Temperature Definition and 1000 Threads

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. 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...
  2. 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...
  3. 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?
  4. 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...
  5. 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...
  6. 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...
  7. 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...
  8. 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...
  9. 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?
  10. 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...
  11. 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...
  12. P

    A How is the Temperature of Gas in a Cluster Calculated?

    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...
  13. 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...
  14. 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.
  15. 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...
  16. 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...
  17. 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...
  18. 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...
  19. 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...
  20. 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...
  21. O

    Simulation Code for Earth's Historical Temperature Record

    I am new to the field of climate change. Are there publicly available simulation code for Earth's temperature history, going back, say 2000 years, with a resolution on the order of years? Thank you very much.
  22. S

    Does Resistance change wrt temperature include effect of size change

    Changing the temperature of a metal changes the resistivity. But It also changes the size of a sample under test. Does the change in size have an additional effect on the resistance or is that already factored in ?
  23. U

    B Physical temperature and antenna temperature

    I have read some documents on the subject, but until now, unfortunately, I still do not have a good understanding of them, most likely due to personal shortcomings that start from physics. In this regard, I would like to try here to expose some doubts that will almost certainly appear very...
  24. ikihi

    I Compressing gas with piston: reasons for temperature increase?

    So when volume decreases, pressure increases according to Boyle's Gas Law and the ideal Gas Law. In other words, compressing gas into a smaller volume increases the vapor pressure. And also, According to Gay-Lussac's Law and ideal Gas Law, when pressure increases on a gas, temperature also...
  25. AppleiPad556

    Correlating albedo with temperature?

    As mentioned above, I wanted to devise an equation that can relate the colour of a surface to the temperature on the surface. I tried using the general definition of albedo and combining it with the Stefan-Boltzmann equation (see above, Relevant Equations). However this means that the higher the...
  26. C

    B Cooling the room with a ceiling fan and skylight window

    Hello, So I know that a ceiling fan either operate clockwise (winter mode) or counter-clockwise (summer mode) and while the fan is meant for just moving air around, I'm wondering if utilizing a ceiling fan and an opened skylight window only a few feet near the ceiling fan would help move the...
  27. Poetria

    Multivariable temperature variation while swimming in a hot spring

    I have computed ##T_x## and ##T_y## and evaluated it at the point (20, 20). ## \frac {-450*x}{x^2 + y^2 + 1)^(\frac {3} {2}} - \frac {420*(x + 10)} {(x + 10)^2 + (y - 20)^2 + 1)^(\frac {3} {2}}, \frac {-450*y}{x^2 + y^2 + 1)^(\frac {3} {2}} - \frac {420*(y - 20)} {(x + 10)^2 + (y - 20)^2 +...
  28. pixelsnpings

    Calculating temp rise caused by electric arc in an enclosed space

    Summary:: Given a known closed space/apparatus ( e.g. constant volume, pressure, density, current, temperature, voltage, spark gap distance - let me know if I missed something) how would I compute the change in gas temperature. Hello, Given a known closed space/apparatus ( e.g. constant...
  29. S

    I (See image) At what distance does the temperature of the Corona decline?

    My astronomy textbook includes this graph of the temperature of the Sun's Corona versus the distance above the photosphere. It appears to go up from 4,500 K to over 1 million K at 20,000 km above the photosphere. But at what point does it come back down? Or does it not? Does that mean the...
  30. river928323

    Maintaining Component Temperature with Water Bath

    Using water bath to maintain temperature of the component
  31. Istiak

    Calculate the volume change with gas temperature for this piston in a cylinder

    Solution attempt : Option : I am sure that my work is wrong. But, I must add solution attempt in PF that's why I just added that. How can I solve the problem?
  32. George Jones

    What Causes Extreme Temperature Swings in My City?

    Yesterday's high temperature here was 38.4C (101.1F). The early morning low on 15 Jan 2020 was -44.2C (-47.6F). In the last 18 months, my city has had a spread of actual temperatures of 82.6C (148.7F).
  33. Krokodrile

    Chemistry Work, temperature and energy in a constant pressure process

    So, the Cp and Cv its very confusing for me. But, i understand what's its happening in this process, so, i use the logic and first i obtain a ecuation for obtain the final temperature ecuaticon: Q=m*C*△T Q=m*C*(T2-T1) T2=(Q+T1)/(m*C) If the process its in constant pressure, i use the Cp valor...
  34. M

    Temperature vs moisture content to sustain a fire in a given material?

    So I've been trying to start a fire in which was successful for 10 minutes then died down due to high moisture in the leaves and branches. Which made me think of this phenomenon. is there a graph relationship to burning an organic, non-metal material that is well defined in relation to the...
  35. xpell

    Could a high / very high temperature nuclear reactor operate in Venus?

    Hi. I'm just a curious person with high-school-level scientific knowledge. However, I was wondering if a specially-engineered Generation IV high or very high temperature (800-1,000ºC) nuclear reactor could work in Venus using the local atmosphere at 450ºC as "coolant", just like a "typical"...
  36. F

    Metals as Infrared Reflectors and their Temperature

    Hello everyone. I have reading about IR radiation, reflectivity, and emissivity of materials. Metals, in general, seem to be excellent reflectors or IR radiation (they are like infrared mirrors. That said, why do they get so hot when they are left in the sun? A metal roof cannot be touched...
  37. J

    I Temperature of the Universe based on the ΛCDM Model

    Using Jorrie’s calculator we can get the following T vs. t graph up to z = 20,000: In a log-log plot the above curve is represented by the red solid line in the figure shown below: The dashed line shows results for the small a limit using the equation T = 2.725 K / a. Here are some...
  38. Dario56

    Maximum non - PV Work at Constant Temperature and Pressure and Reversi

    When we talk about systems at constant temperature and pressure, maximum amount of non-PV work can be extracted if process is carried reversibly and in that case it is equal to change in Gibbs energy of the system (decrease in Gibbs energy if system does non - PV work, A.K.A work is extracted...
  39. T

    A Photon self-energy in the finite temperature field theory (real -time)

  40. F

    Instantaneous Gas Compression: temperature increase?

    If I a have a gas confined in a certain initial volume Vin at a certain pressure Pin and at a certain temperature Tin, and istantaneously compress it down to a final volume Vfin < Vin, how do I calculate the increase in temperature? Assume I know the exact pressure curve (P vs. V). The system...
  41. J

    Relative Humidity and Temperature Changes when adding Heat

    Can anyone help me with this? -How much heat must be added to 3.5 m3 /s of moist air with a dry bulb temperature of 10°C and a relative humidity of 60% to raise the temperature of the air by 17°C? • What will be the relative humidity of the air once this heat is added? • What is the power...
  42. J

    How to calculate initial pressure and temperature - adiabatic process

    Im confused on working backwards so to speak to find adiabatic work. To find work for this adiabatic process, I either need to know the change in temperature OR the initial pressure (I think?). The issue is that I don't know either the initial temperature nor the initial pressure so I am not...
  43. D

    Calculating Hot Air Balloon Volume & Lift

    Volume of hot air ballon V=((4/3 pi R^3)/2) + (1/3 pi h (R^2 + r^2 + Rh) = 2956.24 m3 Balloon: R=9m h=15m r=1m m = 750 kg H = 5000m T = 373 K p1 = 101300 Pa p2 = 50650 Pa M(air) = 0.029 kg/mol F = mg - 7350 N
  44. Mohammad Sakib

    Why the temperature of a car does not increase with velocity?

    We know temperature is a measure of average kinetic energy of molecules/particles of a system. Now if a car starts to move, its velocity increases so does its kinetic energy. Therefore all the molecules are gaining velocity too. Shouldn't this increase the temperatre as average kinetic energy of...
  45. G

    Absolute zeros other than temperature (e.g. pressure)

    Hi. A version of the third law of thermodynamics states that no system can be cooled down to absolute zero temperature in finitely many steps. But what about other quantities, for example pressure: Is it possible (in principle) to evacuate a system up to the last gas particle, or would this...
  46. M

    The effect of temperature on phosphorescence

    I had read somewhere that as the temperature increases, its lifetime decreases. But there was no further explanation. Of course, I don't know if it's true yet.
  47. S

    Thermodynamic Axioms: Establishing Temperature, Internal Energy & Entropy

    Is the purpose of the 0th, 1st & 2nd Laws of Thermodynamics simply to legitimate the thermodynamic properties of Temperature, Internal Energy & Entropy, respectively? It seems that all these laws really do is establish that these properties are valid thermodynamic state properties and the...
  48. J

    Finding temperature change, thermodynamics first law

    So I calculated the final and initial pressures using the given eqns, ended up with the final pressure of 96629 and initial pressure of 62639. Then I used the PV=nRT eqn to calculate the final and initial temperatures. T=P*V/(n*1.5*R). I got an initial temperature of 81.79 and a final...
  49. J

    Find rate of temperature change using heat capacity, density and area

    So first I found rate of heat change using the above equation, with T=883K, e=1, SA= 6*l^2=21.66 Now dQ/dt=746593.71 W Now I am not sure entirely what to do next. They give density so I likely have to get the mass from that, M=pV,=1.9^3*4037=27689.783 kg. My issue is that I don't know how to...
  50. J

    Calorimetry - finding the final temperature of a system of ice and water

    So all of the ice melts and I am guessing it then warms some so Q=mL+mc(change in T) for the water that cools down Q=mc(change in T) Q_cold = -Q_hot so -mc(Tf - Ti) = mL+mc(Tf - Ti) My issue is that I have 2 unknowns. I don't know the specific heat capacity of water and I don't know the...
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