Maybe I’m just too dense to figure this out….
In: Physics
The balloon gets lighter. But I think you need to compare this to other things based on the same principle: boats and hot air balloons.
Keep in mind that a hot air balloon used to lift people off the ground is also VERY heavy. Adding hot air to it doesn’t change that. What matters is that the weight of the air it displaces is more than the balloon’s (plus the basket and riders) weight, so it floats.
When the weight of a boat is less than the weight of the water it’s displaced, the boat floats. If the boat shrinks a LOT but weight ”slightly” less, it will have a net sinking effect because it’s displaced less water, but not enough to make up for the weight reduction.
A small helium balloon shrinks and gets lighter, but now the ratio of weight to the balloon’s rubber to helium goes in favour of the balloon rubber which is much heavier than air. The balloon will begin to sink, or at least not float as easily.
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