# Tag Info

7

You can absolutely have negative pressure in solids or liquids. Think of an elastic solid being forced to expand to to adhesion to the walls of some chamber. That has negative pressure even if the comparison is a total vacuum. Depending on the bulk modulus of the material being stretched and the strength of the interaction with the walls of the chamber ...

4

Creating a vacuum above carbonated drinks causes the CO2 to outgas faster--simply because there is no CO2 above the drink to diffuse back into the liquid. In physical terms this means there is no vapor pressure of CO2 above the liquid, so net movement of CO2 is from the drink to the space above it. If you leave a closed carbonated drink bottle long enough, ...

4

You're right, absolute pressure can't be negative. Of course, you can easily have a $20\: \mathrm{PSI}$ pressure differential (although not without pressure above $1\: \mathrm{ATM}$ since that's $14.22\: \mathrm{PSI}$ at sea level). Check out Wikipedia on the zero-reference: Absolute pressure is zero-referenced against a perfect vacuum, so it is ...

3

The question is asking what is the force exerted by the water on either of the two faces of the plate. The net force will be zero as force on either side sides cancel, so your intuition made sense. The force on a side comes from water pressure across the triangular surface. The pressure at any point on the triangle depends on the depth of that point. ...

2

Air escapes via multiple mechanisms. Diffusion through the material: Most materials have some permeability to air. Air molecules can fit between the rubber molecules. The N2 and O2 molecules are so few and far between that they don't interact. The average force on a molecule is zero as it randomly walks through the rubber, but the concentration difference ...

1

The simple answer is that a wing moves through the air generally at a non-zero angle of attack. The air flow below the wing sort of impacts the wing surface, compressing and slowing down as it is deflected. See this Drawing:

1

Actually, the reason is anthropic! The original unit for sound intensity is the bel, named after Alexander Graham Bell. But the bel is "inconveniently large" for most purposes1, so we use the decibel (literally 1/10 of the bel or 10 dB = 1B), hence the factor 10. Ordinary conversation is $\sim$65 dB, this would be 6.5 B

1

It took me quite some time to clearly understand the experiment you're describing. Actually, pouring a full bottle in a container is a quite intriguing thing. Consider the following starting configuration : This of course is an unstable situation, as the pressure $P_0$ cannot be at the same time the pressure of the air in the bottle, and the atmospheric ...

1

To make a less apetizing point: The argument leading to the water levels being equal starts from an ideal fluid. Now a sewer backing up is far from ideal. I would expect solid pieces like toilet paper and feces clogging the pipe leading up to the shower (especially if the shower drain has a siphon), while the toilet drain is made for larger pieces fitting ...

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