Okay, fast thought experiment. Take a person, put him in scuba gear (so he won't suffocate) and then lock him in a big airtight plastic baggie. Put the plastic baggie on the scale. It's a /big/ scale, so none of the baggie is hanging off of the sides of the scale. The person's feet, for example, contact the scale just through the plastic.

Now the person jumps. (The bag is big enough that even when the person jumps all the way up, the bag still touches the scale.)

Wouldn't the scale register a higher reading as the person was pushing down on it, and then not register the weight of the person at all while the person was accelerating upward -- just the same as if you were to jump on a bathroom scale without a plastic baggie?

Does this have anything to do with a birdie in a cage?

-SB