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. T

    Maximum temperature reached by gas in expansion

    Homework Statement 1 mole of ideal gas with internal energy U= 3/2 RT , expands from initial volume Vi = 1/10 Vo following the equation p=(− po / Vo ) V +po . Find (a) the highest temperature reached by the gas during the expansion and (b) the maximum amount of heat taken in by the gas...
  2. R

    Difference between vibrational, rotational and electron temperature

    I am trying to explain the following statement in my own words... Would it be correct to say that.. I am unsure if a vibrational state is simply a different energy state or something more specific? Do the electron temperature, vibrational temperature and rotational temperature all...
  3. Borek

    Critical temperature, or: Is the supercritical liquid a phase?

    Somehow I am worried it is a can of worms, but I will still try. This started with a student confused with statements describing critical temperature for the gas/liquid equilibrium. Some books and sources state it is the highest temperature AT which it is possible to liquefy the gas just by...
  4. ervays

    -40 to 70C Degrees Special Refrigerator

    Hi all, I'm trying to find a special refrigeration device that can goes from -40 Degrees to 70 degrees. I need this machine for a laboratory to test sensors in differente temperatures. Does anyone knows where can I find something like that? Kind Regards Vicente
  5. Physics Dad

    Stellar Radius & Effective Temperature

    I have a question for my Astro homework and I am a little unsure as to whether I am going in the right direction Question Using an expression that relates luminosity, size and temperature of a star, and assuming all Main Sequence stars have the same mean density, determine the relationship...
  6. G

    Boil by increasing temperature or reducing pressure?

    Which one is cheaper to do if I have a reactor at 45 bar, 80C and wish to distill a substance before it enters another reactor at 15 bar, 150C?
  7. AndyCh

    B Some questions about terminology

    I thought this would be the most logical way to post this, but give me some grace if it is not because this is my first time posting on this site (then relinquish the grace and tell me how to do it properly haha). First: When a physics problem says "sliding past point P" does that mean it stops...
  8. Drakkith

    Newton's Law of Cooling When the Temperature of the Air Isn't Given

    Homework Statement You come across a dead body at 3 PM. Its temperature is 83.6 F. 30 minutes later its temperature is 78.6 F. How long was the guy dead before you found him? Homework Equations ##\frac{dT}{dt}=-k(T-Tair)## T(0) = 83.6 F T(0.5) = 78.6 F The Attempt at a Solution This is a...
  9. H

    A Hall coefficient's finite temperature experiments in metals

    There are lots of measurements showing strong temperature ($T$) dependence of Hall coefficient ($R_H$) in correlated materials (eg. cuprate superconductors and other oxide materials) and such plots are available in many recent experimental papers. However, I could not find any $R_H$ vs $T$ plot...
  10. C

    How to find mass given pressure and temperature

    Homework Statement A 3-m3 rigid vessel contains steam at 10 MPa and 500 degC. The mass of the steam is? I know this question involves using a thermo-table, I'm just very confused on how to find mass from the given information. Homework Equations Maybe PV=nRT The Attempt at a Solution I...
  11. ervays

    Temperature, humidity and gas sealed box

    Hi, I'm working on my thesis and I need to calibrate some gas sensors that I'm building. I need controlled conditions(temp, RH and a known gas concentration) in order to calibrate the sensors. I'd love to know some idea to make a sealed box in which I trace and vary those parameter. I've...
  12. Sheroff

    Which Pressure Gauge Determines Saturation Temperature in a Closed Loop Pipe?

    water is flowing in the closed looped pipe equipped with preheater. there are pressure and temperature gauges before the preheater and after the preheater. which pressure gauge should i use to know whether the outlet preheater temperature has reached the saturation temperature?
  13. Q

    I Temperature impact on laser emission

    Hi everyone, I'm trying to understand why laser diodes need a stronger input current to start lasing when their temperature increases. If I tried to add thermal transitions to the rate equations governing the evolutions of an atom quantum level populations (let's say ##n_{up}## and...
  14. T

    Calculate uncertainty in pressure, temperature and time?

    Homework Statement [/B] After doing a lab on air compressors, we were asked to calculate Error in Pressure, Temperature and time measurements taken (all at 30 second intervals). We took pressure and temperature values at time = 0,30,60,90,120,150 and 180 seconds. We repeated the experiment 5...
  15. Djok1234

    Help me to solve my house swimming pool temperature problem please

    What's up guys. Is there anyone who can challenge to solve this theoretical problem that can help to solve my house problem? There's an empty outdoor swimming pool that has width a, length b, and depth c, such as its volume = abc. The temperature of outside is -3 C° and we are trying to fill...
  16. D

    NTC and comparator to detect temperature trip point

    In "The Art of Electronics" the following is said: "A comparator in a circuit is a handy device that switches its output according to the relative voltages at its two input terminals. There is a temperature sensing device, a thermistor, which decreases in resistance by about 4%/°C. So we’ve made...
  17. F

    Skin temperature increase due to radiation absorption

    Hello, I am trying to figure out how much the human skin temperature would increase when the skin is illuminated by radiation of a certain intensity (W/m^2). We can assume that the skin has an emissivity and absorptivity both equal to 1. For instance, imagine the skin illuminated by the sun (I=...
  18. P

    Temperature-dependent entropy

    Homework Statement As you know it's finals time and I desperatly need help with one physics task (it's not my main subject, but I still have to pass it -.-). Here it is: According to data below count temperature-depended entropy and entropy itself for reaction: CH4 + 2 O2 = CO2 + 2 H2O CH4...
  19. Lacplesis

    Entropy and temperature question

    Hi folks, I have a question, I will first write down some old truths and then ask what is unclear to me. Now we know that Boltzmann's constant is the average kinetic energy of one molecule of ideal gas, related to its temperature T. The German scientist Clausius defined entropy change of some...
  20. C

    Equilibrium Temperature with three substances

    Homework Statement If a block of 250 grams of lead (specific heat (c) =130) at 315 degrees celsius is placed in a 200 gram aluminum (c=900) calorimeter cup containing 900 grams of water (c=4.1), and the calorimeter and the water are both initially at 15 degrees celsius, what is the equilibrium...
  21. Kara386

    Temperature fluctuations in helium

    I'm about to do an experiment on second sound in superfluid helium. Reading the lab manual it says we will generate it by putting a heater into the fluid and then passed an AC current through it. What we are going to measure is apparently the 'normal fluid fraction', which I guess under the two...
  22. G

    What is the equilibrium temperature of a collector plate?

    Homework Statement You would like to put a solar hot water system on your roof, but you're not sure it's feasible. A reference book on solar energy shows that the ground-level solar intensity in your city is 750 W/m^2 for at least 5 hours a day throughout most of the year. Assuming that a...
  23. ElPimiento

    Equilibrium temperature of some ice and steam

    Homework Statement "A well-insulated bucket of negligible heat capacity contains 120 g of ice at 0°C. If 20 g of steam at 100°C is injected into the bucket, what is the final equilibrium temperature of the system?" Homework Equations $$Q_{fus} = m_{water}L_{fus}$$ $$Q_{vap} =...
  24. BH1988

    Fe2O3 Thermal Decomposition Question

    Hi, I've been asked to heat a sample that contains Fe2O3, amongst some other things, to a temperature where Fe2O3 will decompose. I am unable to find the temperature at which I would need to heat the sample and I'm not entirely convinced this is actually possible with the equipment I have...
  25. Delta Force

    Temperature and Power Plant Output?

    This is probably a very basic engineering question, but I'm from an energy policy background and the resources I've found (such as this) are quite detailed. Internal combustion engines such as automobile engines and aircraft (jet and piston powered) produce more power in colder environments and...
  26. AliSkully

    Help with understanding equilibrium & temperature

    Can someone explain why when you increase the temperature on an endothermic reaction, it yields more products? Is it because the activation energy is higher in an endothermic reaction, so there is more time for the products to form? also why does decreasing the temperature yield more products in...
  27. D

    Why when I freeze a container does the humidity go down?

    I am working on a project to stockpile and freeze photographic film and paper for later use. This is not for academic or commercial purposes, but just for personal use. I've been experimenting and am stumped as t the following: I place a package of film in a ziplock bag in an environment of...
  28. A

    Finding Specific Heat of Unknown Metal

    Homework Statement I'm asked to find the specific heat of Metal X in this simulation: http://group.chem.iastate.edu/Greenbowe/sections/projectfolder/flashfiles/thermochem/heat_metal.html Mass of Metal X = 120 g Temp of Metal X = 220 degrees Mass of Water = 30 g Initial Temp of Water = 20...
  29. T

    Lower kinetic temperature implies population inversion?

    I was just wondering: why does lower kinetic temperature imply population inversion? I've read this is true in a few (astrophysics) texts regarding molecular clouds, although this seems to be a more general result that I haven't really read an entire explanation for. Nevertheless, do you have...
  30. Clara Chung

    Exploring Temperature and Energy: Answers to Common Questions

    1.If temperature is just a measurement of KE, can a system with higher temperature contains lower internal energy than a system with lower temperature? 2.Can energy flow from an object with higher temperature to an object with lower temperature even if the internal energy of the object with a...
  31. Claude_mar

    Predicting internal temperature with or without HVAC

    Hi, how to predict indoor temperature with or without HVAC? I have the internal temperature's value, the external temperature's value and the temperature of HVAC's air output. I want two function, one with HVAC on and other with mode off. Hp: start time 0, end time Tend. Tend has values from 0...
  32. binbagsss

    Plot Heat Capacity vs Temperature for a 2 state system microcananonical ensemble

    Homework Statement I have ##C= NK_B (\frac{\epsilon}{K_B T})^{2}e^{\frac{\epsilon}{K_B T}}\frac{1}{(e^{\frac{\epsilon}{K_BT}}+1)^2} ## and need to sketch ##C## vs. ##T## Homework Equations See above The Attempt at a Solution I have ##C= NK_B (\frac{\epsilon}{K_B...
  33. G Cooke

    I Can Temperature Changes Alter Humidity in a Completely Filled Closed System?

    We know that for a closed system, isobaric heating decreases the humidity and isothermal compression increases the humidity. But assuming that we start with the volume completely filled with humid air, is it not true that any increase in temperature must also increase the pressure? If so...
  34. A

    I Determining the total energy released by a compost pile

    The heat source for this experiment is a compost pile (1 cubic meter), I know that the inside of the pile will reach approximately 50C for 2 weeks or so. Right now it's winter so the temperature will stay around 0C (average). The thermal conductivity of compost can vary greatly but in this case...
  35. T

    What happens to wavelength as temperature of air increases?

    Homework Statement what happens to wavelength if temperature increases? Homework Equations V= lambda * frequency The Attempt at a Solution I'm guessing since no change to frequency is stated?.. and I know that the speed of sound increases as temperature increase. The wavelength would have to...
  36. A

    I Determining the energy released by a flame

    I've found a lot about using water to find the amount of heat released by something but the experiment I want to run would take about two weeks to complete so that's probably not a viable solution for me. I know what the temperature will be and that it will remain mostly constant, is there...
  37. gonadas91

    High temperature Superconductors: Cuprates

    Hi everyone, I am about to finish my PhD and need to start thinking about trying to move somewhere else. One line of research that caughts my attention is that of the cuprates, and the study of their phase diagram. I would like to know if someone can suggest a very recent book or review article...
  38. I

    Calculating saturation and dew point given pressure and temperature

    Hi guys and gals. Hobbyist, not a student. I've had great input here in the past. Thank you in advance for any direction and help figuring this out. -Seth- 1. Homework Statement I'd like to learn how to calculate relative humidity, saturation, and dew point under differing pressures and...
  39. A

    B Temperature in the space between planets of our solar system?

    I know that the overall temperature of the universe is microwaves at 3 Kelvin or so from the Big Bang, but is this mostly for deep space? Or is this pretty much the temperature in our solar system also, assuming a coordinates some distance away from any of our planets but still within our solar...
  40. parshyaa

    How anders celcius defined temperature scale.

    What made anders celcius(founder of °c temperature scale) to use water as a bench mark for measuring temperature, why he used water's freezing point as 0°c and boiling point as 100°c, is there a reason or he just used water so that it can work easily.
  41. A

    Temperature physical or chemical change

    If you Increase or decrease temperature and change states of matter, that's a physical change. But are there any circumstances where temperature can cause a chemical change? Like if increasing temperature could break the bonds between the atoms and separate them? And I don't mean a combustion...
  42. Timmykuku

    Does Ambient Temperature Affect Cold-Blooded Animals' Size?

    Since cold-blooded animals, such as lizards, turtles, &c., take on the temperature of their environment, can we expect them to linearly and volumetrically expand/shrink in warmer/cooler environments? In addition, can we expect them to follow the simple equation: ΔV=βV0ΔT, for some volume...
  43. Saharka

    Otto cycle combustion heat question

    I have been trying to determine the efficiency of an ideal Otto cycle based on the compression ratio of my car and the heat of combustion of gasoline and I think I'm not entierly wrong but there is something quite off. When trying to calculate the temperature of the combustion stage my result...
  44. R

    Why is vaporisation rate increased by a decrease in pressure

    In my textbook, it says that the rate of vaporisation can be increased by (a) increasing the temperature or (b) reducing the pressure. I understand why an increase in temp can lead to more molecules breaking away from the liquid and entering the vapor state. More temp = more energy = more...
  45. physea

    Role of pressure and temperature in chemical reactions

    Hello! I have a feeling and I would like to know if it is true. I feel that if a reaction between two gases, takes place in high temperature only (perhaps with the presence of a catalyst), then if we increase the pressure high enough and keep the temperature low, the reaction may still take...
  46. FQVBSina

    Heat transfer by radiation and Temperature difference

    Hello all, this is related to a project that I am working on. It is not directly related to the project but as part of it, I thought it would be a good idea to check the temperature difference that I need to maintain in order to effectively transfer a certain amount of heat between the TH in a...
  47. N

    Calculating Internal Energy & Temperature Change of Ideal Gas

    Homework Statement What is the change in internal energy (in Joules) of an ideal gas that does 4.675x10^5J of work, while 2.95x10^6J of heat is transferred into the system and 7.95x10^6J of heat is transferred from the system to the environment? Calculate the change in temperature of the two...
  48. Chadi B Ghaith

    I Find Oven Temperature at various moderate mode?

    Hello, I want to convert gas unit into oven temperature (Fahrenheit, Celsius). Which formula I can use? Also I want to know at which oven temperature we can assume it as moderately high or cool temperature??
  49. onargaroberts

    Impact of the engine thermostat temperature setting on engine efficiency

    Will a four cycle, internal combustion engine have greater thermal efficiency with a relatively cool jacket water temperature, say 160 degrees F, or a relatively hot water jacket temperature, say 190 degrees F? These specific numbers are only important in as much as they are commonly available...
  50. D

    Electromagnetic Radiation temperature

    Is there a meaningful way to convert the energy of an electromagnetic wave to a temperature? I mean this more along the lines of how the universe has a temperature of 2.7 kelvin due to electromagnetic radiation. I'm honestly just curious to determine the temperature of the universe after nearly...
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