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. A

    B Temperature of an accelerating system

    if i take a box and fill with solid metal that has a temperature T . what if the box is accelerated to the speed of light . would T -> 0 ?
  2. Aafia

    What is the effect of temperature on enzymes in poiklotherms

    Since enzymes have particular temperature on which they are able to catalyze the reaction and increasing the temperature above optimum can damage enzymes then how does poiklotherms survive as they change their body temperature according to environment unlike homoiothems. Also wouldn't their...
  3. Omish

    What temperature do thermocouples show? Static or Total?

    What temperature does thermocouples show? Static or Total? And also in formulas for example Q(dot) = m(dot) * C_p * (T2 - T1) which temperature should be used precisely?
  4. R

    Why the temperature of a moving jar of gas doesn't increase

    Homework Statement Why doesn't the temperature of a moving jar of gas increase? Homework Equations Average KE is proportional to temperature The Attempt at a Solution This is just an extension of a problem my friend sent me, and I'm stuck on why even though average velocity is increasing...
  5. E

    Book of T-S diagrams, or the like

    Hello - I just starting out in chemical engineering. I hold a batchelor's degree in Chemistry, and am making a transition to ChemE. This isn't for any class, just in general for reference, does anyone know of a good book that is primarily just thermodynamic charts, like T-S diagrams? I have...
  6. I

    Constant heat flux or constant temperature

    Hey all, first time posting! So I'm having trouble with understanding the differences between the constant heat flux and constant temperature condition when not in a textbook. Some research I have begun working on involves a strip of heat tape sandwiched between two aluminum plates which are...
  7. P

    Low temperature production with compressed air

    Suppose, there are two cylinders of compressed gas, say air. Both are at same temperature and pressure and the amount too is same. Now, contents of both are released but in a different way. One has been released directly and the other has been released through compressed air turbine having a...
  8. G

    I Exploring Time Dilation: The Effects of Temperature on Clocks

    Hi. Temperature is movement on a microscopic scale, and movement leads to time dilation. So what happens if we heat up a clock? Let's for example assume a pendulum with negligible thermal expansion, such that all other thermal effects on the period can be neglected. Will it run slower? What...
  9. C

    Can I Calculate Temperature Release from Energy Change in a Body?

    Hi, I would like to ask a question, if I may: if I have a body with a calculated Inertial moment at time t0, that in a space of time delta t changes, there's a variation in its kinetic energy, right? How can I calculate the released temperature in that elapsed time? Is that energy all lost in...
  10. C

    Calculating Temperature Change from 20°C to -20°C: Homework Question

    Homework Statement in this question , it's not stated that whether the temperature change from 20°C to -20°C or -20°C to 20°C . I'm confused... Homework EquationsThe Attempt at a Solution I think it should be changing from 20°C to -20°C so delta T = (-20-20) = -40°C , am i right ?
  11. M

    Temperature of a radioactive material

    Hi all! I have a certain quantity of a radioactive material (e.g. 1 kg) in the open space. How can I calculate the temperature of this material as a function of time? If it is useful, we can consider a beta decay material. Thanks a lot.
  12. E

    Temperature Coefficient of Resistance and Specific Heat

    I am trying to estimate the amount of electrical power needed to heat up a material from 20C to 1000C in 20 seconds. Assuming it is 18sqin and 3mm thick, I used the specific heat which was given as 0.78 J/gC and weight 11.39g (from the destiny of 3.26). 0.78 J/gC x 11.39g x (1000C - 20C) /...
  13. shina

    Time & Temperature: Proportional or Inverse?

    Hey I m new here. I hope u all will cooperate with me. As I have read much about proportionality in science. So can I say that when time increases temperature also inreases or decreases. So time is proportional or inversely proportional to temperature.
  14. T

    Why the temperature remains constant at the boiling point?

    Why all liquids vaporize on boiling point instead of the temperature gradually increasing along with vapor pressure and more liquid atoms evaporating? Does it have anything to do with formation of vapor bubbles?
  15. C

    Change in length due to temperature

    Homework Statement in the notes , i was told that ∂A is the resistance of aluminium rod...I'm wondering the change length of steel rod that we can 'see' is ∂ st or ∂T(st) ? Homework EquationsThe Attempt at a Solution I think the change length of steel rod that we can 'see' is ∂ st ?
  16. Niladri Dan

    Temperature in Space: The Kelvin Scale

    The Kelvin scale states that the temperature is a measure of the kinetic energy of the particles(molecules) of the system. But what is the temperature of a system where there are no particles...for example free space, far away from the stellar civilisation...
  17. D

    A Carrier concentration temperature dependence; semiconductors

    Hi all, I'm reviewing device physics and I would like to understand how majority and minority carrier concentrations for both N- and P-type substrates change with temperature. My reference, Pierret's Semiconductor Device Fundamentals, has this figure: and I want to generate curves for all...
  18. T

    Calculating combustion temperature of mixture

    Hey guys, I'm trying to write a small article that very simply explains some of the math involved with a rocket engine. I'm not looking for a very accurate answer so I tried the following method 1) Stoichiometry on the fuel which was sugar and saltpeter and their respective enthalpies of...
  19. E

    How to calculate blackbody temperature from radiance band?

    I know how to calculate blackbody radiance in a spectral band from a temperature by integrating (or summing) planks function. How can I do the reverse? For example, I have a Radiance of 1000 W/m^2/sr in the 3-5um band, I'd like to be able to calculate 666.6K.
  20. S

    Calculating heated rectangle temperature rise

    Hi I have a question about temperature rise and thermal conductivity. If I have a small 1 watt heater (3 x 3 x 3mm) in the middle of a rectangular block (100x40x70mm) made of a material that has a thermal conductivity of 0.48W/mk, how do I work out the final temperature that the block settles...
  21. G

    Robotics Engineers -- How could a bot navigate by temperature?

    I've seen a bit of research that relies on imaging methods like FLIR for input. My question adds a couple wrinkles: How could a robot Navigate without imaging? I.e., using only local sensors like a thermocouple or array of thermocouples. Extract navigation info from turbulent thermally...
  22. P

    I Determine the temperature of a star via its spectrum

    In the following video (, diagram also given for reference), the professor says that if the graph peaks in a short wavelength, then the star is a hot star (or galaxy) and if it does so in a long wavelength, then it's a cold one. However, I fail to understand this. How does it happen that if a...
  23. Magnetic Boy

    Bosons at very high temperature

    Will all particles be in excited state in boson condensate if temperature approach infinity?
  24. A

    Thermo: Principles behind temperature drop across a valve

    Hi everyone Would like some help here. If I draw a control volume across a valve that I can control the flow area to, and I know the temperature and pressure upstream of the valve, I will know its enthalpy:in. High temperature liquid going through this valve supposedly changes to steam due...
  25. S

    Internal energy in irr. process with molar heat not constant

    I'm a bit confused about the following situation. In a irreversible thermodynamics process the molar heat of an ideal gas changes according to a function of the temperature, say ##c_v=f(T)## (which also leads to ##c_p=R+f(T)##) and I'm asked to determine the heat exchanged during that process...
  26. A

    I Why does temperature always rise in stars?

    Hello everyone, I know that pre-main sequence stars do heat up because of gravitational contraction, and the increase in internal energy (and so in temperature) comes from this shrinking and is governed by the virial theorem (...
  27. S

    Thermal expansion of liquid in a tube

    Homework Statement A cylindrical glass tube (linear thermal expansion coefficient ##\alpha##) contains liquid (volume thermal expansion coefficient ##\beta##). The height of the tube is ##h_{t,0}## and the height of the liquid inside of it is ##h_{l,0}##. If the temperature changes of an amount...
  28. S

    Engineering Moving Mechanical structures: stress, wear, temperature....

    Hi! I am looking for a textbook that explains/describes for moving mechanical structures (such as linkage mechanism, engines, ... and not buildings, bridges, ...) the stresses, deformation, wear, temperature change, ... due to operating. E.g. Linkage mechanism: what are/defines the stresses...
  29. J

    I What is the relation between Temperature and Quantum State?

    Hi folks, Let's pick a simple example, the H atom. We can calculate all spherical armonics, all quantum numbers so we are able to know which are all the possible states of the electron. We know all the values this observables can take. But the question is, let's say we have a handbook of...
  30. Alfreds9

    Calculating air pressure from altitude, RH and temperature?

    Homework Statement [/B] This is a practical problem, no homework question. I'd like to determine pressure (and O2 partial pressure) at altitude, yet following a more realistic real-world calc including measured data like relative humidity (RH) and temperature at that altitude, yet all I can...
  31. Salvador

    Temperature dependant resistor for MAF

    Hi folks, so here's my recent problem, My car has a broken MAF (mass airflow sensor) the semiconductor innards are ok but the very thin metal strip that comes into the airflow tube has become brittle from old age and broken up. I know the MAF works when it sends a low voltage through the...
  32. campeola46

    Finding n and p of semiconductor given temp, NA, ND, and Ni

    I'm doing independent study on semiconductors to prepare for a future class and I'm having problems with some problems that concern finding the n and p of doped Silicon given only a temperature, NA, ND, and Ni. I understand that n*p=Ni^2, but, given that this means that n does not equal ND (and...
  33. jormi

    I Small temperature dependence in diamagnetic material

    Hi everybody! I´m chemist doing new materials and my understanding of physics is quite basic. I have a sample (single phase) of Ba and Ge and it shows diamagnetism in the magnetic susceptibility measurement, however it show a small temperature dependent behavior. As far as I understand...
  34. M

    Why Is the Calculated Temperature of the Universe Different from 3K?

    Homework Statement Two scientists detected the cosmic microwave background radiation at a frequency of 160 GHz. What is the temperature of the universe? Homework Equations peak wavelength x temperature = 2.898 x 10^-3 c = f x wavelength The Attempt at a Solution I calculated the wavelength of...
  35. Schwarzschild90

    Canonical partition function for N ideal gasses

    Homework Statement Exercise 4 in the upload titled Dok1.pdf. Write down an expression for the canonical partition function for N ideal Na2 gas molecules, when the rotational contribution is treated classically, and all inner degrees of freedom are treated quantum mechanically. Use this and...
  36. L

    Finding 2D Fermion Gas U/N with Temperature & Area

    Homework Statement For a gas of N fermions with mass M in 2D in a region of area A in thermal equilibrium at temperature T, we are asked to find ##U/N## in fuction of ##T## and ##a=A/N##. The attempt at a solution I used ##U=\sum(<n_i>\epsilon_i) = \sum(\exp(\beta(\mu-\epsilon_i))\epsilon_i...
  37. GW150914

    I Why do we need "planetary equilibrium temperature"?

    I mean, currently it seems that scientists are using equilibrium temperature of exoplanets (calculated assuming an Earth-like albedo) to determine whether a planet is habitable or not. But aren't there other more accurate ways to determine surface temperatures of exoplanets? I learned Wien's...
  38. P

    How to measure the temperature of liquid in sealed container

    I am not a scientist or particularly good with math or formulas. I have been curious about this for a while, and would appreciate anyone clarifying/correcting me. I have a stainless steel container that can be heated up to 75 degrees celcius/165 degrees Fahrenheit in a bain marie. It can hold...
  39. astrotizio

    A Stellar photosphere temperatures

    Hi all, Star surface temperature determines the occurrence of photosphere, where radiation can escape from star interior due to diminishing gas ionization and radiation absorption. If it was true the star photospheres should have the same temperature and Herzsprung-Russell diagram should be...
  40. striogi

    Writing: Input Wanted The temperature at which flesh burns

    I'm putting together an idea about a weapon (insert hand-wavy science here) that fires extremely high temperatures a very short range (100 feet or so). A Heat Shotgun, if you will. The idea is that this weapon, with a single blast, could turn the majority of a human sized creature to literal...
  41. P

    Fermi Function at High Temperature

    Hello, A question I can't seem to find a simple answer to is, what happens to the Fermi-Dirac distribution at T grows large? Mathematics suggests that it approaches 1/2, like it does when the energy becomes equal to the Fermi energy. Or, are we not allowed to use the F-D distribution for high...
  42. T

    Adsorption and Critical Temperature

    Homework Statement An extract form my textbook: " In general, easily liquefiable gases( ie. with higher critical temperature) are readily adsorbed as van der walls forces are stronger near the critical temperature. Hence 1g of activated charcoal adsorbs more SO2( Tc=630K),than CH4...
  43. Asafish

    How much heat required to raise the temperature of potassium

    Homework Statement At low temperatures, the specific heats of metals is described by the expression ## c=kT + AT^3 ## , where k and A are constants. Here the first term describes the contribution of free electrons and the second the lattice contribution. How much heat is required to raise the...
  44. L

    Is temperature measured in kWh normally distributed over different time spans?

    Are the temperature over 24 hours normally distributed? Over 1 year? Over 15 years? Is there a difference in distribution depending on the time span Are MIN temperatures per day i.e. the coldest temperature measured over a 24hr period normally distributed? Over one month Over one year Over 15...
  45. S

    Calculating the output temperature of a Solar Thermal system

    So say I have a PV-Thermal array and assuming standard test conditions. How would I calculate the temperature of the water coming out of the system? The thermal output of the system is 67.5kWp with a maximum flow rate of 65L/h. Approximately 500m of 3/4" pipes.
  46. S

    What is temperature stability? (Lamination)

    I'm doing some work on solar and I'm reading about properties of lamination materials, particularly EVA lamination. Anyway, one of it's properties is 'temperature stability' but I can't find a clear definition of what this means. EVA lamination is sandwiched in between a solar cell, so I can...
  47. Gerald Kaiser

    Are temperature and pressure related by relativity?

    Since the temperature of a gas is related to its average molecular energy and the pressure to the average molecular momentum, it would seem that a Lorentz transformation would somehow relate the two. Does anyone know of related work?
  48. L

    Can power supplies cause temperature fluctuations....

    can power supplies cause temperature fluctuations in a circuit? Or, instead, are they sensitive to temperature fluctuations in the environment, which can cause temperature fluctuations in a circuit?
  49. KishoreAM

    Temperature Profile -- temperature-length curve of a metal bar

    Guys... If there is a bar, half of it is Copper and another half is Steel (Length wise) and both of its ends are at 1000K and I want to know how to find the temperature- length curve. this was an interview Question by the way.
  50. Elvira

    Calculate the temperature based on Resistance

    Hello experts... I have an experiment pool boiling. The test section filled with DI water, and use thin flat copper as the heater that connected to the power supply. I want to ask how to measure or calculate the heater temperature if I only have the resistance, voltage and current data reading...
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