Cold Definition and 381 Threads

For me 76°F is cold and at 69°F I begin to shiver. I'm used to temperatures ≥ 90°F almost every day. In fact my room has been lately getting at 94°F at night while 86°F at the outside of the house (at night). Therefore, I'm very sensitive when it comes to drops in temperature. Anyway, what...

Homework Statement (c11p34) You pour 160.0 g of hot coffee at 75.0 oC into a 230.0- g glass cup at 24.0 oC. If they come to thermal equilibrium quickly, what is the final temperature (in oC, enter deg in asnwer box)? Assume no heat is lost to the surroundings. Homework Equations (I don't even...

Hi! I wonder what makes the often black "painted" aluminum heat sinks for electronics cold by the touch? To me a shiny heat sink would work better because then all the incoming wavelengths are reflected. A black heat sink would however absorb all the incoming wavelengths because that is by...

Hi Guys, Can anyone provide links, books which explain the mathematical background of the field theory that explains the current accepted ^CDM model of the universe? Thanks Adarsh

http://www.cnn.com/2014/08/29/justice/cold-war-spy-dies/index.html?hpt=hp_t2 Finally. Now it's time for Whitworth to go. http://en.wikipedia.org/wiki/Jerry_Whitworth These people got a lot good men killed. https://www.youtube.com/watch?v=hccc-t-ZumQ

Working on a project where we have been asked to utilize waste heat from a combustion process in order to increase the temperature of oil in a separate process. The hot air from combustion is at 340C and the oil is at 22C with a target temperature of 65C I have not seen any hot air heat...

This question has puzzled me for a long time and there have been many kinds of answer for it. The most sensible explanation I have heard is this one. http://physics.stackexchange.com/a/33026/40382 But then I found another explanation at...

Joe Silk is one of the co-authors. One expects large voids in the distribution of galaxies because of the cobwebby way dark and ordinary matter have condensed. A large void comparatively close by (within a few billion LY of us) could cool ancient background light passing thru on its way to us...

Can someone explain the process?

Hello , I was always wondering about this phenomenon : when i take out a cold bottle from the refrigerator , after a few seconds (lets say at room temperature) the bottle is surrounded by water. the question is - why is it? where did the water come from ? is it should happen with...

If heat flow is the momentum change from a faster moving atom or molecule to a slower moving one, and momentum is mass x velocity is it possible - for a very limited amount - for heat to flow from a slower (colder) heavy atom to a faster moving (hotter) atom ?

did anyone observe that a balloon gets cold when stretched quickly,why?

I just read Source: http://www.princeton.edu/~oa/winter/wintcamp.shtml#Food This counters my intuition Can someone explain this to me? Thanks

Two papers went up today regarding infrared all sky surveys by WISE and 2MASS that affirm the CMB cold spot - http://arxiv.org/abs/1405.1555, A Supervoid Imprinting the Cold Spot in the Cosmic Microwave Background; http://arxiv.org/abs/1405.1566, Detection of a Supervoid Aligned with the Cold...

In an AC circuit, we know that the polarity inverses, and what i know is that the flow of current also will therefore inverse.. which means that the live will become negative and the neutral will become positive.. What i can't understand is how the polarity inverses but the live is still the hot...

gelatin, celluloid paraffin and ivory all exhibit phosphorescence at lower temperatures why is that?

Generally for bathing purpose, we heat water to higher temperature say T1 than the temperature at which body is comfortable say T0 (is T0 = 70 degree Celsius?) & add some quantity of cold water to it to have the temperature of water = T0. Is the process energy efficient? What is the best...

Why do many claim the universe as a cold place? If it is the natural phenomena then how does formation of stars take place?

Hi everyone, In a current project, I'm curious about the risk of silicone tube cold welding when used with a solenoid pinch valve, such as = http://cfnewsads.thomasnet.com/images/large/454/454667.jpg What is the likelihood silicone tube will cold weld at the pinch point, if the pressure is...

Consider any of the latest maps of the temperature fluctuations of the CMB. Such a map can be considered a 2 dimensional topographical map of the surface of a sphere, high points hotter, low points cooler. Consider the contours that divide such a map into the two regions, fluctuations hotter...

I know that Cold Air is more dense than the warm air, so for example: If a car was accelerating facing a hot air, it will face less air resistance. But if it was facing a Cold air, it will face more air resistance because the cold air contain more mass per volume for each particle. It will face...

"cold capacity" We are taught the notion of heat capacity in undergraduate physics and how different materials can hold a different maximum of heat energy per unit volume. Is there an opposite notion? Obviously heat is energy, so cold is just lack of it... but my intuition tells me that if I...

Homework Statement You are going on a long trip in the summer with a dessert that must stay cold. You have a cooler with the interior dimensions measuring 13 in x 8.5in x 11 in. The cooler has 1.75 in of polyurethane foam insulation. The dish is in a water tight container so food getting wet...

If someone stepped out into the vacuum of space, would it really be cold? Wouldn't you need an atmosphere to feel the heat or cold? Say your in intergalactic space. Approximately how fast would it take to freeze to death? I am assuming the only way your body heat could leave would be through...

Hey guys. I was studying up jet-engines and their performances with varying ambient temperatures and found myself stuck on something that is probably very trivial. What I've read online and in my notes is all generally the same - that as temperature falls air density rises and as such more...

http://www.iflscience.com/chemistry/hot-water-freezes-faster-cold-and-now-we-know-why I thought that this had never been shown to happen with closed containers. I always thought that this was an issue of open containers allowing for evaporation and hence a smaller amount of frozen water, and...

Homework Statement A heat pump requires 385 W of electrical power to deliver heat to your house at a rate of 2410 J per second. How many joules of energy are extracted from the cold air outside each second? Homework Equations COP= Qc / W . This was the only equation I could find...

Hi Guys, I am not an engineer and was hoping someone could help me with a question I had about piping in cold weather. I am setting up a temporary 4" Bauer water pipe that I need to keep from freezing. It will be outside (non insulated) in February in Ohio. I am expecting temperature...

Homework Statement Consider two systems which together comprise an isolated system, but are initially not in equilibrium with each other. The temperatures of the two systems are T_1 and T_2 and the internal energies are E_1 and E_2. The systems are separated by a diathermal wall and only...

I'm guessing the alcohol in beer would evaporate extremely slowly in cold temperatures like a fridge. I hear a lot of people say otherwise, so I'm wondering if it even evaporates a noticeable amount in 24 hours?

Can a Thermocouples cold junction can be electrically manipulated. Can a Thermocouples cold junction can be electrically mimicked to be a colder one; thus is it possible to make refrigerator out of thermocouples? electrons flow from hot to cold junction right ? can anyone give me link to more...

What's the difference between cold moving air and hot moving air? For instance, suppose you put two fans, of the same type, each in one room. One room is cold because the walls are covered in ice and one room is hot because due to the effect of heaters. Turn both fans on and the air flow, the...

Recently I was wondering why deodorant is cold when its comes out of the spray can. Some explanations say that it is because of a change in pressure. But looking at the ideal gas law T = PV/nR and both n and R are constant. And for every decrease in pressure there should be an increase in volume...

So awhile ago I was thinking about wind. Sometimes wind is hot but when I think of wind I usually think of cold wind. Wind seems to be fast moving particles and I know based on the kinetics theory of gases KE = \frac{1}{2}mv^2 = \frac{3}{2}kT Maybe, I'm making a wrong assumption but...

In some texts about plasmas, the plasma oscillations are discussed at the extreme of no Thermal motion. One example is the one in wikipedia: But I can't accept that approximation.Because it is assuming that we have a kind of motion called thermal motion and other kinds which arise from other...

Let us assume there is a single atom in a vacuum chamber which is kept at near absolute zero. Now assume the system is closed and that the chamber is large enough such that the atom cannot diffuse far enough to reach the walls. Neglecting other stochastic effects, what do you think the atom's...

Hi, I am trying to think of a way to attach my water baffle/cold trap to the bottom of my base plate. The baffle is attached to a diffusion pump, meaning that I need a good seal between the plate and the baffle. I was thinking about drilling holes in the baffle and half way through the base...

i'm leaning towards sustainable and renewable energy sources, upon seeing the Ironman film of Jean Favreau, i come to theory that maybe the arc reactor that Stark industries manufactured and designed is quite feasible through cold fusion reaction... is it possible? if it is, please provide any...

I am currently in training to become an analyst using thermal imagery. In the studies I have been introduced to cold sky reflection on thermal imagery, however the instructor explained it as a surface 'reflecting the cold from the sky' which, as far as I'm aware, doesn't fit with the second law...

So I was at a ski-resort last weekend and this question just came to me out of nowhere. Hot air usually rises. Shouldn't that logically lead to high altitudes being warmer than low altitudes?! It's true for the ocean, but air seems to defy this law. Why is that?

Say a pair of twins both feel like they are coming down with a Cold or flu. One twin wisely comes home from work takes a hot shower, warms the house temperature a bit, has a good meal and goes to bed early with her iPad. The other twin heads out to a night club and has the time of her life...

Homework Statement I need to find out which freezes faster--hot or cold water--without doing a lab. Just by thinking and considering laws and theories and properties we have learned about. Homework Equations N/A The Attempt at a Solution It seems like it would be cold water since...

So this isn't homework, but it is for a class and I don't know how to go about this... I have to figure out if hot or cold water freezes faster. Any ideas?

When in reality, blue light is the higher energy.

Apologies if this has been addressed earlier. A common belief is that a cold temperature (say 0 Centigrade) feels colder when relative humidity is higher. Is there any underlying physical reason for that? As far as I can tell, the differences between dry air's and water vapor's thermal...

Why actually does "hot" water freeze before cold water? This sounds very basic but believe me I can't come up with a single feasible reason

Just got back home from the Kona side of Hawai'i. Wow. What a freakishly cool place that is! Day one, snorkeling. Saw so many fish...blue, yellow, stripes, red, dots, skinny, long, buck-toothed, bug-eyed, orange, green,...wow. Just, wow. Day two, long hike along beach. Admired the flowers...

If you lie on the ground at night with no cover, you get cold rather quickly. Much of this is due to energy loss by radiation. At night in a dry climate, the temperature of the sky can drop to -40oC. If you are lying on the ground with thin clothing that provides little insulation, the surface...

I am coming up with a new wing suit that combines soaring with jet pack propulsion in such a way that even valley dwellers can fly, and possibly commute in this fassion. I fear compressed gas alone will not have enough thrust for long enough. One concept to think of is to charge a...

Can I assume that even though I am a bit of a germ phobe that my body is on a daily basis exposed to cold germs? I try to be careful about keeping my hands clean and not sticking them in the wrong places (mouth, nose, eyes ?). If I am constantly exposed to cold germs and I don't always get a...