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        riddles >> easy >> surface area measurement
        
(Message started by: jabhiji on Aug 27^th, 2003, 5:58pm)

Title: surface area measurement
Post by jabhiji on Aug 27^th, 2003, 5:58pm

Is there some practical and accurate way to measure the surface area of a finite, odd shaped object (say the human hand up to the wrist) ? In school, they taught us to measure volumes by immersion in water....seeing how much flows out and stuff.....but I can't think of how to measure the area.

Title: Re: surface area measurement
Post by SWF on Aug 27^th, 2003, 6:10pm

There are many ways. A couple of the more practical that come to mind:

If you have an accurate scale, weigh piece of paper to figure out how much it weight per unit area. Cut out the tracing of your hand and weigh it. Then you can figure it out.

Scan the picture of the traced shape into your computer with a scanner. Fill in the area with image editing software. Then use the software to find out what fraction of the area is covered by the filled in color. That is roughly what I do, although I had to write a simple program to count how much of the area is covered, since my scanner software doesn't do it.

Title: Re: surface area measurement
Post by Icarus on Aug 27^th, 2003, 7:30pm

Another means is to find a liquid substance that binds to the object being measured in a uniform layer. There are a number of possibilities. Some oils will work if the process is done carefully. Paints will often work even better.

Measure the volume of the oil before and after dipping the object in it. Divide the difference by the thickness of the layer.

To determine the thickness of the layer, do the same thing with another object whose area is known. Divide the volume obtained by the area.

It is important that the film be uniform, so there are some limitations to the accuracy of this method. But then SWF's methods only work for flat surfaces (be warned here that I use "flat" in the differential geometric sense: you can't bend a piece of paper to match it, not even for a small section.)