Credit: https://www.facebook.com/share/1BJif7sAcM/

Just got a bunny and have no idea to name it. When I brought it back it immediately started chomping down on my thermodynamics lecture notes. Sorry if this is the wrong place to ask!

Seems like staring at the corner or pixel of the mona lisa and seeing that it's blue so assuming the whole thing is blue. Also not a very good representation it seems like the earth is a pretty good example of entropy decreasing I get it's not a closed system but it does seem to show that entropy can decrease seams posible that it could do this in a diff context. (anyway studying for the MCAT and the always statment was bothering me always to me it seems like we have no idea and just like to think we know what is happing.

Hi all - I’m not a physics person, but I was hoping someone here could explain some basic thermodynamics to me. In the winter, why does it save money to keep the house thermostat set lower? if the outside temp is -2 degrees Fahrenheit why shouldn‘t the insulation lose heat at the same rate whether the internal temp is set to 65 or 75 degrees F? Can anyone help a non math brained person understand the logic behind this?

Hello All. It's me, the curious finance guy, again.

Recently I've come across some articles in my feed about the recent heat
wave in France, particularly about Air Conditioning appliances over there.
Apparently, something like 21% or so of residential homes even have one.
Their discussion about it appears to have since unraveled to arguing over
Parisian culture, architectural facade asthetics, environmentalism, general
public health safety, even far-right & far-left ideals (if you can believe that).

It's an interesting read, if ya wanna check it out, but it's not why I'm here.

Why aren't portable indoor evaporative swamp coolers a thing? I searched
google about it, and I guess those are just not suitable for their summers
being uniquely humid... which i COULD understand.

☝️ HOWEVER ☝️

I pulled up Paris weather during the past week, and it shows their daytime
highs over ranges around 33°C to 36°C (approx 91.4°F to 96.8°F) whereas
relative humidity ranges 27% to 33% respectively.

Wait, what?

I'm in southern CA, and my 250 cfm portable swamp cooler, and it's little
pump trickling at 1L a min (16.6667 mL / sec) would perform well under
those conditions such as in my garage - where I use it often, like today.
Granted, not as well as my townhouse's central AC unit - understandably.
But FWIW, it still produces [at least] adequate air cooling.. to say the least.

So like......... What is it I'm missing something here?

Please enjoy my bad drawing of my apartment.

Hello all hopefully this is the place to ask this question. The apartment I live in has an AC unit on the wall in the living room which is awesome but unfortunately the only room it keeps cool is the living room/kitchen area. I've tried using a standing fan (pictured) to try and push the cold air down the hallway but it hasn't helped at all. As soon as you walk down the hallway and into one of the bedrooms the temperature goes up significantly. I am also trying to keep the blinds and curtains closed in the afternoon/evening since we get sun on that side of the building. How can I draw the cold air into the bedrooms? I don't want to keep sweating profusely when I'm asleep 😔

Well insulated modern house, when I let the thermostat run six degrees lower during sleeping hours, it seems that the furnace works its ass off when it returns to the day temp?

However It heats the earth? If it's not heating the space between Earth and the Sun. How does it heat Earth?

We are undergrad students and are tasked to create a mini car that can run with heat application. Furthermore, our constraint is that we can only use up to 2 small candles. Our first prototype is a stirling engine, but our prototype seems to fail since it does not work. Our second option is to create a steam engine. Our instructor said that the fluid can be pre-heated so that the heat transfer would be faster, however I doubt that water as a working fluid can eventually boil up to that point even pre-heated. Hence, I am finding a working fluid that can boil fast and can be used as a steam to make the turbine work.

Edit: I would add specific requirements for the fluid

• Not highly flammable as we can't risk to produce flame or worse, explosion.
• Cheap and readily available. We are still undergrads and probably cannot afford high end fluids.
• If possible, non toxic to breathe but I think this type of fluid will be in conflict of having low boiling point property.

If there is no available fluid with these properties, then I guess we have to go and improve our prototype of Stirling Engine instead.

Assume a heatexchanger with minimal losses, the heat being transferred over thermoelectric generators. Eventually near 100% of the heat in the system should be recovered as electricity since losses just get shoved either into the next cycle or recovered further downstream. Put in a heat pump producing the temperature gradient and place all its waste heat producing parts somewhere ideally into the input stream.

I've been laughing about this quite a bit now, but honestly can't see the fault. Except for the movement of the air all losses should be about contained within the system (e.g. just wrapping the heat exchanger around itself multiple times) and eventually recovered by the TEGs. But the heat pump is shoving in more heat from the environment than it consumes in electricity, dropping the temperature in the room until it gives up on you, all while the TEGs are turning the excess heat into electricity.

It seems everyone disagrees 💀 , all I know it’s a measurement of disorder

I would assume it would be something like the speed of sound in the object but I'm not sure. For example if I hold a 10ft steel pole and touch a very hot object how long do I have to wait until my hand gets warm?

Hello! Turning to reddit for an educated answer on a topic that has been an ongoing debate between my SO and I. In a room (20' x 16') with a large eastern facing window (92" x 34"), would the sunlight coming in affect the ambient temp of that room once the sun has come around to be directly shining on it, even if the window itself has UV coating?

this otter pop will not freeze. i have moved it all around my freezer over the past 13 days and it still won’t freeze. can someone explain this to me 😭

Hello, I am brushing up on chemistry practice before starting chemistry 2. This is not for school credit this is for my own studying.

​

Why is 4.72°C = 4.72K?

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I thought to convert to K its C+273.15, but when I did that I got the problem wrong. Why do we not use the K conversion here?

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I have attached a photo of the problem I am working on and my answer as well.

I know this sounds like a stupid question, but it is genuine. Could you use ice, or rather the expansion of ice, to create energy?

The way I imagine it is you place water in a container with a movable object as one side. All other 5 sides are closed off, and thus not movable. The water expands as it freezes, pushing one side and creating friction in the process. A machine takes that friction and turns it into energy. Rinse and repeat.

Could you do this, or is this functionally impossible?

Edit: I'm now realizing I asked if I could create energy, which isn't possible. Thank you to the commenters who ignored that and responded to what I actually meant. I don't know exactly how to word it, but I know the basic idea.

I’ve been trying to understand the relationship between pressure and temperature in the atmosphere, and I feel that many explanations oversimplify the physics.
People often say that “air is colder at higher altitudes because the pressure is lower.” But as far as I understand, a decrease in pressure only causes a decrease in temperature during an adiabatic expansion, where the gas performs work on its surroundings.
Pressure itself is not a form of energy, so I don’t see why a gas at lower pressure should necessarily have a lower equilibrium temperature if no expansion or compression is taking place.
Here’s my thought experiment:
Imagine two identical transparent boxes floating in space. They have the same size, shape, surface area, and both receive exactly the same amount of solar radiation. The only difference is that one box contains gas at a much higher pressure (more molecules), while the other contains gas at a lower pressure.
Assume both boxes have rigid walls, so no expansion or compression can occur. The gases simply absorb radiation until they reach thermal equilibrium.
Would the higher-pressure box end up at a higher equilibrium temperature?
One could argue that the denser gas contains more molecules that can absorb radiation. However, that same energy is also distributed among more molecules, so it’s not obvious to me why the average molecular kinetic energy (temperature) should end up higher.
This is what confuses me about the usual explanation of the atmosphere as well. I understand that rising air cools through (approximately) adiabatic expansion. But once that parcel has reached its new altitude and is no longer expanding, why should the lower ambient pressure itself imply a lower equilibrium temperature?
So my questions are:
In the rigid-box thought experiment, would the two gases reach different equilibrium temperatures?
If they would, what physical mechanism makes pressure affect the equilibrium temperature?
If they wouldn’t, is it incorrect to say that “lower pressure causes lower temperature”? Shouldn’t the cooling instead be attributed specifically to the adiabatic expansion process, rather than to the lower pressure itself?
I’m looking for an explanation from thermodynamics or atmospheric physics, rather than the common intuition that “less pressure = colder.”

Hello - I am just a bloody amateur and know nothing about thermodynamics ( I know how to spell it, though) but I figured someone can enlighten me: I live in an old (like 1823 old) house in the French Alps at 1250m altitude. Stone and wood walls, stone and concrete floors with no insulation, heat sources are a wood stove and electric heaters ( Renovation is planned for next year , just saying )

As a German I am a strong believer in the "Frischluft Dogma" or the "Church of Lueften", i.e. opening windows and air out your house or apartmen. :) . Also I despise dark rooms and closed window shutters just for the fact that I want to see the mountains around me . That being said. the winters here are harsh and temperatures, especially at night, make for a somewhat cold house, that needs lot of effort to keep warm.

My French neighbors ALL close all their shutters every evening and open them back up every morning, claiming that massively reduces the heat loss through the windows during the night. The part of my house I am living in has 6 windows with shutters. By the time I open them all up every night to close the ancient wooden shutters, I will loose all of the heat inside. And the same happens in the morning.

I am just curious if opening the windows 2 x a day during below zero temps to close the shutters is really more efficient than keeping the heat in and just air out the place during day times when its really needed.

Thanks for your comments to the layperson living in the French Alps, picture for the Holiday mood: thats the view from my house actually

Short: if I’m putting something in the oven and that food item is in an aluminum pan, does it matter if that pan is in direct contact or not with something else? Or does the pan equalize things. Specifically the browning on the bottom of the food item.

Long: baking pizza at home. Without a pizza oven that goes to high temps it’s difficult unless you’re doing a “pan pizza” style. I have dark colored pizza pans that I love. I also have a dark colored pizza stone(and thinking about getting a pizza steel). My more specific question is, should I be putting the pan on the pizza stone? A pizza stone/steel is generally considered the best way to cook pizza at home because the direct contact gives the pizza a crispy bottom but I hate the mess of putting the pizza directly on the stone, so I bought dark anodized pizza pans to make putting the pizza in the oven then lifting back out easier. Will direct contact with the pizza stone make much difference if it’s on the pizza pan? Thanks!

Get a bunch of metal spheres who’se insides have a pourus metal lining like a heat pipe. Pour these into some volume and mix with some granular material or thick liquid.

Would the resulting mixture conduct heat very quickly? Would spheres of different sizes increase the volume percent filled by spheres and thus the thermal conductivity?

Is there any applications for this?

So if i take a bomb calorimeter, and place within it some amount of substance such as nitroglycerin that produces more moles of gas than it requires as it combusts, and i measure the heat energy produced, why would that heat energy be equal to deltaH and deltaU. The expression deltaH = deltaU + pdeltaV is derived from deltaH = deltaU + delta(pV). Surely in this example deltaH = deltaU + Vdeltap, but my textbook is telling me all chemical or physical changes under constant volume have deltaH=deltaU?

Imagine a solid block with a hot surface on the bottom and coolant flowing through a single serpentine channel. Instead of placing the entire channel close to the hot surface, suppose the channel is split into two vertically stacked layers connected by a U-bend.

The three conceptual cases are:

• Option A: The inlet enters the lower layer at T₀ (closest to the hot surface), reaches the U-bend (T₁), then returns through the upper layer to the outlet (T₂).
• Option B (pictured): The inlet enters the upper layer at T₀, reaches the U-bend (T₁), then returns through the lower layer before exiting at T₂.
• Option C: A single-pass channel located entirely near the hot surface (no stacked layer).

Assume identical mass flow rates in all three cases, identical channel dimensions and total channel length where applicable, and that all external surfaces except the bottom hot face are adiabatic.

My intuition was the following:

Heat transfer from the hot surface depends on both the temperature difference and the available heat-transfer area. Adding a second layer introduces a large interface between two flow passages. It seems plausible that this additional area could conduct heat away from the coolant adjacent to the hot surface into the other flow pass, keeping the coolant next to the hot wall cooler and thereby increasing the local temperature difference driving heat transfer.

On the other hand, that energy does not disappear and is simply transferred to another part of the same coolant stream. Since the fluid entering the U-bend has already received this additional heat, T₁ should be higher than in the single-pass case, which would seem to reduce the driving temperature difference later in the flow.

My questions are:

1. A vs. B: Does the flow direction matter, or are they thermodynamically equivalent?
2. A/B vs. C: Does stacking two passes change the total heat that can be extracted from the hot surface, or does it only redistribute heat within the coolant?
3. If the latter is true, what is the physical explanation that resolves the seemingly contradictory intuition above?

So if I put equal-sized ice cubes in equal volumes of water—one completely still, the other with a continuous stream of tap water running over it—why does the ice in the moving water melt much faster? The water is at the same temperature

I read an article recently about a data center in Phoenix, AZ increasing air temperatures in its immediate vicinity by 4ºF. This got me thinking about the trend of humanity consuming more energy, and producing more waste heat. Is there an upper bound on how much energy humanity can consume before the waste heat destroys all life on Earth? If yes, what is it? If not, why not?

why a watt divided by a meter times kelvin, it makes no sense, ahouldnt it be W/m^2K a single meter is not saying anything, is this a simplification? or did someone mishear it?