Imagine a lorry, filled with birds. If a sealed truckload of birds is transported onto a scales, and the birds are prompted to fly up at once – and no longer touch the floor – the weight would remain the same if the lorry. The volume and air pressure of accounted for the birds still remains in the sealed system.
So the load’s weight of the truck is not the weight of the load touching the floor but it is weight the mass in the sealed space.
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