Episode #125 of the Stack Overflow podcast is here. We talk Tilde Club and mechanical keyboards. Listen now

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There is kind of standard trick to solve this problem. When you apply some force $F$ to a body for a period of time $t$ the momentum of this body will change by $F*t$. Let's say we have a fire horse which produces a water stream. 1500 liters per minute, speed is 20 m/s. (I am not sure these are specifications of some real fire fighting truck). So, each ...

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Use a valve on the inflow tube similar to the one in your toilet tank: a float on the end of a lever turns the flow off when it reaches the desired level.

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If you heat a sphere of water from the center in the absence of gravity, I see no reason for convective instability (in the usual sense of buoyancy of hot fluid). The heat transport should purely conductive, and the idealized heat conduction equation could be solved by the familiar Green function method. Hot liquid expands, so the sphere will inevitably ...

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In absence of gravity water start to evaporate due to kinetic motion of water molecules.The making of water vapor absorbing latent heat from either near heat source or from water itself .So in this way water become solid ice which was locate far from heat source and other part become water vapor.

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The heat flow will be radial. A bubble will form at the center of the sphere and increase in volume with time. Because of the much greater specific volume of the vapor compared to the liquid, the vapor will push the surrounding fluid outward radially, just as if a non-condensible gas were being released at the center of the sphere. So, within the ...

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The surface tension only affects the pressure inside the liquid if the surface is curved: $$P_{\rm inside}= P_{\rm outside}+ 2\sigma/R,$$ where $\sigma$ is the surface tension and $R$ the radius of curvature. It is important in the formation of bubbles during the boiling process as $R$ is very small when the bubble forms. This is why boiling tends to ...

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As you point out, if expansion of the water is prevented then the water cannot proceed through the phase transition. It itself that is not a problem; there is the phenomenon of supercooled water. The state of supercooled water is that the temperature of the water is below its freezing point, but it hasn't crystalyzed. To some extent the crystalization needs ...

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It happens because the kinetics of boiling have a finite time scale. This is because to begin boiling, a nucleus must be furnished to trigger the phase change. That nucleus usually takes the form of an air bubble in a crack or crevice in the water container's walls. If the bubble exists when the boiling point is reached, boiling begins without delay. If no ...

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I see this effect on my electric stovetop. The bottoms of my pots are no longer quite flat, and pushing downward on the pot improves the thermal contact between the pot and the heating element. The effect is present whether I push down on the bottom of the pot with a ladle, or whether I push down on the handles on the outside of the pot. On a gas stovetop,...

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Throwing water 100 meters in 1 second means the water has to have a speed of 100m/s. So the question becomes "how much pressure do I need to achieve those speeds?" What you're looking for is Bernoulli equation. They state that for any given incompressible flow (such as water out of a nozzle): $$\frac{v^2}{2}+gz+\frac{p}{\rho}=C$$ In this equation $v$ is ...

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Ice VII occurs above 3 GPa. Pressure at depth $z$ is $p =\rho g z$, so the critical depth for $\rho=1050$ kg/m$^3$ is $z=290,951.4$ m. So we need a 291 km deep ocean to get high pressure ice. Not very likely on Earth.

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The reason that lightning strikes a lightning rod rather than another point is that the lightning rod provides a path of least resistance from it to the ground. This is the reason for the 25 Ω limit in the regulations. However, if you want to use electricity to heat something up, you need have a high enough resistance in the path of the electricity to ...

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Lightning can boil water. The reason why many objects explode when struck is that the water they contain vaporises. So there is enough energy available. However, lightning is a very transient phenomenon, so the amount of water you could manage to bring to boiling point, without wasting heat on steam explosions, would be dependent on passing the heat energy ...

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The real question here is "how much water"? But let's start with the literal question. Heating water to the boiling point (373K) just means that the lightning current heats up a resistor in the path to 373K. That means the resistor shouldn't melt at those temperatures. Is that physically possible? Sure - plenty of metals will melt at much higher ...

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I must say,the way mythbusters handled this myth bugs me intensely. Yes it's true it wont work the way it was shown in the movie, but it definitely can be done. Just weight the upturned boat until it has a slight positive buoyancy.Then it's easy for the guys to hold it down. Job Done

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