# Tag Info

28

The metal mug will equilibrate with the water much faster than the foam mug will— but after that the heat has no place to go except to be lost as steam via natural convection or transferred away through radiation,$^\dagger$ heat transfer mechanisms which do not depend on the material of the mug. It turns out that radiation plays a very small role as shown ...

15

I would suggest that the bottom penny does not have the same composition. A zinc penny is mentioned in the comments (BTW, what a tedious video) and zinc has a much lower melting point than copper (420 C vs 1085C). Copper plated zinc pennies were introduced in 1982. Given that it started to melt almost straight away, I think that is your answer. At about 10 ...

14

There's two possibilities that are immediately obvious. The first is that the pressure inside the house is slightly lower than the pressure outside the house before you light the fireplace. This would cause air to flow down the chimney into the house which would keep push the flame into the house instead of up the chimney. This would be easily testable if ...

12

You're not getting enough Make-Up Air. I strongly encourage you to install a CO detector in you home and reassess your HVAC situation (especially the 'V' part, ventilation). Lack of sufficient makeup-air in a house with gas fired equipment is dangerous. This is usually more of a problem with new-construction homes that are built to be nearly hermetic. ...

11

Quite simply, no. Water memory doesn't appear to violate any physical laws, and the claims made about it are not well-defined or specific enough to be falsified (e.g. with an entropic argument). It's revealing that while a scientist could be convinced that he's wrong, there's nothing that could change the mind of a homeopath. The best we can do is test the ...

10

The heat loss from an open cup was probably dominated by evaporation so the material didn't have very much effect and was within the limits of your experiment.

7

The cup that insulates the best will minimize convention and present the hottest liquid at the surface, where the delta T between liquid and air will determine cooling. The cup that conducts heat the best will carry heat from the top to the bottom and cause convection currents. The heat will spread more evenly throughout the liquid and the surface liquid ...

7

If you drop an egg then it looks as though the process is irreversible and that the information about the original state of the egg is lost. However this isn't the case. The equations describing how the egg shatters are all time reversible so in principle, if not in practice, we could take the shattered egg and evolve time backwards to reconstruct it. ...

6

According to this lecture from the University of Edinburgh, numerical simulations of N-body systems suggest a half-mass relaxation time: $$t_\text{rh} = 0.138\frac{N^{1/2}r_\text{h}^{3/2}}{m^{1/2}G^{1/2}\ln(\gamma N)}$$ where $r_\text{h}$ is the radius that initially contains half the mass of the system, $G$ is the gravitational constant, $m$ is the ...

6

Unless I'm missing something here, you can speed up reaching the equilibrium temperature simply by stirring the water mixture. Better still, pour in the cold water from a height so it produces turbulent currents as the hot and cold water mix.

6

It's only "sticky" when you stick it to something that was initially warmer than freezing. Let's say you stick your finger against a (very cold) ice cube. Two things happen in sequence: The heat from your finger transfers into the ice and melts it slightly, forming a thin water layer. The heat dissipates further into the cube, and the water refreezes. ...

6

The notion of temperature is all about how the equilibrium an otherwise isolated system shifts when the system's internal energy changes. So you do not need to worry about whether this internal energy is kinetic, potential, whatever. Actually the temperature is not quite the ensemble average kinetic energy. Your statement is true for an ideal gas and also ...

5

I will not be able to feel the heat form the fire as a result of convection as there is no atmosphere True, but no atmosphere also means no oxygen for the fire, so this example is kind'a off. Now my question is will I be able to feel the heat from the fire as a result of radiation? Yes. If the fire was at Earth (in an atmosphere with oxygen) the ...

5

I'm not too qualified to speak about the Black Hole Information Paradox, but I think I can say a thing or two about Maxwell Daemons. I think the essential "flaw" in your description is the assumption that Maxwell Daemons destroy information. The do not, and I describe what they actually do in my answer to the Physics SE Question "How can the microstates be ...

5

There is no such thing as cold radiation. In the examples you link above, the issue is that the walls of the incubator are colder than the air or the baby. What actually happens in this situation is this: all objects radiate with a certain intensity which is based on their temperature (among other things). A baby in an incubator is constantly radiating ...

4

If I recall it correctly, the information sunk into black hole can be considered encoded in the ripples on black hole surface, much like egg impact parameters which could in principle be deciphered (at least partially; even quantum theories give us certain confidence intervals) from shattered egg fragments. Falling objects will necessarily have mass, and ...

4

It's internal reflection in the camera. It's an inverted image of the actual exploding material.

4

It's really complex, and the answer from Shep is a bit imprecise. Ice at temperatures just below freezing has the remarkable property of not being frozen on the surface. There is a extremely thin layer of liquid water on the surface. How thin? 70 nm at 272 K, but only 10 nm at 262 K. This water layer can act as a lubricant, but with less lubricant the ...

4

You need a "draft". When you light the fireplace, initially the heated combustion products want to rise directly up the chimney, but after that occurs for a few seconds it results in a partial vacuum in the house, attempting to suck air back down the chimney. This cause the fire to be blown/pulled outwards into the room. (With a conventional wood-burning ...

3

Think of a pressure cooker... The higher the pressure, the higher the boiling temperature. You need a vessel that will hold the pressure at 350C. Wikipedia gives a formula for the pressure need to get the boiling temperature of water up to a certain value. The formula is $$T_b=1730.53/(8.07131-\log_{10}P) -233.426$$ where $T_b$ is the boiling temperature ...

3

Assume the bread is consisted of similar tiny tiny pieces, each having the same mass and surface. Also, assume there is a uniform heat flux everywhere. The pieces close to a hole or at the sides of the bread have a larger portion of their surface exposed to heat, than a piece that is surrounded by other pieces, therefore they absorb heat at a faster rate. ...

3

You asked for intuitive sense and I'll try to provide it. The formula is: $$\Delta S = \frac{\Delta Q}{T}$$ So, you can have $\Delta S_1=\frac{\Delta Q}{T_{lower}}$ and $\Delta S_2=\frac{\Delta Q}{T_{higher}}$ Assume the $\Delta Q$ is the same in each case. The denominator controls the "largeness" of the $\Delta S$. Therefore, $\Delta S_1 > \Delta ... 3 Lets start with some assumptions. You probably have the beam from a laser pointer in mind so the hole size you want to burn is about$4\,\text{mm}$in diameter. Lets assume that it's roughly$-5^\circ\text{C}$($23^\circ\text{F}$) outside. One final assumption, and this one is just a guesstimate, lets assume that due to thermal conductivity you need to ... 3 Object don't posses heat. They posses internal energy. Heat, like work, is a transfer of energy and is a property of a process or interaction not of an object. 3 There seems to be a slightly lowered pressure inside the room the fireplace is in, which leads to air actually streaming down the chimney to equalize it, and this blows the flames into the room. When you open the door, you allow air draught to stream into the room and up the chimney, as it is supposed to, and that sucks the flames into the chimney. ... 3 Generations of physics students, including me, have got mixed up about the sign of work done. That's because the phrase work done can mean work done on the gas or work done by the gas, and these are equal but with opposite signs. I don't think there is any perfect way to deal with this except by using your common sense. If an expanding gas does work then ... 3 I'll answer your second question first, because then your first one is easier. In short, yes, the equilibration of temperature between two bodies is absolutely universal - it doesn't depend on how the heat is transferred, and in particular it does apply to radiative transfer. And, indeed, once two bodies have reached thermal equilibrium through radiative ... 3 Even if light from stars cannot enter the box, eventually the box and the surrounding space will come to thermodynamic equilibrium and the box will emit blackbody (or, more likely, graybody) radiation both inside and out and the equilibrium temperature attained. If you take the box far from any starlight there is still the sea of photons that make up the ... 3 That is nothing but a mechanical relation valid for every type of isotropic fluid (even viscous, in the quasi-static regime), so gases in particular, no matter any further state equation. 3 As you said, the relation you have is $$dE = TdS + FdL$$ So one maxwell relation is $$\left(\frac{\partial T}{\partial L}\right)_S = \left(\frac{\partial F}{\partial S}\right)_L$$ Which is the one you have obtained. For get the other do the following transformation $$dE = TdS + FdL = d(ST) - SdT + FdL$$ $$\implies d(E-ST) = -SdT + FdL$$ Since$-SdT + ...

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