Mike Dunlavey
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 1d comment Pressure required for gas to flow through an orifice There is no non-zero pressure where the flow will be zero. You have a case of flow through an orifice. 2d comment What causes the buzzing sound when the electricity changes into heat? @HonzaZidek: DC would be silent, except for maybe a "click" when turning on or off. It isn't that the vibration of the electrons mechanically couples to the metal. The magnetic field vibrates, and that couples to the metal by inducing currents in it (in addition to magnetic attraction). May 3 comment Intuitive explanation for lower pressure above airfoil When you say "Bernoulli does not explain wing lift" are you by any chance confusing Bernoulli with the "equal transit time fallacy"? The Bernoulli principle isn't wrong - what's wrong is the way it is typically used to explain wing lift, assuming air parcels are re-united at the trailing edge. I've found this to be the clearest explanation. May 3 comment Intuitive explanation for lower pressure above airfoil @MrYouMath: I'm not sure, but I think you're onto something. May 2 comment Intuitive explanation for lower pressure above airfoil @MrYouMath: I agree with this explanation, but I would put it in simpler terms. It's just a consequence of $F=ma$. There is a velocity difference if and only if there is a pressure difference. One implies the other. As far as incompressibility is concerned, all that means is we're dealing with speeds well below the speed of sound. It does not mean the fluid is stiff. Apr 29 comment Physical explanation of Pascal’s Law Google "lever". Apr 28 comment How can I understand $\mathrm ds^2 = -c\,\mathrm dt^2 + [\mathrm dx-v_s(t)f(r_s)\mathrm dt]^2 +\mathrm dy^2 +\mathrm dz^2$ in the simplest way? @Nihal: Why not start now? It's fun. Apr 28 comment How can I understand $\mathrm ds^2 = -c\,\mathrm dt^2 + [\mathrm dx-v_s(t)f(r_s)\mathrm dt]^2 +\mathrm dy^2 +\mathrm dz^2$ in the simplest way? @Nihal: Yes, but not difficult. $d something$ just means "an amount of something that is small enough that you don't have to worry about curviness". Like suppose you have two points on a curvy line close together but not the same point. If the horizontal distance between them is $dx$ and the vertical distance is $dy$, what is the distance on the line between them, $ds$? It's just the square root of the other two distances squared and added together, right? Apr 27 comment Centripetal force: if radius decreases, does ANGULAR or TANGENTIAL velocity change? @Al: I doubt your first point. On the second point, I've been wondering that myself. I'm supposing some kind of infinitessimal argument would clear it up, but I haven't been able to give it enough thought. Apr 21 comment What amount of force could be created by a person “swimming” in air? Two points: 1) birds do it. You're not much of a bird, but the idea should still work. 2) Force is not just momentum, it is momentum per time. Apr 20 comment flow rate measurement of a fluid It's just a wedge. It travels in a circle, but it's still a wedge. Apr 18 comment Does physics claim that every possible world has or will exist? @user3293056: These interpretations can be useful. When I dabbled in quantum computation some years ago,the many-worlds interpretation was a really nice way to think about what was going on. Apr 16 comment When does the shock occurred? 3-when the speed of the local flow over the airfoil exceeds Mach 1. This first occurs on the upper surface of the airfoil when the speed of the aircraft is still less than Mach 1. Apr 12 comment Why do water waves with longer wavelengths travel faster? @veronika: I think you might have it backward. For sailboats with displacement hulls, the length of the waterline determines the wavelength of the wave it generates, and that affects the maximum speed the boat can go. Apr 9 comment Plane landing into a tunnel If you could see the air around an airplane, like if it flies through smoke, you would see that the weight of the airplane causes the air to be pushed/sucked downward. This forms two large rotary circulation patterns, one from the end of each wing. This persists behind the airplane in the form of a wake, just like a speedboat. Nothing about flying in a tunnel prevents this. Of course, if there is a second plane flying behind the first, the wake is a problem to be avoided, but that's true, tunnel or not. Apr 8 comment If a hole is drilled at the bottom of a vessel, why is the pressure of the liquid leaving the vessel equal to atmospheric pressure? The fluid is accelerated as it leaves the hole. The only thing that can accelerate a fluid is a difference in pressure. Inside the tank, there is pressure due to the height of fluid above the hole (+ atmospheric pressure). Outside the tank, the pressure is just atmospheric. That is a pressure difference. It makes the fluid accelerate. Whenever fluid accelerates, you will find a pressure difference. (That's Bernoulli, by the way.) Apr 7 comment In a flowing fluid, why the particles are gathering together under critic distance and separating above this distance? It is good that you have the courage to ask a question in English, not your native language. However, I just don't understand the question. Maybe you can revise it? Mar 24 comment Torricelli's speed of efflux law @Schrodinger: It is talking about velocity at the port, not some distance away. Of course if the flow is vertical it will gain kinetic energy proportional to how far it has fallen from the port, but then it is no longer in the port. Mar 23 comment Light scattering - creating an atmosphere that a laser will be visible in Dust or flour, and a fan. Mar 21 comment Bernoulli principle and viscous loss Why does the flow remain the same? R will convert the kinetic energy to heat, slowing down the fluid until it effectively stops. The fluid will feel this slowing force as a pressure drop across the resistor.