> > > If you place a small, live fish in a bucket of water, does this increase the weight over that of the bucket/water combination alone?
> > >
> > > My first response was to say "Yes" but then I thought about the displacement of the water and could not be so sure. What do you all think?
> > >
> > > Drac "Not to sharp on abstract problems" imaS
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> > If we assume that some water spills out of the bucket because it was full to the brim before adding the fish, then the fish will displace water equal to its volume from the bucket, and the change in weight will depend on the density of the fish compared to that of water. Since a fish has variable density which is usually close to equal that of water (as indicated by the fish's ability to stay in one place at various depths) I would assume that there would be essentially no change in the weight of the bucket. [...]
> >
> > Don
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> (-: This reasoning is otherwise impeccable in terms of known relations. The only quibble anyone could pick with the explanation is that a fish's body has greater density than water, so if you took a given volume of fish and an equal volume of water, the fish flesh weighs more than the water. The only reason that fish float in the first place is that they use a baglike sac filled with gas called a swim bladder, which they can regulate to give themselves "neutral buoyancy" when diving upwards or downwards.
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> Wolf "phish use physics" spirit

I had thought of including the swim bladder argument in my post (I am an aquarist, if that's a word, and have some experience with swim bladder problems with my fish-- Quite amusing sometimes, until they die.) Anyway, since the fish in the original problem was stated to be alive, I made the assumption that its swim bladder would not be empty, giving it a bulk density equal to that of water. (Unless, of course, the fish is weird and empties its swim bladder so that it can sink to the bottom and play "Rock". I have never known a fish to do this, though, no matter how much I encourage them.) I suspect, though, that even if the fish were dead, it would not necessarily be more dense than water-- Only one of my fish has ever sunk after dying, and that was one who had clearly had a swim bladder problem before his death. In general, I would stand by my statement that a live fish will have density (bulk density in this case) equal to water, but I will also postulate based on experience that if the fish were to die, it would be more likely to be less dense than water, and reduce the weight of the bucket/water/fish system as compared to the bucket/water system. I do welcome further discussion, however-- I find this subject very interesting! (You may have guessed that by the fact that I have replied more than once and my replies have been, for me, rather long...)

Don