Ava and the Neutrally buoyant balloons

Grandma Wilson had the chance to watch Ava last night, and I think they both loved it. They came back with balloons (which Ava thinks are just the coolest things all week). The problem was that these balloons were really good balloons, and kept floating up yo the ceiling (as good balloons are wont to do), so she was left alone on the ground reaching for them until her tall balloon retriever (me) could do his job and retrieve them for her once again.

(I know balloons can be a choking hazard if unattended, so I am attending very carefully)

I really like it when Ava can be as independent as possible. It's good for her to know that she can do things all by herself, and it's good for me to watch her grow and develop. So I decided I would apply some weights to the bottoms of the balloons in order to make them more easily retreivable by her should she accidentally let one go. I didn't want a super heavy weight--just something barely heavy enough to keep it from floating up, but not so heavy that it would drag it to the ground like a rock. In short, I wanted to try and make it "neutrally buoyant".

See, the reason that balloons float is not because they don't have any weight (measure one inside of a vacuum if you want to test that one--just have a really strong balloon that won't pop when the air pressure outside the balloon drops to zero), but rather because the air around them weighs more than the "air" (or helium) inside the balloon. If this is difficult to picture, think mixing oil and water. Oil rises to the top not because it doesn't have weight, but rather because it is less dense than the water. Same principle applies to balloons.

Anyway, I began thinking of materials I could use to try and get the balloons "just right" so that they neither float nor sank. I decided on duct tape, and let me tell you: I'm surprised by just how much a relatively small strip of duct tape actually weighs. It took only around 7 inches or so of duct tape to begin to sink the balloon. And as I began to refine the weight measurements, even a small piece, smaller than my baby fingernail would mean the difference between the balloon rising or sinking. Incredible to think about how much a difference a small piece of tape can make!

Ultimately, a balloon can never be 100% neutrally buoyant in practical situations, since air density varies with temperature, and the air towards the top of the ceiling will be less dense than the air near the floor (warmer, you know). But for all intents and purposes, we hit this one on the head, and Ava has been enjoying it all morning :)