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Name: Michelle
Status: student
Grade: 6-8
Location: CA
Country: N/A
Date: 12/15/2005


Question:
How can I explain why the human body will not sink by using numbers that describe density? I learned that the Dead Sea is 33% salt. I also learned that the average density of the human body is 61-67 with breath exhaled. I don't know what unit this is in. And I don't know how to compare the two.


Replies:
Hi Michelle,

Actually, some human bodies will sink. Some, including championship swimmers, will sink, because of their low body fat content (fat is less dense than muscle).

The best way to compare among things is via specific gravity- the ratio of something's density to that of pure fresh water (which is about 1g/ml or 1kg/L).

The Dead Sea is 33% salt by mass, i.e. 1kg of Dead Sea water has about 330g of salt, but that still doesn't tell you density (you would need to know the volume of the 1kg of Dead sea water). A recent article (2002) states the density around 1.17 kg/L.

http://www.limnology.org/news/silnews35.pdf

The 61-67 for the human body is in pounds per cubic foot. Convert to kg/L and you will have everything in the same basis.

Don



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