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You partially fill an L-shaped tube with water and completely seal it as shown (so that there is a small pocket of air remaining on the right side). What happens to the pressure at the bottom of the tube when you rotate it 360 degrees and allow the pocket of air to bubble up to the top left?
You partially fill an L-shaped tube with water and completely seal it as shown (so that there is a small pocket of air remaining on the right side). What happens to the pressure at the bottom of the tube when you rotate it 360 degrees and allow the pocket of air to bubble up to the top left?
A) It increases.
B) It remains the same.
C) It decreases.
D) It cannot be determined.
A) It increases.
B) It remains the same.
C) It decreases.
D) It cannot be determined.
Solution: The pressure increases.
Solution: The pressure increases.
The volume of the water remains the same as it is (mostly) incompressible. So the volume of the air remains the same in the enclosed container. The number of moles of air remain the same as there is no escape mechanism. The temperature of air remains the same as there is no mechanism for it to change (no compression, expansion, heating, or cooling). So the pressure in the air remains the same by the ideal gas law. The bottom of the tube is now a greater distance (d) below the reference point of the air-water interface (with an unchanged pressure, P0). So the pressure in the static fluid increases according to the formula P = P0 + ρgd. See this video for experimental evidence (but please ignore the wrong explanation).
The volume of the water remains the same as it is (mostly) incompressible. So the volume of the air remains the same in the enclosed container. The number of moles of air remain the same as there is no escape mechanism. The temperature of air remains the same as there is no mechanism for it to change (no compression, expansion, heating, or cooling). So the pressure in the air remains the same by the ideal gas law. The bottom of the tube is now a greater distance (d) below the reference point of the air-water interface (with an unchanged pressure, P0). So the pressure in the static fluid increases according to the formula P = P0 + ρgd. See this video for experimental evidence (but please ignore the wrong explanation).
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