Maybe I’m just too dense to figure this out….
In: Physics
Weight is a measure of the gravitational force. Assuming the balloon is near Earth’s surface, the weight depends only on the mass of the balloon (rubber and helium). Letting helium out decreases the total mass, and reduces the weight.
The other force at play here is the buoyant force. Assuming the balloon is in air, the buoyant force is equal to the weight of the displaced air. So buoyant force depends on the volume of the balloon. Letting helium out reduces the volume and so reduces the buoyant force.
At some point you will let out enough helium that the gravitational force exceeds the buoyant force and the balloon will no longer float.
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