Weighing fluids with immersed objects

[maxbashi]

So imagine that in an open room you have a big scale and on it you have a jar and a lid sitting next to each other. Imagine a butterfly floating into the jar but not touching the bottom. I wouldn't think this would increase the reading on the scale. But if you put the lid on the jar, closing the butterfly inside, would the reading on the scale increase (compared to when the lid was sitting next to the jar on the scale?) Would the butterfly be "pushing down" on the scale now?

 

[Curl]

Doesn't make too much difference if the lid is on. If there is air flowing to the bottom of the jar, the scale will pick it up. Look up impulse.