Hot Definition and 572 Threads

Homework Statement In principle, does a hot gas have more mass than the same gas when it is cold? In practice, would this be a measurable effect? Homework Equations E = γmc2 The Attempt at a Solution Since there's more energy, there's more mass. But I don't think these effects would be...

Hello, I often read that hot dark matter is constrained by structure formation issues. But I'm now wondering why it is not constrained by the CMB data itself because such hot dark matter should belong to radiation (with density evolving as 1/a^4 rather than 1/a^3) so for instance when we...

Hello physics forums I'm looking to make a food delivery bag and to keep the food as hot as possible as long as possible. I want to use the cheapest materials I can find. My knowledge is limited and so far my plan is to sandwich some cardboard between aluminum foil. I was then going to line the...

do you think copper based grease on the threads of a hot dipped galvanized pipe would likely noticeably(naked eye, no measuring equipment) speed up corrosion of the galvanized pipe in normal environments such as buried in typical soils, maybe slightly more corrosive locations than urban areas...

hey! EDIT: I didn’t post this in homework help because there aren’t any computational questions, it’s just conceptual My assignment scenario consists of a star (blackbody) surrounded by an expanding shell of hot gas. I’m given its spectrum and it is a continuous emission spectrum. Emission...

In the 19th century Lord Kelvin made the first numerical calculation of the age of the Earth not based on the Bible.From his initial guess that the Earth started as a molten rock and that today the temperature of the interior increases at a certain rate as you approach the center, he got an age...

We have a glass containing 0.5 liter (0.5 kg) of water whose temperature 100 degrees Celsius. We also have an ice cube with mass 0.01 kg and temperature -10 degrees Celsius. The cube is put into the glass. The glass is then insulated from the outside world, until the cube has melted. What will...

We know that solar corona is heated up although we don't know yet the mechanism. I was wondering which other type of stars, else than G2, in the main sequence suffer of the same effect? Thank you!

I noticed something when making my breakfast that seems totally counterintuitive. If I add frozen berries that are separate in the pack to my porridge, as I'm heating it, the berries instantly form a solid, icy mass that I can lift out as one block. I can't understand why the berries all...

Hi everyone I'm new around here and I wonder if anyone can help please. I'm taking hot air off the chimney stack inside a factory at a temperature ranging between 700 and 400 degrees going through a 4 inch stainless steel pipe with 3mm wall thickness. This pipe line will be about 35 meters long...

It has been an unusually hot summer where I live. I am not surprised to be getting ads for 'room coolers' due to this. However are not such devices contrary to well known physics? In regions where hot summers are usual. air conditioners are used, they pump the excess heat outside. How though can...

I want to measure the emissivity (or more correctly the absorbtivity) in the wavelength range 1 - 10 micrometer of very hot (~1000 degrees Celcius) ceramic materials. At room temperature this is typically done using an FTIR spectrometer with a gold coated integrating sphere. But for very hot...

I searched for "hot mirror film" on alibaba and ebay with no luck. Only seller I found was selling such films meant for car windows. For that reason it was too thick and a bit expensive because too big. I got one but yeah, it's too thick. I figured I would find few Alibaba sellers for glasses...

Red dwarf stars are main sequence stars but they have such low mass that they’re much ' cooler' than stars like our Sun. Then Simple question here : Sun is cool or hot??

Hello, If two bodies, who say start with ##T_{cold}=T_c## and ##T_{hot}=T_h## and then they are brought in contact with one another and then after some time they both have the same temperature. What would be the entropy of the entire system? Also another quick question, I've looked at some...

Homework Statement A freshly-forged iron horseshoe, with a mass of 0.549 kg is dropped into a 0.281 kg iron pot which contains 1.60 kg of water at 21.4 oC. After the horseshoe, pot and water reach thermal equilibrium they have a temperature of 29.8 oC. Assuming the pot and the water were in...

Hello, I have the following hot water system. I have a water heater with a pressurized cold water inlet. A re circulation line is taken near the farthest fixture passed through a circulating pump and back to the heater inlet. When calculating pump head, do I calculate pressure drop in the entire...

I'm talking hotter than T = 6000k. The higher the temperature, the more the curve in the attached figure would shift to the left (while at the same time getting higher). So the intensity peak would eventually fall back into the invisible portion (very small wavelength this time) of the...

Homework Statement (a) Explain how heat is lost from a hot surface to the surrounding air. The Attempt at a Solution We will assume as there has been no other stipulation that the effect of radiation is negligible and thus we are taking purely about conduction. We will also assume as there...

I placed a hot metal lid on a cool surface. When i tried to pull it up, it had a lot of resistance, i had to really try to pull it up. I could hear sounds under the lid, I'm guessing it was boiling water. What do you think could have caused this resistance?

Homework Statement According to the standard assumptions, there are three species of (massless) neutrinos. In the temperature range of 1MeV < T < 100MeV, the density of the universe is believed to have been dominated by the black-body radiation of photons, electron-positron pairs, and three...

Why is entropy lost by hot water less than the entropy gained by the cold water?From perspective of energy,why is it better to take water and heat it to a temperature than it is to mix hot water and cold water to get a particular temperature.

Why does a tungsten filament light bulb (or any heated metal for that matter) emit EM radiation (both visible and infrared) - is the EM radiation due to vibration of molecules or electron excitation?

Homework Statement My youngest son likes a hot shower, and wants to stay in the shower as long as possible. We do not have an on-demand water heater. He is a small boy, so he doesn't need that much water. The incoming water supply is at 45 deg F and our water heater is rated at 45,000 BTU/hour...

Greetings! I did the famous "Mass Lifter Heat Engine" experiment in which a mass is put at the top of a piston enclosed within a cylinder. The cylinder is connected to an aluminium canister of air and the air inside this canister expands and contracts the piston with thermal contact. We had 2...

I am filling my circular hottub, and charting the water level height. Its sides have a small, constant slope from vertical - i.e. it is a truncated, inverted cone. Imagining an ideal hottub of unlimited height*, the water level will always be increasing - but at a decreasing rate - it will...

Homework Statement A cup of hot chocolate of radius r and height H is completely full. The density ρ and specific heat C of chocolate are known. The cup is very well insulated so that heat is only exchanged with the outside room from the open top. The chocolate is initially at temperature T0...

Homework Statement A hot air balloon is released from the ground & rises up with a constant acceleration of 4 m/s^2. When it is 16 meters above a sandbag is dropped. What is the time taken for the sandbag to hit the ground? Homework Equations v^2=u^2+2as v=u+atThe Attempt at a Solution...

The title says it all. I would like to know how to calculate the time for boiling water to cool off. Assuming the temperature of the room is not changing and there is a constant degree of air flow over the water. Really I would just like to know how to go about calculating this. Thanks in...

How exist voltage between hot and ground? How we are connected to ground through wood floor, building when we use tester screwdriver?

What is 4 times hotter than -4 degrees Celcius? A. -16 degrees Celcius B. -1 degrees Celcius C. 12 degrees Celcius D. 16 degrees Celcius https://www.physicsforums.com/threads/how-much-warmer-is-10-degree-celsius-than-5-degrees-celsius.731713/

(Mods: Please move to 'general discussion' if more appropriate.) I went to order a book this morning on Amazon. The hardcover was a bit pricey so I clicked on "paperback" and suddenly the author's name had changed . . . to "Booby Brown." Given the book was serious non-fiction this seemed a...

In my labs we use hot plates with a 0-10 temperature knob. The hot plates don't have a temperature monitor, so i have no idea how hot each number can increase it or how hot it is at the time. Sometimes i have labs where i have to heat something to more specific temperatures or else the reaction...

In my textbook it says:"in the hot-wire ammeter the pointer stands at a definite reading when the temperature of platinum-iridium becomes constant and the wire stops expanding. That is achieved when the rate of heat radiated by the platinum-iridium wire becomes equal to the rate of heat...

Do hot Jupiter's violate Kepler's laws?

According to this paper https://arxiv.org/pdf/1701.03128.pdf is this a fudge factor or can we have a mixture of energies for DM. Abstract. Various particle physics models suggest that, besides the (nearly) cold dark matter that accounts for current observations, additional but sub-dominant dark...

Homework Statement A hot-air balloon stays afloat because hot air at atmospheric pressure is less dense than cooler air at the same pressure.If the volume of the balloon is 500 m3 and the surrounding air is at 60◦F. What is the maximum load (including the weight of balloon, but excluding the...

Why do hot dishes dry faster than cold ones? Does a high temperature mean more energy and so it evaporates or something? Or does a high temperature lead to the water molecules being more 'slippery' and so there is more run off? Thanks PF!

So I've heard that increasing pressure in water would make the molecules more compact and then eventually become a solid. So it's possible to have hot ice. But isn't it also true that as pressure increases, the temperature increases as well. For example, if I increase the force per volume, the...

Hey guys, is it possible to replicate the sounds produced by exhaust gases in a car by using only hot air? Thanks in advance for your responses.

Homework Statement Why are stars hot? Homework Equations Non specifically, it's a conceptual question. The Attempt at a Solution I have always heard that stars are hot because (as a quick very basic example) stars are large collections of mass which collapse in on itself. Eventually the...

My wife likes the old school bulb look so I picked up some C7 string lights for the tree. This year we got a real tree. I plugged the light string in and after a few minutes the bulbs got so hot I couldn't touch them. Are these things really that safe and ok to put around a tree? I must imagine...

Homework Statement A blacksmith drops a 0.7 kg horseshoe of iron at a temperature of 1200 ̊C into a bucket of 0.5 L of water at an initial temperature of 30 ̊C. How much of the water boils off? Assume the bucket absorbs none of the heat. Homework Equations I believe Q = mc delta(T) is what I'm...

Hello people of PhysicsForum Apologies in advance if my prefix selection is inaccurate and for my absolute physics noobness. I know no physics jargon so I'm sure my question will be phrased in the same way a 10 year old might. So here is my silly, trivial question: First of all, remove all...

Homework Statement [/B] A nail is heated in a bunsen burner flame and is about to be dropped into a beaker of water at room temperature. a) Which of the two substances (nail or water) would you expect to initially have: i) the highest internal energy ii) the highest average kinetic...

First of all, even I did mentioned Solar Cooker, the main goal is to reach most temperature of 500ml of water in 30 minutes. Basic information that I have is some material with different thermal conductivity. I seek for simple english language and a bit complex physics language. The idea of...

Hi guys, I was just thinking about something and I'd love to get your opinion. How much energy do you think is lost from water pipes getting hot and releasing that energy into the air? In a three bedroom house there are probably a lot of hot pipes releasing heat energy. Do you think some sort...

Hello, I have a physics question about saunas and hot stone technology which I hope someone can help me with. I recently experimented by reconstructing a "sauna" found at a Bronze Age site in Scotland. We heated stones (sandstone) in fire pits and transferred them to the circular 'sauna'...

I have a project which i need to cool down certain quantity of hot water. I need to cool down water of around 25 litres at 50 Degree celcius to 30 Degree celcius, Static water, not flowing. (or incoming 50 Degrees - Outgoing 30 Degrees with approx 1.5 gallons per minute flow rate) time...

Hi. Temperature is movement on a microscopic scale, and movement leads to time dilation. So what happens if we heat up a clock? Let's for example assume a pendulum with negligible thermal expansion, such that all other thermal effects on the period can be neglected. Will it run slower? What...