The setup for this experiment would be a bus on a weighbridge and a number of people on that bus jumping up at the same time. Does the weighbridge still indicate the same mass and does this have to do with the air displacement that does or does not take place?
Answer
Gerrit,
Suppose that in the beginning the bus with people weighs M kg. The moment everyone rejects to jump up, you will read more than M kg on the scale. If everyone can jump high enough or hang in the air long enough (without touching the bus), you would find (after the stabilization of the whole) that you read less than M kg. But that is precisely the difficult and direct explanation: in such a way air does not have enough carrying capacity at all to keep people in the air. In other words, the air is not “firm” enough to act as a support between people and the bus.
If you were to do the same experiment with a jar of water, pushing off from the bottom, the weight would remain the same. After all, water has sufficient carrying capacity. You would see the same effect if you took a hollow cylinder instead of a canister, and not the people but a disk that is just a little narrower than the inner diameter of the cylinder. Because in such a case the air can only slowly escape from below the disc to above the disc, the lower air will be compressed and transfer the weight of the disc to the cylinder.
Answered by
ir. Bart De Schouwer
For my position I am the manager of a group of engineers who maintain production equipment. It is mainly with my ready knowledge (education, interests, …) that I could answer questions.
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http://www.imec-int.com
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