What is Temperature: Definition and 1000 Discussions

Temperature is a physical quantity that expresses hot and cold. It is the manifestation of thermal energy, present in all matter, which is the source of the occurrence of heat, a flow of energy, when a body is in contact with another that is colder or hotter.
Temperature is measured with a thermometer. Thermometers are calibrated in various temperature scales that historically have used various reference points and thermometric substances for definition. The most common scales are the Celsius scale (formerly called centigrade, denoted as °C), the Fahrenheit scale (denoted as °F), and the Kelvin scale (denoted as K), the last of which is predominantly used for scientific purposes by conventions of the International System of Units (SI).
The lowest theoretical temperature is absolute zero, at which no more thermal energy can be extracted from a body. Experimentally, it can only be approached very closely (100 pK), but not reached, which is recognized in the third law of thermodynamics.
Temperature is important in all fields of natural science, including physics, chemistry, Earth science, astronomy, medicine, biology, ecology, material science, metallurgy, mechanical engineering and geography as well as most aspects of daily life.

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  1. G

    I Why is there no frost below a certain temperature?

    It is 21°F here this morning and no frost on anything not even car windows. I have noticed this before when it gets cold enough there is no frost. Maybe all the moisture freezes out of the air and there is no moisture to make frost? I don't know? At what temperature is there no frost?
  2. C

    What is the change in internal energy after two processes?

    So the question goes like this: find change in internal energy in process 1->2 using diagram. And offered solutions a)-400J b)400J c)600J d)800J. First I found T1 and T2 using (P*V)/T=R and got T1=24K and T2=72K. Then I found n(number of moles) using PV=nRT and got n1=1mol, n2=1mol. Then I...
  3. J

    What is the temperature loss along a duct with hot air entering?

    Hello, I am looking for assistance regarding temperature losses along a length of pipe with hot air entering one. I need to know the temperature leaving the other end of the pipe. I have been able to calculate the W/m-K (in theory but stopped a i knew the answer wasnt what i needed) losses but...
  4. StanislavD

    A Experiments for temperature dependence of persistent supercurrent?

    Imagine, in a mercury ring (superconductivity below Tc=4.15 K) we establish a persistent supercurrent. Then we organize temperature cycles (T-cycles) in the cryostat, from 3 K to 2.5 K and back. According to the BCS theory of superconductivity, the pair density decreases at warming, i.e. a not...
  5. S

    B High Temperature in Gravitational Fields: Exploring the Possibility?

    Sir, heat is proportional to the vibration of atoms. If the vibration of atom is restricted to large extent due to intense gravitational field but has high quantity of total energy in the atom then does it mean it has high tempearture like the stars?
  6. J

    I Trying to better understand temperature and entropy

    If you were to condense all the energy in the universe into a point, wouldn't the temperature be very high, yet the entropy be very low? Also if you were to spread out all of the energy in the universe, wouldn't the temperature be near zero and the entropy be very high? And this makes entropy...
  7. Algr

    Highest useful Fahrenheit temperature?

    I was watching a video about energy storage, and the subject was stuff that was around 1500° celsius, and for the whole video the graphics kept including Fahrenheit equivalents. Now I use Fahrenheit when checking the weather outside. But that doesn't make 2732F° any more relatable a...
  8. K

    I Questions about Curie Temperature Characteristics

    Is the curie temperature of a ferromagnetic material constant? Are there any factors that will raise it or lower it? For instance, what happens if my piece of iron is already in a strong magnetic field? Is the curie temperate higher, then?
  9. FEAnalyst

    Triangular cavity thermal radiation simulation

    Hi, I'm trying to solve a problem involving radiation in a triangular cavity: As you can see, lengths and emissivities of all surfaces are given. For two of them, the heat flux is known and the temperature has to be found while for the remaining surface it's the other way around. I have the...
  10. Astronuc

    High Temperature and Very High Temperature Materials

    A family member shared an article about thermovoltaics being developed at MIT with support from National Renewable Energy Lab (NREL). A new heat engine with no moving parts is as efficient as a steam turbine https://news.mit.edu/2022/thermal-heat-engine-0413 The article mentions that the...
  11. T

    Gas law problem (changing volume, temperature and pressure)

    I can’t quite work my head around this question, I am having a difficult time analyzing the question, I can’t seem to make out what the initial and final conditions are would appreciate all the help I could get cheers
  12. nuclearsneke

    Exceeding the saturation temperature of coolant on the clad for PWR

    Hello there. I have been conducting a thermal calculation of a fuel assembly for KLT-40S reactor (a small modular PWR-like reactor installed at the floating nuclear power plant "Akademik Lomonosov" with electric power of 35 MWe.) and obtained some interesting results. It seems that cladding...
  13. L

    Finding both temperature and the amount of gas added

    The volume of the cylinder is ##V=\pi r^2 h=\frac{7\pi}{250}\ m^3## the number of moles is ##n=\frac{15}{16}\ mol## so from ##PV=nRT## we get ##P=\frac{nRT}{V}=25975.5\ Pa##. Now, for the second question, it should be an isochoric process so ##V_2=V_1## and ##P_2=P_1+0.8P_1=\frac{9}{5}P_1## and...
  14. Zakariya

    Changing the Temperature in an MCNP code

    Hello everybody. I would like to ask a question; if I change the dimensions and densities and the material number identifier ZAID to a specific temperature. Does MCNP change automatically the volume of the cells? or I have to change the volume of each cell manually and indicate it in the cell...
  15. C

    I Wave in phonon as "forward and backward" movement vs temperature

    My first question here, so maybe not adequate or in the wrong topic, excuse me. I try to understand vibrating light harvesting antenna in biochemistry but it is a question of physics. We talk about a molecule with an emission spectra peak of about 650 nm. In classical physics electrostatic and...
  16. SherLOCKed

    I Will the upcoming experiment PICO measure kSZ temperature anisotropy?

    I know for sure PICO will be measuring polarization anisotropies with high fidelity. In addition, the PICO science paper shows that it will make full-sky Compton-y maps but the plots are mostly limited to l=1000. Will PICO be able to measure kSZ temperature anisotropy at l=3000?
  17. L

    Finding equilibrium temperature when there are phase changes

    If there weren't phase changes occurring I know that the temperature equilibrium would be ##T_e=\frac{m_{ice}c_{ice}T_{ice}+m_{w}c_{w}T_{w}}{m_{ice}c_{ice}+m_{w}c_{w}}##. Now, by repeating the reasoning to get the above formula (##\sum \Delta Q=0##) and adding the phase changes of the water...
  18. jones1234

    I Estimating Vertical Wind Speeds: T_a, T_s, & P_a

    Hi all, I have some data from an automatic weather station, with recordings of both 2m air temperature and 2m air pressure and also the surface temperature. Is it possible to estimate vertical wind speeds between the AWS and the surface based upon this data? Imagine T_a = 15 degrees and T_s =...
  19. S

    I Understand the Thermodynamic Identity: Is This Correct?

    I have a question about the Thermodynamic Identity. The Thermodynamic Identity is given by dU = TdS - PdV + \mu dN . We assume that the volume V and that the number of particles N is constant. Thus the Thermodynamic Identity becomes dU = TdS . Assume that we add heat to the system (we see that...
  20. mcas

    Calculate Conductivity Temperature Dependence in Semiconductors

    I have to plot the conductivity dependence of temperature and I have problems with obtaining the right dependency of \mu and n. But let's focus only on carrier concentration first. For n I used the third equation. From what I understand N_D is a constant. I want my plot to look like this: But...
  21. GhostLoveScore

    Construction Temperature inside a weather station enclosure

    Hello I have a digital thermometer that I put into a wooden enclosure. It has horizontal holes drilled into its sides all around to let air in. On the bottom there is an opening around 1/3 of the width, like in attached photo. And I was thinking about certain thing. When I put a bare...
  22. fluidistic

    I Extremely strange consequence of the speed of heat value

    By chance, I have read a paper that left me in shambles. I would like you to help me figure out if it makes sense or not. I tried to follow Bridgman's logic, without a complete success. The extraordinary claim is that, if you start with a system consisting of a 1cm^3 copper cube where 2 faces...
  23. mark_bose

    How to explain the effect of temperature profile on feedback coefficient?

    Hi all, I'm trying to derive fuel temperature coefficient in a TRIGA reactor using a monte carlo code. When i do that, if i assume a radial temperature profile along the core, i obtain smaller value (-7pcm/K) than the one achieved with uniform temperature (-9pcm/K). More in detail: in my case...
  24. P

    Comparing Cube A & B's Temperature Change

    I know in this case cube A would heat up faster, but would cube B eventually reach the same temperature?
  25. O

    I How did Charles obtain his law when absolute temperature wasn't define

    Hi all These days I am refreshing my knowledge on the concept and measurement of temperature. One way of defining temperature is in terms of how it is measured. This can be done by observing the variation of some properties which vary linearly with the hotness(temperature) of bodies. I studied...
  26. PainterGuy

    B Extrapolation of relationship of temperature and volume for gas

    Hi, Originally, the absolute temperature was thought to be around -273 Celsius around 1750 and it was the result extrapolation of of ideal gas law as shown below. I find it hard to phrase my question. But the question is how come they were so confident that the relationship between the volume...
  27. Hananism

    The distance traveled by a molecule at a specific temperature

    I found this equation: and kB and T are Boltzmann constant and temperature, respectively.
  28. K

    Safety of plastic spoons, etc. below their advised maximum temperature?

    I like using polypropylene dishware e.g. spoon, and storage box. I can see that from its label sometimes the maximum temperature recommended is 110 degree C or 120 degree C but it usually doesn't go away from this range. By common sense, I will never heat the polypropylene dishware directly but...
  29. I

    Clarification on magnetization and temperature

    Summary:: Hello, I am doing a report for my IB course that requires some mathematics to be done. I have found this thread incredibly useful and I would like to reach out to ask for some clarification. My experiment recorded the magnetic flux density directly above neodymium disc magnet, at...
  30. jaumzaum

    I Refractive index vs Temperature

    I was studying radio waves phenomenons and found this on Wikipedia: "Tropospheric ducting is a type of radio propagation that tends to happen during periods of stable, anticyclonic weather. In this propagation method, when the signal encounters a rise in temperature in the atmosphere instead of...
  31. FEAnalyst

    Heat sink - calculating temperature at the base

    Hi, I've checked the literature but couldn't find any formulas or examples for this particular problem involving heat sink with straight fins: As you can see, I want to assume: - power at the bottom surface - convection (known ambient temperature and heat transfer coefficient) at the...
  32. R

    Please help me calculate the wire temperature due to this current

    Hi, I need to calculate the temperature of a wire, due electric current passing through, and I have no idea how to do that. I need it for a device that I want assemble. I'm using one single thread (strand) of speaker cable, like you can see in this picture: Again, Just a single thread that...
  33. Andrea Vironda

    Is there something happening below 0°C in this daily temperature graph?

    Hi, I notice from the graph that every night when the temperature reaches -2/-3 °C the curve change first the slope and then the concavity. Is something special happening?
  34. S

    Looking to create a temperature rate of rise table for air

    How did you find PF?: Google l was asked how hot would our IT space get if we lost all air conditioning. The space is 20' x 15' x 10', We keep set point at 70 F and have 80 kW of load. Assuming this exists in a well insulate container with 20 racks of equipment. Doesn't have to be perfect but...
  35. E

    Effect of temperature on vibrational frequency of a violin string

    Variables: Dependent: Vibrational frequency of violin string (Measured using mobile tuning app) Independent: Temperature in which string is plucked (Measured using infrared thermometer) Controlled: Violin String, Tension of violin string, Length of violin string, Method of plucking...
  36. Huzaifa

    Chemistry Effect of temperature change in Le Chatelier's Principle

    The effect of temperature change in Le Chatelier's Principle is given by the equation $$ \log \left(\frac{\mathrm{K}_{2}}{\mathrm{~K}_{1}}\right)=\frac{\Delta \mathrm{H}}{2.303 \mathrm{R}}\left[\frac{1}{\mathrm{~T}_{1}}-\frac{1}{\mathrm{~T}_{2}}\right] $$. How to derive $$ \log...
  37. D

    I Getting a sauna to a certain temperature - faster with more rocks?

    We've been discussing what it takes to get a sauna to heat to 240F. Most sauna heaters will have some stones to provide mass to hold heat. The question is whether lots of stone mass will make it easier to reach higher temperatures. My argument is that it does. Imagine heating a room using a...
  38. theycallmevirgo

    Industrial CO2 laser temperature management

    Here it is specified that optimum operating temp for industrial C02 laser is within the range 59 °F to 77 °F. This is what is generally specified online, but it leads to a number of questions; How is this measured? Does it refer to the whole unit, or the point of emission of the beam, or some...
  39. binis

    I Does Dark Matter Have a Temperature?

    A black-body absorbs and emits radiation if heated, but it does not reflect or transmit radiation.What is the temperature of dark matter?
  40. B

    Finding transition temperature of Landau ferroelectric

    So for part a, I separately minimized F wrt ##\theta## and ##P## and got the following. $$\frac {\partial f} {\partial \theta} = a_{\theta}(T-T_{\theta})\theta + b_{\theta}\theta^3 - tP = 0$$ $$ \frac {\partial f} {\partial P} = \alpha(T-T_P)P -t\theta$$ $$ P = t\theta \alpha (T-T_P) $$ Then...
  41. L

    At what frequency can Planck's law be used to determine the temperature?

    Hi, I am not quite sure if I have calculated the homework correctly :-) I proceeded in such a way that I first calculated from which frequency the two terms are equal, and thus the equation results in zero. Then I figured a relative accuracy of 10% equals a relative error of 90%. So I...
  42. P

    A Temperature of gas in a cluster

    The following link states that: "since kT ~ mpv2. A typical velocity dispersion 700 km/s implies T ~ 6 x 107 K from this source alone." How did they get 6*10^7K ? When I try this, using mp = 1.67*10^-27 , k =1.38*10^-23 I end up getting 84 as a final answer, nowhere near 6*10^7. Can anyone...
  43. G

    I Passive radiative cooling of surfaces below ambient air temperature

    Apparently, it's possible to cool surfaces below ambient air temperature by passive (no input of energy required) radiative cooling to harvest water from the atmosphere: https://www.science.org/doi/10.1126/sciadv.abf3978 There's also a Nature paper about this effect, but behind a paywall...
  44. duchuy

    Maximum flame temperature during Combustion of CH4

    Hi, I have to calculate the maximum flame temperature of the reaction above. The answer is 4805K but I didn't manage to obtain that answer. Please help me find my error, thank you so much! The values of C are below the solution attempt.
  45. M

    A Why low temperature is better in many precision experiments?

    Hello! In many precision experiment, especially those overlapping with quantum computing techniques, such as trapping a few ions in a Paul trap, they use cryogenic systems (around 1K). I am not totally sure I fully understand the advantage of that, compared to room temperature. For example, a...
  46. A

    Engineering Noise Floor/Device Temperature Problem

    Hi everyone, I would like to get some help with the following problem. I'm not sure if my answer is feasible. Thanks. My attempt at a solution: I used the noise power equation: Pn= 10*log10(kTB) and converted the -100 dBm to dBW by subtracting 30 dB to get -130 dBW. Then I tried to find the...
  47. J

    A How to calculate the temperature change of a laser-irradiated material

    I am looking to approximately calculate the temperature change of a sample that was exposed to a laser pulse. Experimentally, we know the optical absorption, reflection, and transmission, as well as the source parameters for our laser system. I realize that I will have to make approximations...
  48. V

    Temperature rise without heat energy?

    If I look at the specific heat equation mentioned, then I would be inclined to think that without heat energy being added to the gaseous mass its temperature cannot rise. But, if some form of energy like chemical energy in gaseous mass could be directly converted to internal energy of the same...
  49. K

    Calculation of the rise in the temperature of a truck brake

    The text gives the answer as 92ºC. The answer is arrived at by doing ##Q=Mgh=mc\Delta T##. But it is unclear to me if they are the same. I checked the coefficient of friction and it definitely seems to be considerable. Is the entire PE lost by the truck going to result in increasing the...
  50. Ale_Rodo

    I Why is Entropy defined as a fraction of heat over temperature?

    Can we make sense out of the formula of entropy like we do for density (like "quantity of mass per unit volume")? What's the sense of Q/T? Couldn't it be something else? Of course it probably is a 'me-problem', but I haven't studied Thermodynamics deeply yet and was wondering what Entropy...
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