Cold Definition and 395 Threads

What is heat and cold in the atomic scale? Why do things sometimes feel hot and sometimes cold?

Hi guys. As a mechanical engineering final year student, I was assigned to design and build a cold welding prototype to weld just two sheets of metal together by lap joint. Before I actually start the designing process, I tried to cold weld the two sheet metals together by using simple methods...

what is the temperature of cold & hot dark matter?

Does anyone know where I can purchase a temperature sensor that can operate at 200K? Thermistors and thermocouples all seem to fail around 223K.

How to cure a cold?? Usually when I have colds, I eat french fries and they seem to go away within a couple of days. Problem is, it only works with the french fries that my mom makes and she is away this weekend and I have exams next week and I can't take them with snot coming out of my nose...

Hey guys, I'm a bit confused about how hot/cold dark matter plays into our theory of structure formation. Hot Dark matter is relativistic then it decouples in the early universe, and these particles are light and fast and do not form small structures since there is a large mass needed to keep...

Homework Statement Steam is passing a pipe that has cold water flowing through. I need to find the change in temperature from when the water enters the pipe to when it leaves the pipe. Homework Equations First i found the total thermal resistance using...

good afternoon i have a project to build a water dispenser. I'm strugling with heat transfer equations since it's cold that is being transfered. do i use the standard heat transfer equations even for cold? which equations do i use. water will be inside a 100x100x150 (1.5 litres) casing made...

Homework Statement hi everybody i want to make report in cold plasma and what is the difference between cold plasma and the plasma in the sun .

https://www.youtube.com/watch?v=2-vJPOFwz5E I came across a lot of these videos and people say the water is ''vaporized''. I thought about this and why would water become vapor in cold conditions? Isn't it simply becoming snow? What would happen if she had thrown cold water into the air? I

I have a question about how to cool the water that's already in my cup. I already have 3-4 ounces of 70°C water in my cup and want to bring that overall temperature down to 35-38°C. The end solution needs to have 8 ounces of water. I already tried doing this with room temperature water...

Hi, I'm reading about the discovery of the cosmic microwave background radiation and don't understand this part ... What power does a source called with liquid helium produce and how is it related to the amplifier circuits ? I don't get what they did and why ? Thanks !

"Cold welding" question My husband posed an interesting question to me that I can't rightly answer, not being any kind of expert, when I told him about the fact that metals fuse if they come into contact with one another in space. If an asteroid collides with another asteroid, will the two...

What do you guys make of this?? http://www.washingtontimes.com/news/2011/mar/17/nuclear-future-beyond-japan/ It says, and i quote: Which makes me feel at least partly safe posting this on PF. Any thoughts?

Unfortunatley I am getting cold feet in my goal in becoming a engineer... Why, you may be asking, is because everyone I talk to seems to think I have no chance in becoming one! I am a visual learner. Math is also difficult to learn sometimes, Is engineering really not for me because of this...

I'm working on a problem that involves calculating force required to form a component. The problem is as follows (diagram attached): A round aluminium bar, with the initial diameter d0 = 36 mm, has to be cold formed into the component shown in using a combined forward/backward extrusion...

Last winter 2009-2010 was rather harsh in the UK, which caused thousands of families in Wales not being able to afford to heat their homes adequately. The Bevan Foundation has issued a comprehensive report ( http://www.bevanfoundation.org/resources/%2427Coping_with_Cold%2427_Final_PDF.pdf )...

I believe that when refrigerant in an air-conditioner's evaporator boils into gas, the pressure on the refrigerant goes down tremendously. I believe that the drop in pressure on the refrigerant when it becomes a gas causes the temperature of the refrigerant to drop. I believe this because I...

http://www.physorg.com/news/2011-01-italian-scientists-cold-fusion-video.html I know you guys had to have seen this article by now. I am a just a tech guy so most of this is over my head but I am curious what you guys think about it. Is it possible? If you combine Hydrogen with Ni62 or Ni64...

On the Weather Channel you hear all about how a Cold Front is moving in and how there will be a lot of wind...etc. But does anyone know how the cold/wram fronts work? Where they originate? What causes them? Their effect?

Anything to this? Or are these guys quacks? Anybody know? http://www.physorg.com/news/2011-01-italian-scientists-cold-fusion-video.html

it's widely known that a body (whether it's a particle or fluid) moves from a hot region to a cold region. But while doing an experiment, I observed otherwise. The experiment is plunging a hot wire into a beaker filled with water with powder floating on the surface. When I put the hot wire...

So if I leave my steel strung guitar overnight in my cold basement, it goes out of tune on the sharp side. Now if I want to manually tune my guitar sharp, I have to tighten the strings = i.e. put energy into the system and do work. So where does the energy come from to do this in a cold...

Curious question, figured what better place to ask than the physics forum. So I just picked up a used hot tub. Was running great when I bought it. Filled it up with water, turned it on, started its cycle. It can take over 24 hours for the tub to reach 102 degrees. There's a 12 inch...

Homework Statement I am so confused with speed of sound. would sound travel faster in cold or warm air? if you put mathmatical equation in, v= 331 + (0.59Tc) then it would travel faster in warm air. but another theory says that sound travels faster in denser medium and cold air is denser...

Hello forum, I have a metal wrist watch made of stainless steel and titanium (I think) and I was wondering why it is sometimes warm and sometimes cold (or colder than my body temperature it even gets unconfortable). I was thinking, is there something like a threshold body temperature where the...

I have a heated room beside an unheated garage. If I open a door between the 2 spaces does the heat go out to help warm the unheated garage or does the cold enter the heated space for cooling the heated room?

Hello PF readers, Could anyone enlighten me on this specific field of research in physics? I am particularly interested how new/old this field is, current developments, major theories/models/predictions motivating the research, obstacles if any, the saturation of the field? Thanks in...

I am wondering why water is used instead of air for the cold temperature source for a thermo cycle. My guess is the higher specific heat, which means the condenser unit can be smaller, and the mass flow rate less, which reduces the overall cost. Are there any other reasons to choose water...

is it possible to make a cold (room temp) charged gas? would be nifty to use in a heat pump. instead of using compressors you could use fields to compress and decompress the gas

This may seem like an odd forum for this question but I couldn't find an answer anywhere else. Why is it always recommended to rinse the dishwashing liquid and bleach with cold water, rather than hot, when cleaning a jacuzzi tub. Doesn't hot water dissolve and rinse better? My guess is energy...

Hello, I came to consider the following problem, and cannot seem to find the right way to tackle it. It is not homework, merely a question I'd like to address out of personal curiosity: Consider two volumes V1 and V2, each assumed adiabatic, and linked with a valve. V1 is considered...

My friend and I are doing table top fusion for our science fair. We can not figure out a sutable replacement for lithum crystals either than magnets. We need independat varibles, because our teacher says that just 2 magnets is not good enough. Also, it has to be cheap and can be handled by 13...

EDIT: We are looking for someone to clear things up for us! An engineer friend of mine and I are having a debate about heat vs cold. Basically I am saying you can't 'add cold' to a system you can only add or take away heat and for some reason he is disagreeing. Chat of Gchat/AIM ****...

Is it possible for heat to transfer from a colder atom (slower moving) to a hotter atom (faster moving) I know that hot and cold are not really appropriate words to be using here. My reasoning is from kittel thermal physics, From an entropy standpoint, The most probable...

Hi all. I am now working on the uniaxial cold drawing on the plastic sheet (polybutylene succinate, a semicrystalline polymer). After uniaxial cold drawing, as expected, strength increased along the drawing direction/ machine direction (MD). Strength and elongation at break drastically...

Any literature on the big bang usually describes the initial moments as hot and dense. The laws of thermodynamics point to a universe where entropy is increasing, so given the assumption the universe is a thermodynamically isolated system, this implies a low entropy big bang. given that minimum...

- Hello. ... New to the site. Had been searching for "Physics" focused forums, with an attached meteorological element, and found this one.I've been looking into and investigating the "notion" that main "tractive" force *, might have a great deal to do with main and broader cold air mass both...

Ok i get that hotter air is less dense , but when light goes from hot air to colder air we are dealing with the same atoms it is just that the photon will have less collisions , why would the angle of re-emission change for the photon just because it is having less or more collisions in the...

Can anyone explain to me the cause of this massive cold water region in the north atlantic. Is it winds stirring up cold deep water (ekman wind?) Is it a natural variation in currents bringing colder water to the surface? Is there any relationship to the regions north and south of it...

Ok, i need some serious help here... I need to cool air... this is something that involves motorsports, and i want to ask people that have knowledge way beyond me, so i found this forum, hoping someone here can help me... We are running air through a 3 inch diameter pipe... roughly...

I have some difficulties on calculating the reduction on cold rolling process but mi signs is negative. Is that normal? Cheers

Hello everyone, Heat passes from high to low, molecules pass from area of high concentration to low concentration, pressure everything. I was wondering why this was the case. I mean I can think of it like a force reaching terminal velocity, but what about heat does it have a force?

I am trying to figure out how to get cool air. Say, if I have a fan and ice cubes. Should the ice cubes be in front of the fan(air blowing at them) or back of the fan (fan sucking). When I did it, I couldn't feel the difference.

Dark matter: The invisible force The temperature of space may hold the key to solve problem of missing matter Dark matter, the "invisible" mass that scientists believe makes up a large part of the universe, can be explained as being mass that is at one end of a cooling process that all matter...

I have a cold work Nitinol wire, my supervisor ask me to do heat treatment at 700 degree celcius after that quench in ice water.He tell me that after heat treatment, the wire will acquire the shape memory properties, but i have repeat for few sample the wire could not function. when i put the...

Hi I was just wondering why we use ice cold solvent when performing a filtration before vacuum filtration? What exactly does it do? Like ice cold alcohol? I know it allows filtration to be more efficient, but how exactly?

Hot can be cold, and cold can be hot... What ? Has anyone ever experienced http://www.wired.com/wiredscience/2007/10/the-bizarre-eff/" , "Ciguatoxin produces toxic effects by activation of voltage-dependent sodium channels, resulting in hyperexcitability, decreased conduction, and prolonged...

Okey, simple question. As written in the title, I'm really not sure how this should work. Should hot air need more energy to compress than cold air, is it the other way around or is there no difference? This is asked because I need to find out if a physical system could work or not... Any...

In my search for an answer I found a post regarding car batteries but it didnt offer me anything I was looking for. My question, or the a step toward the correct question is how exactly are cold cranking amps on any particular battery determined. At first I speculated it was the amount of or...