# Tag Info

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Well - air does have "relative humidity" and this really affects the things that interact with it. For example - you will have a hard time cooling down by sweating when the relative humidity is very high, as the rate of evaporation that you can achieve (and therefore heat rejection) becomes quite low: this is why you end up "sweaty" on a hot muggy day. ...

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breathing: Since the tyre is a about 2 atm at the surface, at 50m it will have a pressure of 6 atm if the tyre is thin (membrane) or less if is "partially rigid" (down to 2 atm if the tyre is totally rigid). If it behaves like a membrane, air will come out if you push the valve (with the tongue, I guess it would require practising a lot :D) because the ...

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The pressure at 50 m is about 6 atm. Since the pressure in the tyre has a pressure of about 2 atm, there are 2 possibilities when the valve is opened. The tyre (which has been compressed by the water pressure) is rigid enough to return to it's previous shape and water enters the tyre (very likely). Or the air stays in the tyre and the water stays out. The ...

3

If you neglect viscosity, Bernoulli's equation (just Navier-Stokes without frictional or stress terms) will get you into the ballpark: $$P_g + \frac{1}{2}\rho_g v_g^2 = P_a$$ Where the $g$ subscripts pertain to the gas and the $a$ subscript to the ambient. The gas density $\rho_g \equiv M / V$ is the ratio of the mass of gas (M) in the tank to the volume ...

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If wanted to pump water then it would be better to "push" and not "pull", since otherwise the pressure in the pump could drop to low such that cavitation could occur. But you are dealing with "pumping" a gas this will not be a problem. The an effect which could alter the performance would be the angle of attack of the blades of the fan. If the fan would be ...

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The simple answer to "why is the pressure inside a soap bubble higher than outside," is that a higher pressure than the local atmosphere is required to make the bubble in the first place! This requirement comes from the need to counterbalance the surface tension force. For stable conditions, $$F_i = F_o + F_s$$ Where $F_i$ is the force due to inside ...

3

Without repeating the mathematics of @alemi's answer, let's just think about one other thing: Buoyancy is a function of depth - that is, as you descend your lungs are compressed and your buoyancy decreases, then goes negative (depending on the fat content of your body - if you have enough fat, you remain positively buoyant at any depth since you do not need ...

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I like Jerry Schirmer's answer, but I was worried that instead of modelling you swimming as fast as you can as a constant force, I thought it would be interesting to consider swimming as fast as you can as a constant power. This seems more logical to me as if you are really trying to go as fast as you can, you will be limited by how hard you work, how fast ...

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OK, lets solve this in as simple an approximation as possible. I"m going to assume that the whole trip happens at the appropriate terminal velocity, and that acceleration times are very small. Furthermore, I"m going to model the resistant force${}^{1}$ of the water as $F = cv^{2}$, for some constant $c$. On the way down, you have the the resistant force ...

5

According to the RSB: Migrating (European) swallows cover 200 miles a day, mainly during daylight, at speeds of 17-22 miles per hour. The maximum flight speed is 35 mph I think that calculating the flight speed of a bird from first principles would be impossibly difficult as there are just too many variables. The web site you link does get an answer ...

2

Working out how much force is required to move through a fluid, whether it's air or water, is surprisingly difficult because there are two effects you need to take into account. However neither of those effects is pressure (or at least only indirectly related to pressure). The first effect is viscosity, which is simply how thick the fluid is. Obviously it's ...

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The air in lungs, ears, stomach and intestine has the same pressure as the air pressure outside the human body, ensures that you don't get crushed by the air pressure. If you have already managed living almost compensating the air pressure on you, moving in that air is simple.

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I'll use this answer to provide some information that's mostly orthogonal to what Phonon said. As Phonon pointed out, the speed of sound depends on temperature, not pressure. It's cold on the top of high mountains, so the speed of sound would tend to be lower. Some mechanisms for sound production have a frequency that depends on the speed of sound, and ...

3

There more sides to this scenario that you're considering. Firstly, if we are assuming that the temperature is the same at sea level and on the high mountains, then the speed of sound doesn't actually change, as a constant temperature will take care of the air pressure-density ratio. $$c = \sqrt{\kappa \frac{p}{\rho}}$$ Where $p$: static air pressure, ...

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