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Name: betty a laliberte
Status: N/A
Age: N/A
Location: N/A
Country: N/A
Date: Around 1995


Question:
We want to learn how much skin our classmate Steve has. We have been thinking of dividing the body into geometric shapes. Our problem is that the body seems to be oddly shaped. We have tried calling doctors and nurses, but they are not too interested in our problem. Would you help?


Replies:
The point of the question is not the numerical answer. It is, how do you go about finding the answer? I think that the question is a very good one, it is designed to get you to THINK (not just repeat someone else's answer), and I encourage you to explore possible answers with each other. In the meantime, please congratulate your teacher for me.

jlu


That IS an interesting problem! I do not know exactly how to approach it. It may keep me up all night. One thought I have is that you might be able to exploit similarity somehow. If you can find a toy model (e.g. a "Ken" doll or a GI Joe) that is approximately similar to Steve, then if you can answer the question about the doll you can use ideas of similarity to estimate an answer for Steve.

The advantage of this would be that you can perform experiments on the doll that Steve might object to (e.g. wrap it in silly putty). I expect it would be easy to find Steve's volume that way. Surface area will require more creativity. What could you do with a photo of Steve?

chaffer


Well, this is essentially a problem in "surveying." How do surveyors figure out distances and areas etc.? You need to set up some kind of grid or collection of points on the body, in between which the surface is close to flat. The other option, of course, is the physicists approach - assume Steve's surface is fractal, estimate fractal dimension, calculate a lower bound from his volume (and the surface area of a sphere of the same volume) and go from there. (The surface area of a fractal body like that should be infinite so you will have to cut it off at some practical dimension - say the size of a finger, or maybe the width of his hairs - assuming you were planning on counting his hairs, right?)

asmith


1) Cover him with triangles or some other regular figures. If the figures are small enough (and the guy is smooth) you will get a good approximation to his surface areal by adding the areas of the figures that cover him.

2) If you like to be more physical, you can cover him with paint; make sure the layer is equally thick everywhere. Divide the volume of paint used by the thickness of the paint layer - this ought to be the surface area or a fair approximation.

jan


My son had a different idea that I thought was workable. Approximate Steve's body with a bunch of solid shapes for which you know surface area formulas (cylinders, spheres, and so forth). For example, his head might be spherical of ellipsoidal, his neck a cylinder, etc.

chaffer


Problem 27 on page 832 of CALCULUS (3e) by D. G. Zill quotes the approxima- tion in terms of weight, w, and height, h, as
S = 0.1091*(w**0.425)*(h**0.725). Worth a try!?

tee



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