> The one I want to have your view points is one that I could test if I just would. Question:
>
> 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

That depends on a particular assumption. If we assume that the bucket is not filled to the brim (such that the fish's entry would spill some water out of the bucket) then all that changes is you add the mass of the fish to the system. Yes, the fish does displace some water, but the fish still exerts a downward force equal to its mass times the acceleration due to gravity on either the water beneath it or the bottom of the bucket (depending on what it chooses to contact) and the remaining water that it displaced is still there exerting its dowmward force. All of those forces must be counterbalanced to lift the bucket (or to hold it still on a scale) and since "weight" is simply the downward forces an object exerts on whatever is supporting it, then yes, the weight of the whole thing is higher compared to the weight of the bucket and water alone.

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.

So there you have it, for two different scenarios (unspecified by the question.) I wonder how many people actually think I'm any good at explaining this stuff in my hurried, verbose fashion... Maybe that should be the next Reader Poll. :-)

Don