Does A Tank With Fish In Weight More Than A Tank Without?

[roadmaster]

Have weighed fish to determine development by weighing a plastic container of water. Then place the fish in the plastic container and weigh again. Difference will be the weight of the fish. Works fairly well.

 

[P&J]

Consider this, though. . . You are standing in a fully enclosed box on a scale. If you jump, won't the reading on the scale go down? What's the difference between you in the air and a fish in the water?

-P

but, just before you jump, the weight shown on the scales, goes up, and also on landing. do you get heavier then? of course not. not to mention, its suggests tha something is weightless (without weight) unless its stood on a surface. its an interesting theory. just not related to the current discussion. or (to me) terribly logical.

are we really saying if you put a 20kg bit of wood in a tank, and it floats, it weighs nothing? plain and simple, the tank would weigh 20kg more, than before you put it in. there really is nothing to decide on. mass is mass, and that does not vanish, even in outer space.

Well, I was playing devil's advocate a bit, but I wasn't suggesting that your weight would change. Rather, I was referring to the weight of the box. If the BOX were on a scale and you jumped, what would happen?

I would be interested if anyone does this experiment with a bucket, though. I wouldn't be surprised either way.

How about another hypothetical? If you swim underneath someone in a pool, do you feel their weight as you go under?


-P

 

[Bridie]

Would imagine the density of a fish is higher than water, as dead fish sink to the ground rather than to float. Therefore if you add a fish and take out the volume of water it replaces, the tank will be slighty heavier while still containing the same volume.
A cat on the hood will increase the weight dramatically though

Pool question: I think the pressure a swimmer puts onto the water is distributed equally in all directions as water is a liquid. Therefore the waterpressure should be the same throughout a layer of water in the pool, of course depending on depth, as upper water layers are putting pressure on depper waterlayers. Very important question