# How would you measure the volume of a human body?

So I’m chatting with brianjedi and Flymaster, and, of course, the conversation turns to Aaron. (I swear brianjedi asked about him first.) Brian asked Aaron’s volume. I answered 26 lbs. before he clarified that he was not looking for weight, he was looking for volume.

Now, I’m not a physics genius by any stretch of the imagination. All I know about physics is if I drop something on my foot, it’s gonna hurt. I assumed I could use the Archimedian principle, but Flymaster pointed out that humans float. We discussed the possibility of using alcohol instead of water, but the less said about that, the better.

So, assuming the subject ever comes up in conversation, how do you figure out the volume of a human being?

Robin

Oh, and #straightdope on Undernet IRC is not affiliated with the SDMB, the Chicago Reader, any admin, mod, member, or any other human being or entity in the known universe.

Robin

Also, I want to be sure that it’s clear that I understand you could get the volume of an adult by telling him to swim to the bottom of the pool. But with a baby, is the best you could do just spiking him on in there, and measuring before he bobs to the surface?

My thought was building a synthetic Aaron out of that ballistics gel stuff like they use on “Mythbusters” all the time.

Well, sure, people float, but most people can force themselves to stay completely underwater, especially if they have something to push on, like a swimming pool ladder.

I can think of some other solutions, but they’re gross and would call for unnecessary bloodshed.

1. Fill bathtub to rim.

2. Insert person.

3. Capture water that flows over the rim.

4. Measure volume of water.

Arranging the appropriate plumbing hookup and capture of the spilled water is left as an exercice for the reader.

No, you just fill the container complete full of water, drop the tyke in, pull him out, and measure the amount of water that was dumped out. You could then refill the water, dunk your hands in, and subtract that amount to be as accuate as possible.

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|____________________|

\| | | | | | | | | | /<----water splashing out
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|         | |        |
|         | |        |
|      \  | |    /   | <---your hand + Aaron
|     O->------<     |
|      /         \   |
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|____________________|

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|                    |  }---volume of Aaron + your hands
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|~~~~~~~~~~~~~~~~~~~~| <--------new level
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|____________________|
\| | | | | | | | | | /<----water splashing out
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|         | |        |
|         | |        | <---- just your hand
|         | |        |
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|____________________|

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|____________________|

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As Sunspace said, but do a previous run with just putting your arms up to a determined point. That way, when putting in the baby, you can use your arms to that same point to support him, and subtract that amount of the answer.

If you cannot capture the water coming over, you could do it by weight, since water is unifrom density. Weigh one gallon of water. Now find a big barrel. Fill it with water and weigh it. Now put the baby and your arms in, to the same pre-determined point. Take out the baby and your arms. Measure the weight of the barrel and the remaining water. Now you know the weight of the water you displace. You have weighed one gallon of water and seen what that weighs. A little quick math gives you the answer.

How accurately do you need to know it. A person who weighs 62.4 lb. will have a volume of just a few in[sup]3* more than 1 ft[sup]3*.

If I float on my back in a still swimming pool just my face to about my ears is out of the water. When I breath out I start to sink and when I breath in I rise again. My overall specific gravity is very nearly 1.

Way to go Simmons!! Beautiful coding. Gives you a lot of confidence in the answer, doesn’t it?

For that matter, why is the overflow part necessary?
[ul][li]Partly fill a large sink[/li][li]Let the water settle[/li][li]Mark the level against the inner wall of the sink with a grease-pencil or piece of tape[/li][li]Hold baby underwater[/li][li]Mark the new elevated level of the water, after settling[/li][li]Remove baby from sink (administer CPR, call 911 as necessary)[/li][li]Measure difference between marks, in centimeters[/li][li]Measure square area of sink, in centimeters[/li][li]Multiply area of sink and difference in depth to obtain a total number of cubic centimeters equal to the volume of baby.[/ul][/li]
A cinch, with no mopping required.

Um, who’s Aaron?

In lieu of drowning your baby, you could find the volume by approximating your baba as five cylinders (limbs+torso) and a sphere (head). And they say engineers have no regard for human life…

You you could pinch one of those 3-D laser scanners that converts objects to computer models. Might be a bit difficult with a squirming baby.

[lame hijack]
The fact that it will fall on, and exert a force on, your foot is physics. The fact that this hurts is biology.
[/lame hijack]

Aaron is Baby Doors; my and Airman Doors’ son. He’s also the first Thoroughbred Doper, since Airman and I met on the SDMB.

Robin

By consulting statistical data about the density of humans.

From this page, the average density of “flesh, human” is 61-67 pounds per cubic foot.

If Aaron is 26 lbs, that’s about 0.4 of a cubic foot, or 691 cubic inches.

That’s about what we finally figured up, Jpeg. I found a stat for average density and figured it up.

Still think the “wrap Aaron in Saran Wrap and dunk him in alcohol” theory would be the best. Dangerous, though.

Just in case anyone wants to do the measurement themselves, I should point out that you don’t need to capture and measure the overflow for the ‘submersion in a filled tub’ method, or calculate the precise shape of the tub for the ‘mark lines on the side method’.
Just submerge the baby and make a mark where the water level is (overflow line is convenient and avoids having to mark the tub). Remove baby, CPR, etc. Now just fill the tub back up to the line, measureing the amount of water you put in. That gives you volume.

And, by the way, accurately measureing a person’s volume is regularly used to calculate body fat percentage for high-tech athletic evaluations. They use submersion methods.

Access to the [url=http://www.bodpod.com/]bodpod is what you need. It uses air displacement so you wouldn’t hafta worry about those pesky child endangerment laws…

As Archimedes said, “Eureka!”

(I’m late chiming in, but someone had to say it)