not describe it, as it will make you all puke. I feel my stomach clenching and turning as I think of it.

Sorry.

Ugh.

James said...

The Straight Dope covered the raindrop question a few months back. It's the second question on the page linked to above.

James said...

The maggot life cycle is very useful in forensic investigations, because the time it takes for the flies to lay their eggs, the eggs to hatch into maggots, and the maggots to go through the stages of their life cycle is reasonably predictable. (This is why the character Grissom from CSI is an entomologist.)

The books Stiff by Mary Roach and Corpse by Jessica Snyder Sachs both have good discussions of the research being done on this.

L-girl said...

That's very interesting!

Which also reminds me to say, thanks for the links, everyone.

Jen said...

I was thinking about this on the dog walk today (picking up poo will do that). I was wondering: I know you don't watch heaps of TV and your reading leads more to non-fiction, but I'm surprised that you've missed that ol' mystery/ forensic chestnut, the entomological dating of time of death. You can tell how long something's been dead by the maturity of the fly and other flesh eating bug life cycles. The wikipedia entry is very detailed (including movies in which forensic entomology is a key feature).

L-girl said...

I do read a lot of fiction, but it skews to the literary side, not a lot of murder and forensics going on.

My only experience with time-of-death stuff is from my former Law & Order addiction. But on that show, they never said how they knew the time of death! It would just be things like, "From the looks of things, I'd say she died between midnight and 5:00 a.m.". Never any mention of maggots!

James (above) mentions CSI in this regard.

The wikipedia entry is very detailed (including movies in which forensic entomology is a key feature).

Wiki entry on...?

James said...

But on that show, they never said how they knew the time of death!

In Corpse (mentioned above), Jessica Snyder Sachs points out that it's really pretty much impossible to determine time of death to the accuracy seen in TV crime shows, short of having someone who saw the person alive 10 minutes before someone found the body. Forensic entymology helps, but is only accurate to within several hours.

L-girl said...

Forensic entymology helps, but is only accurate to within several hours.

In that case, L&O was very accurate. They would always put it within a few hours, and the examiner would say she couldn't be more accurate than that. Especially what with the water, and the rats...