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Identifying Materials Using Archimedes' Principle.

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awemawson:
Scrap value of ones and twos is peanuts. A big heap makes analysis worthwhile hence the question. If your back garden is piled 10 foot high in scrap disk chassis I'll lend you the analyser to sort through them, but I very much doubt that it is!

When I moved 7 years ago I had accumulated a big pile of alloys that I had cast to ingot for convenience. (Mainly the chassis from several Dataproducts line printers) - rather than strap up yet another pallet to move I sold it all (for a very good price) rationalising that I could thus afford to buy ingots of the specific alloy that I wanted when I set up the furnace again.

SwarfnStuff:
Ha, thanks for the physics revision. Back down the deep dark recesses among the cobwebs among my grey matter. You were right, I skipped to the answer (final line) of the algebra. Amazing just what stuff we learned actually does come in handy later in life - just have to recall it though.
John B

vtsteam:
I recently read an article in a woodland management magazine written by a guy who was trying to calculate what tha actual volume of wood was in a cord, minus the air. He went to great lengths trying different methods to calculate it based on measurements, estimations of volumes and densities of diffeent wood species, etc. He still wasn't satisfied with his own answer.

I was tempted to write in and suggest he take a sample of say 8 cubic feet stacked, and then immerse the pieces individually in a graduated tub, to get the exact volume of each irregular piece add them together and divide by 8 to get the wood volume per cubic foot of stack. but figured it was too much trouble to write to a magazine. So here it is, courtesy of Pete, anyway!  :)

DavidA:
I'm probably being a bit dim here.

How does this apply to materials that have a SG greater than 1 ?

I.e.  materials that sink.

If the object has a volume of,  say,  100 cc and it is made of steel then it will sink and displace water similar to an object of the same volume made of brass.

This kind of problem usually goes back to Archimedes and the kings crown.

But that was a straight forward matter of weight and displaced water volume of a known material,  gold, and what  ever the crown was made out of.

Dave.

vtsteam:
David, whatever the object weighs, divded by its submerged displaced volume gives the mean density of the object.

For objects with density greater than water, you can just let it sink on its own. For objects less dense than water, you have to hold them under.

Displacement in naval architecture is a little different. It is the weight of a volume of water displaced by a floating object. The displaced volume is affected by the density of the water (salt vs fresh for instance), because the relative density of the object and the water determine how deeply it sets. Displacement does not vary between fresh water and salt, though displaced volume does, because displacement in this field is expressed as weight.

When objects are completely submerged, the conventional displacement is always equal to the volume of the object, no  matter what the relative densities are. So it's very handy for determining the volume of irregular objects.

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