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

[saz326]

Imagine a decorated tank full of water.
Does it weigh more when fish are added - even when they are swimming around..?

Surely when fish are swimming they are supporting their own weight..
..but then there are forces acting on the water...
... I dont know

...does the tank get heavier if they all sit on the substrate? Thats another question

Cant get the poll to work.... Just ideas then please people.

 

[raptorrex]

Imagine a decorated tank full of water.
Does it weigh more when fish are added - even when they are swimming around..?

Surely when fish are swimming they are supporting their own weight..
..but then there are forces acting on the water...
... I dont know

...does the tank get heavier if they all sit on the substrate? Thats another question

Cant get the poll to work.... Just ideas then please people.

as long as fish are in the tank, their weight bears on the tank and stand. and no, it will be the same weight if the fish is, swimming, as if it is at rest, on the substrate..

 

[MOW4T]

very much doubt it as the size of the fish would displace water. so depends if the "whatever" weight of the fish is more than the displaced water but even if it was it wouldnt be noticable

 

[raptorrex]

very much doubt it as the size of the fish would displace water. so depends if the "whatever" weight of the fish is more than the displaced water but even if it was it wouldnt be noticable

only if the, water, it displaces, is removed. which it is not in hobby tanks. good answer though

 

[Kaidonni]

There'd definitely be more mass in there, but mass is different to weight. Yes, I'm being a regular 'Stephen Fishing' . Any spare trout around to hit me with?

PS: My forename is actually Andrew.

 

[Peggers]

Most fish seem to sink when they die so I'd say that the mass of the fish is more than the water it displaces, assuming the water was filled to the same point in both tanks then the tank would get very marginally heavier. Where the fish is in the tank wouldn't change the overall weight.

 

[Truck]

The Mass of the fish is always more than the water it displaces otherwise it would float at the surface 24/7, but the fish can regulate the amount of ballast in the swim bladder which helps it maintain it's position in the water column, to answer the OQ, yes a tank does have a higher mass with fish than that without.

 

[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

 

[OohFeeshy]

Ah, yes, but just before you actually get airbourne the scales will go up because you've pushed down on them in order to jump. The amount it goes up is the same amount it goes down.

Simialrly with fish, they're pushing down on the water in order to stay in it. Er. It's difficult to explain. Imagine a similar situation with birds- in order to fly, they use their wings to push down on the air with a force equal to that of gravity. The downward force would mean that the weight of the tank would be the same whether the bird was standing on the bottom, or flying.

 

[saz326]

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

.. I think I love you! Great answer.

'Mythbusters' did a similar thing to this with birds in the back of a lorry. Was a good epoisode.

Im half convinced - but still half unsure. Maybe if I scale it up to an aquarium with a whale in it...? Nah - that doesnt help.

 

[Ryandsimmons]

The fish is pushing down on the water to stay floating.

Imagine you are holding yourself on a wall to stay above the ground. The wall is pushing down on the ground with both it's weight and yours. The water in the tank is doing the same.

So yes the tank does weigh more with the fish in.

Try this:

Get a bowl.

Put it on a scale.

Fill it 3/4 of the way with water.

Check the weight

Put an orange in the bowl, it will float.

Check the weight. It will be bowl + water + orange.

 

[raptorrex]

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.

 

[OohFeeshy]

mass is mass, and that does not vanish, even in outer space.

Unless you count converting mass to energy, of course...

 

[loachman]

If you add something to the tank, and don't remove anything, the mass goes up. Weight is just mass times gravity (a constant), so it also goes up. It doesn't matter what you add, or whether it floats or not.

The only way it wouldn't is if you removed a volume of water equal to the volume of the fish, then the change would be negligible. Fish weighs a little bit more than the water they displace (they don't float), but not by much. And not by enough you could readily measure it.

 

[Dave Spencer]

mass is mass, and that does not vanish, even in outer space.

Unless you count converting mass to energy, of course...

Mass and energy are interchangeable. Neither can be destroyed.

Of course the tank weighs more with fish in.