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Q & A: effect of gravity on pressure

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Most recent answer: 10/09/2012
Q:
Can there be different pressures within a closed system? Specifically, in a syringe with 3 mls of medication in it at rest, is the pressure the same all throughout or is the pressure (ever so slightly) higher at the bottom? It seems to me the pressure would be higher because the weight (mass?) of the fluid is acting on it. I understand with Pascal's principle, if an outside source of pressure were applied it would be evenly distributed throughout the system, but if no outside force is acting on the system does it still have the same pressure throughout?
- Verity (age 35)
Salt Lake City, UT
A:
You're absolutely right that gravity causes a small difference between the pressures at the top and bottom of the syringe. If the fluid in it is water and the height is say 3 cm then the pressure difference is about 0.003 atmospheres. That's small but measurable.

Mike W.

(published on 10/09/2012)

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