I was wondering?????

Question

if i had an aquarium that weighed 50kg when filled with water and i added a 2kg fish that did not rest and was constantly swimming

would it add to the weight of the aquarium

Answer 1

Yes. Gravity is acting on all mass: the tank, the water

the fish,etc. Place the tank on a sensitive scale with

(and without) the fish. See the difference? By the way,

good size fish: 2kg fish weighs 4.4 pounds.

Answer 2

yes.

let's take a silly example.

suppose they were really big fish, and raised the water level by 1/2.

since they are neutrally buoyant, it's just like they were water.

so now the tank would weigh 75 Kg.

now i know you're thinking of little fish, so they wouldn't increase the weight that much.

but they would increase the weight proportional to their volume or weight.

BUT, it gets even worse.

suppose you were to put a balloon in the tank.

yes, it'd float.

but suppose you held it under water.

if you did that, the amount of force you expended to hold the balloon under water would cause an increase in the weight that the water exerted on the bottom of the tank.