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Clean babies are agreeable, but how efficient are they?

Just a few new pictures are up on Flickr, available here.

Last night, Punam and I bathed Dante; it took about half an hour. I couldn’t help but think that my surface area must be an order of magnitude greater than his (I outweigh him about 25:1), and it only takes me about seven or eight minutes to shower. Data, clearly, needed to be collected!

I settled on a simplified model of the body that would be a fairly close estimate and would only require seven measurements: Consider the torso and each limb as a cylinder, with length measured in the obvious way and circumference measured around the middle part (above the knee, below the elbow, at the bottom of the ribcage), then fit a sphere around the head (circumference measured as if for a hat). Here’s what I got, for Dante and for myself, in cm:

Multiplying each length by its corresponding circumference gives us the surface area of the cylindrical components. The head’s SA is just c²/π. Adding up the results, I estimate Dante’s surface at 6435cm² and mine at 37719cm² — just about six times greater. Dante (3.2kg) has a SA:mass ratio of 2011cm²/kg compared to 460 in my case, which underlines the commonplace that babies have to work a lot harder than adults to thermoregulate (roughly four times harder). But more importantly for our purposes, we learn that Dante’s totally factitious Bathing Efficiency Coefficient is 6435 cm²/30 min = 3.57cm²/sec against my 78.6cm²/sec, so we can conclude that bathing him is quite inefficient.

That said… we’re not going to skimp on it or anything. Clean babies are very nice to have around.

Edit: Forgot that each kind of limb comes in pairs. Doubled their contributions, updated numbers, point still intact.