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I am working on an engineering problem, but need some physics thinking to get my head around it.

I have a DC pump connected to one end of a slim tube. The other end of the tube is connected to a large airbag, which someone is sitting on.

Initially, the airbag is empty and the pump is switched off. I then switch the pump on and allow it to fill the airbag until the person sitting on it has been completely lifted from the floor.

This sounds simple enough to visualise. The trouble I am having is calculating the pressure that the pump 'sees' once the person has been lifted from the floor. I initially went for the force/area of contact calculation, but that only gives the pressure on the backside of the person.

What I want to know is how the weight of the person affects the pressure in the airbag as well as the pressure at the nozzle.

Any and all input will be greatly appreciated.

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Having the bag in equilibrium, with no air intake or loss, and with the individual frozen and being fully supported by the bag, then the force/area of contact (on the floor) calculation gives the air pressure inside the air bag, tubing and pump discharge port. The key is to stop air flow from the pump into the bag (say, by closing a valve) once the individual lifts off, and before the bag goes off.... An analogy would be the tire pressure: it has a range that will fully support the weight on the tire, being inversely proportional to the tire's foot print.

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