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82

Air molecules $(\require{mhchem}\ce{N2_}$ and $\ce{O_2})$ have an average velocity of around $500\text{ m/s}$, varying some depending on the temperature. This means that a nice $5\text{ m/s}$ wind is a hundred times slower, and the energy represented by wind is 10,000 times smaller than the thermal energy. Therefore, wind does not have considerably more ...


54

The reason is because the heat loss occurs mostly in the windows and the fenestration. The idea is that you would like the incoming air to be heated up. Also, it creates an air curtain that prevents more heat from being lost through this exposed areas. The final reason is to make the temperature of the room more or less uniform. If the heaters were placed at ...


50

Ice cubes have three distinct cooling effects: The cube, initially at sub-zero temperature, absorbs some heat to reach fusion point (0⁰C). The cube absorbs more heat to switch phase: it takes some energy to turn 1 kg of ice at 0⁰C into 1 kg of liquid water at 0⁰C. The water absorbs some heat to become warmer than 0⁰C. The three effects occur more or less ...


48

Partly practical, the wall under the windows isn't useful for anything else. We had a house where the heaters were placed in the middle of the only empty walls, so nowhere you could put furniture, bookcases, etc. Before double glazing there would be a draft from the windows so the idea was to heat this incoming air by having a radiator immediately below the ...


47

You blow away the flame from its fuel source. If you would blow less hard the flame might burn harder because more air is supplied to the flame (similar to a Bunsen burner). Because normally the flame of a candle gets its oxygen through a convectional airflow generated by the heat of the flame. The reason why the flame is blown away from the candle is ...


43

No. Boiling doesn't mean that the water will cook anything. If you have boiling water at 30°C you could touch it (if we forget that it's at really low pressure) and nothing would happen. Boiling is not what cooks, but temperature. In fact, if you want to purify water at high altitudes, you need to boil water more time because it will be at lower ...


39

Since this is a physics forum I assume the OP is interested in a quantitative answer in terms of the efficiency of the system and how it differs based on the relative positioning of heat sources and heat sinks. The math required to analyzed such a system is too much for me to manage right now, but I believe the following principles apply and are objectively ...


37

This is a very good question. Einstein himself, in a 1907 review (available in translation as Am. J. Phys. 45, 512 (1977), e.g. here), and Planck, one year later, assumed the first and second law of thermodynamics to be covariant, and derived from that the following transformation rule for the temperature: $$ T' = T/\gamma, \quad \gamma = ...


22

We want to show that "infinitesimal" changes in heat along a given path in thermodynamic state space can be modeled via a differential 1-form conventionally called $\delta Q$. The strategy. We introduce a certain kind mathematical object called a cochain. We argue that in thermodynamics, heat can naturally be modeled by a cochain. We note a mathematical ...


21

Actually, temperature is defined as $$\frac{1}{T} = \frac{\partial S}{\partial E} = \frac{k_B}{\Omega}\frac{\partial\Omega}{\partial E}$$ So in order to have zero temperature, you would need a system with either zero multiplicity, which you can't have by definition, or an infinite derivative $\partial\Omega/\partial E$ even though the multiplicity itself ...


19

Combustion is a gas phase reaction. There are two requirements to generate a stable flame. Firstly the temperature must be high enough to vapourise the combustible material (wax in this case), and secondly the temperature must be high enough to generate the activation energy needed for the reaction. Heat is needed because gas phase molecules of wax and ...


19

It's not poop. It's fly barf. A fly spends about 25% of its time re-digesting and it only can eat liquids. It mixes the eaten food with the appropriate enzyme for digestion. The fly does this by retrieving the eaten food from its digestive system (a vomit of sorts), and drop by drop it is placed on the surface on which the fly is sitting. Only then is it ...


18

Ahem, I come to you from Seasoned Advice (cooking). As Beta suggested, questions like this one would not be uncommon there. The agitation of boiling water has nothing to do with cooking pasta except in that it helps keep the pasta from sticking. Whether it makes good pasta to hydrate it without heat (or at least a lot of heat) is a source of some debate, ...


17

From a purely temperature point of view, not human perceived level of hotness, it is better to point the fan outward. This is because the fan motor will dissipate some heat, and when the air is blown outwards, this heat goes outside. This is all assuming the room has enough ventillation cracks and the like that the pressure inside is still effectively the ...


17

There are ways to define "temperatures" for single molecules or atoms, but they are subtly different than the way in which temperature is defined for bulk material. Temperature is essentially a statistical quantity as averaged over the various internal states of the material, and for large composite systems at equilibrium, the internal energy levels are ...


17

As a supplement to @tpg2114's answer, it also depends on the "wetness" of an object. As most people should know the evaporation of water requires energy and this lowers the temperature. The lowest temperature a wet object can reach is what is called the "wet-bulb temperature." This can be several degrees lower than the "dry-bulb temperature," the amount ...


17

If the particles are not point-like, they will take up some volume. As the gas is compressed, the collision frequency will rise more quickly, which will make the pressure-volume curve change. The corrections in the Van der Waals model of a real gas accounts for the volume of the particles. Also if they have internal structure, that structure can have ...


16

Your statement is somewhat subjective, so really can only be answered by trying to put together what thoughts about physics such great physicists were thinking when they made their statements. Firstly, the laws of thermodynamics have very different origins and putative theoretical justifications and indeed the Eddington quote only talks about the second. I ...


15

Lets take each case and make some calculation. So, the first case, waiting for 5 minutes than adding some cold water. Assume the following values: The initial "hot" temperature of the coffee $T_H=80^{\circ}C$ The temperature of the surrounding medium $T_m=23^{\circ}C$ Using Newtons cooling law $$\frac{dT}{dt}=-k(T-T_m)$$ and after a simple integration ...


15

The other answers address your question quite well. Just as a reminder of the ability to be burned by a strong enough wind, the image below shows the Chelyabinsk meteor during entry into Earth's atmosphere last year over Russia. :)


15

It can't be from the moisture in the air. If there was enough moisture in the air to produce condensation then it would be condensing on everything. There would actually be less of it condensing on the tailpipe, because the tailpipe is quite warm. In fact the water is generated by the combustion of the fuel in the car. It comes from the hydrogen in the ...


14

Typically freezing rain falls as water because the air is warm enough that it won't be ice, but then it freezes when it's on the surface of things because those surfaces are below freezing. This usually happens with roads and the ground when it's been a long time of very cold temperatures. Bridges also tend to get colder, faster, than other roads because ...


13

A convenient operational definition of temperature is that it is a measure of the average translational kinetic energy associated with the disordered microscopic motion of atoms and molecules. The underlying framework of all matter is quantum mechanical. This means that the Heisenberg Uncertainty principle holds. Even for a single particle the HUP ...


13

"Total energy of the Earth" is somewhat of an odd concept, but there's no reason we can't really entertain it. It brings up some genuinely difficult questions. The right way to approach this is to define the system correctly and then identify forms of energy content and flows. Things to "count" in the Earth's energy: Heat content Nuclear energy ...


12

Well, I can share with you one experience from my high school. I wanted to boil coffee in my caffetier without a cooker. We had the vacuum pump in the physics room so there was the way to "boil" the water without getting it in 100°C. I did it... and coffee tasted horrible. Never try it again.


11

A fundamental principle of thermodynamics is that heat flows from warm places to cold ones, through either convection, conduction or radiation, and it will continue to do so until the temperature equalizes across the system. The stones are colder than the whiskey when you put them in the glass, so as the system heads towards equilibrium, the whiskey gets ...


11

It's because the Kelvin scale was and still is defined so that as a measure of temperature difference, one kelvin exactly coincides with one Celsius degree. So the temperature in kelvins was defined as the temperature in Celsius degrees minus $A$ where $A=273.15$ °C is the temperature of the absolute zero, without any additional multiplicative factor. When ...


11

As a computer scientist who deeply respects the beautiful and astonishing relativistic and quantum frameworks that emerged about a century ago, I would only like to note that I strongly agree that thermodynamics defines the deepest levels of reality. Why? First you must understand what information is, since entropic definitions by themselves only tell you ...


10

Legendre transformations are commonly used in thermodynamics (to switch between different independent variables) and classical mechanics (to switch between the Lagrange and Hamilton formalisms). But you rightly ask: what exactly is a Legendre transformation? Where does it come from? What makes it work? In (1D) classical mechanics, for example: if we have a ...


10

TL;DR: Whiskey stones work by absorbing heat from the whiskey in an attempt to reach thermal equilibrium1. As Thomas mentioned, ice has three cooling effects: Ice itself takes 2.11 kilojoules of heat per g to have its temperature increased by 1 degree (Celsius). This number is known as "specific heat capacity" Ice takes 334 kilojoules of heat per kg at 0 ...



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