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. D

    Why is a drinking bird colder than the ambient temperature?

    In a drinking bird, water from the wet on the outside of the head evaporates, causing the vapor inside the head of the bird to cool. This reduces the pressure of the vapor at the top, allowing the higher pressure in the lower bulb to push up the column of liquid. But the bird's body (including...
  2. K

    Chemistry Understanding Heat of Neutralization in Acid-Base Reactions

    I have a couple of questions related to this task. The reaction that I proposed was this: NaOH(aq) + HCl(aq) <--> Na+ + Cl- + H2O (l) where as the solution manual have this net reaction, as nothing will happen with the Na+ and Cl- ions: H+ + OH- <--> H2O. I assume these reactions will...
  3. D

    Thermodynamic possiblity for outlet temperatures of heat exchanger

    I have a heat & mass balance diagram wherein there is a shell and tube heat exchanger to recover heat from hot exhaust gas using cold water. The exhaust gas inlet temperature is 120°C and the outlet is at 40°C. The inlet water temperature is 35°C while the outlet water temperature is at 50°C...
  4. D

    What is the relationship between pipes and temperature?

    It seems for me that something is missing on the question. Actually, I do not know where to start.
  5. J

    Understanding a simple statement regarding the measurement of temperature

    Summary: 1.In the context of calibrating a scale to correlate volume change with temperature, my book states: "Since all substances change dimensions with temperature, an absolute reference for expansion is not available." What do they mean by an absolute reference in this instance? My...
  6. C

    Decompression of dry air in relation to temperature

    I have a problem that i cannot solve despite my best efforts. I do realize not all information here is relevant, but i still included it so you could get the full picture. Imagining we have a cylinder that is filled with dry air (normal air without water vapor) that has a fixed volume of 8,5...
  7. J

    Find the equilibrium temperature & the amount of ice/water

    That's how far I've gotten and now I'm stuck!
  8. A

    Given RMS Speed, Find Temperature

    mass of N2 = 28 * 1.67e-27 kg not sure if this is the right one - just googled it triple covalent bond N2 radii = 54e-12 m I tried to first find the rms speed: v = x/t = 50 * 54e-12 / 3 m/s Then I solved for T (in K): [50 * 54e-12 / 3]^2 * [28 * 1.67e-27] / [3 * 1.38e-23] = 9.14e-22 K
  9. PCal

    What is the enthalpy of what at 5 bars?

    This is the final question on my assignment and I'm clueless as to where I should even start as the lesson seems to give no guidance. Help would be massively appreciated!
  10. C

    For a throttling valve, why is it that temperature remains the same?

    For a throttling valve C.V analysis, I am wondering why is it known that temperature remains the same for ideal gases. I understand that using the energy balance equation, I end up with h1=h2. Pretty simple so far. By breaking down enthalpy into its components u1+P1v1 = u2+P2v2 I realized that...
  11. thebosonbreaker

    What temperature should be used for the Friedel-Crafts alkylation of benzene?

    Hello, My sources seem to contradict here - one claims that it should be carried out at room temperature, while the other suggests that heating under reflux is necessary. Could someone please clarify this for me? Many thanks.
  12. Molloy

    Thermosphere temperature paradox?

    This quote from Wikipedia says that temperatures in the Thermosphere can reach 2,500 C during the daytime but "despite the high temperature, an observer or object will experience cold temperatures". "The highly diluted gas in this layer can reach 2,500 °C (4,530 °F) during the day. Despite the...
  13. dRic2

    Resonance escape probability after a change in temperature

    Hi, I'm reading Lamarsh's book "Introduction to nuclear reactor theory" and in chapter 7 he discusses the influence of temperature on the resonance escape probability. He states that after an increase in Temperature, as a consequence of Doppler broadening, the microscopic absorption cross...
  14. T

    B Temperature regulation in Earth orbit

    If I had an object in an orbit around the Earth that I kept continually shaded from the sun, how cold would it get? Assuming the shade device was not physically connected to and was sufficiently far away from the object to not radiate any heat to it. And if I actively adjusted how much shade...
  15. Abimotek

    Automotive Honda EU generator -- which is the best oil temperature range rating?

    Please below attached which is best oil in my 4 stroke gen set Honda EU 10i, weather temperature attached in my area. I all so have two oil grades > 4T 10w-30 and Coastal Synthetic Blend 5W-30, please advice which will help the life of the gen set
  16. P

    How do we calculate the temperature of a laser-heated substance?

    P_b/P_a =0.4 I have calculated mass of the syrup which is 0.42g We know that the power of a laser before is 100mW and after is 40mW, that means that the energy absorbed by the syrup is equal to 0.6J/s. I'm not really sure what to do here, the substance through which laser is going is Maple...
  17. ChrisXenon

    Temperature and molecular Kinetic Energy

    We are told that temperature measures the average kinetic energy of the molecules or atoms in a substance, but this cannot be true. If I take a jar of water and put the jar in my car and drive it aorund, it won't get hotter, though it's kinetic energy must surely be higher. Clearly, I've got...
  18. C

    Why is air in atmospheric pressure and room temperature a gas?

    This seems like a simple thermodynamics question but I would like clarification. So the absolute critical temperature is 132.5 K (-221.17 F) and the absolute critical pressure is 3.77Mpa (546.7 psi). I understand that for temperatures above the critical point, a pure substance undergoes an...
  19. Magellanic

    Thermo: Calculating the temperature drop from gas leaving a system

    Hi PF! I have a tricky problem that I'm trying to model, and none of the typical textbook examples cover this--or they only cover it tangentially--so I was hoping to get some insight here. (Couldn't find a "Thermodynamics" section of the forums so if there's a better place to post this, please...
  20. Q

    High temperature electrical insolator that repels carbon deposits

    Is there any material/s that will handle CVI furnace temperatures (1250 C) and will either repel carbon deposits or react with it to create a compound that is not electric conductive? Trying to contain power to the heating element without shorting it to the base/ground through heating element...
  21. C

    Does temperature increase when water is boiling at 100C and pressure is increasing......?

    Does temperature increase when water is boiling at 100C in a closed system? I am picturing a scenario where I am boiling water in a pot to make pasta. However, I decide to close the pot as the water is still boiling. By doing this I am sealing away the system of study from the environment. Thus...
  22. M

    Calculate Temperature of Nitrogen Gas at 2 atm Pressure

    1. The problem statement, all variables and given/know Given: Nitrogen: 2g, it takes 820cm3 at 2 atm pressure. What is the temperature (T) of gas? Answer: 280K Homework Equations P*V = n*R*T P - pressure V - velocity n - moles? R - constant, 0.0820 ? when I use liters, atm T - temperature in...
  23. S

    Temperature profile between two parallel plates

    Homework Statement Imagine two parallel plates at distance ##L##. One of them at constant temperature ##T_H## and the other one at ##T_C##. Media between the plates is air. Find ##T## as function of distance from the plate with ##T_H## in steady state. Homework Equations Navier - Stokes Heat...
  24. coolul007

    Neutron Temp: Does It Apply to Subatomic Particles?

    Does temperature apply to subatomic particles, in particular the neutron? The question is prompted by the definition of absolute zero, being specific to atomic movement.
  25. P

    B How Do High-Speed Objects Traverse High-Temperature Gaseous Nebulas?

    Greetings, I read with interest some of the reports and studies of the "measurement" of the temperature of interstellar gases(H2, O2 etc) surrounding some gaseous nebulas(nebulae). Some reported temps. are in the thousands of degs. K. I was wondering how a solid object traveling at high speed...
  26. T

    A Stefan-Boltzmann Equation question (qualitative)

    Hi, In the Stefan-Boltzmann equation for radiation heat transfer, there exists expected parameters of any model (area, constants, etc.). However, the temperature is raised to the fourth power. Can someone explain why? I get that it could just be because it has been "experimentally observed."...
  27. Dimitris Catzis

    A Temperature of beta decay radioisotope (Sr-90)

    Hi, I want to develop a Monte Carlo simulation to determine the temperature of a beta radioisotope (Sr-90) of a given mass for my master thesis in Computational Physics. I am rookie to simulations. How much time will take to develop such a code. Thnaks a lot
  28. S

    Why is there no maximum temperature?

    Given that absolute zero is the lowest temperature possible, were all particles have zero vibration. And given that the speed of light is the highest speed any object, particle, sub atomic or not can travel. Using 2 of the most fundamental laws of physics thermodynamics and general relativity...
  29. G

    Surface temperature of a Cylindrical heated rod

    How can I calculate the surface temperature of a Cylindrical Heating rod after some time interval? There is internal heat generation in the rod and convective heat transfer to the surroundings.
  30. Alain De Vos

    Historic temperature data in New York/Greenwich on small and large time scales

    Hey, I'm interested in temperature recordings for the last 10 years but also for an estimate in the last billion years, this for hobby and fun. There are a lot of public sources but problem is many sites are torn down and others are created, so I feel very in the wild, it's like finding a tree...
  31. Grinkle

    Highest recorded temperature in a given year

    I thought this would be easy to find - but I can't find it. All the data I can find on-line is local to location. I am looking for data showing the highest recorded temperature on the planet per year over the past 30 years. Does anyone know if such data is compiled / accessible?
  32. E

    Why does Celsius temperature in degrees have +/- signs, since it's scalar?

    Why does Celsius degrees have +/- signs, since it's scalar?
  33. hnnhcmmngs

    How Does the Equation of State for a Solid Change with Temperature and Pressure?

    Homework Statement [/B] Find the equation of state of a solid that has an isobaric expansion coefficient dV/dT = 2cT - bp and an isothermal pressure-volume coefficient dV/dp = -bT (Assume the solid has a volume Vo at zero temperature and pressure. Enter a mathematical equation. Use any variable...
  34. GhostLoveScore

    Can I do something scientific with daily temperature data?

    I've been logging daily temperature and humidity data for two years now. In the end of each year I will put a graph like this Those are daily minimum and maximum temperatures. But I was wondering, if all this has any scientific value at all. I've been using WS2300 weather station for these...
  35. S

    Temperature of a bar to produce certain force on wall

    Homework Statement A brass bar and a steel bar, each 0.8 m long are at a temperature of 20oC. Each bar is placed at that temperature between rigid walls 0.8 m apart. The cross - sectional areas for the brass and steel bars are 0.005 m2 and 0.003 m2, respectively. The coefficient of linear...
  36. CrosisBH

    Mass of Ice required to achieve a certain final Temperature

    Homework Statement An insulated beaker with negligible mass contains a mass of 0.350 kg of water at a temperature of 76.5 °C. How many kilograms of ice at a temperature of − 23.9 ∘C must be dropped in the water to make the final temperature of the system 40.0 ∘C? Take the specific heat for...
  37. DLeuPel

    Does a waterfall have a higher temperature at the bottom ?

    So we have that KE= (2/3)kT , meaning that if I increase the kinetic energy of water, it will become hotter, I searched it and it says that at the bottom of the waterfall, the water is slightly hotter. Of course I imagine that when they refer to the bottom, they refer to a part of the waterfall...
  38. DLeuPel

    Temperature and the kinetic energy of everything

    Earth rotates, it also orbits the Sun, the Sun orbits the galaxies and these have they’re own velocities as well. We know that the kinetic energy is measured by its velocity, and also that kinetic energy is related with temperature. By this I mean that the movement of particles are a measure of...
  39. Arman777

    How Does Temperature Affect Particle Density and Expansion in the Universe?

    For ##m>T## we can write $$n\propto T^{3/2}\exp[{-(m-\mu)/T}].\tag{2}$$ For ##T>m## we can write ##n\propto T^{3}## where ##n## is number density of particles with mass m. We can derive this relationship by using ##n\propto a^{-3}## and we also know that ##a\propto T^{-1}##. Is there a...
  40. C

    Brittle to Ductile transition temperature of steel S450GD

    Hi guys, I'm having an issue at the minute with rolled coil steel, cracking and fracturing when being rolled into a profile. The material certs are within ISO specification, i.e. chemical composition analysis and the mechanical properties etc. The carbon equivalent may be a little high, but...
  41. T

    Spring and mass with varying force -- what is the change in temperature?

    Homework Statement A system consists of a mass m moving in one dimension and attached to a rigid wall by a spring having stiffness constant ##K##, as shown. The mass is subjected to a constant force ##F##, and is in equilibrium with the surroundings at a temperature ##T##. The partition...
  42. Baibhab Bose

    Temperature of a thin bulb filament

    In my assignment question, the length L and radius r is given and asked to find out how the Temperature of a thin bulb filament which depends on those two parameters. and the answer is r^(1/4)*L^(-1/2). I can't figure out how. Which relation is involved?
  43. A

    Free expansion process and temperature change

    Good day all! I have the following exercise One kilo-mole of air expands adiabatically from an initial state p1=1 bar, T1=340 K to a final state V2= 2V1. Compute the temperature of the final state, for the following cases: Joule expansion (gas free expansion with W12=0) My problem is with the...
  44. C

    Reducing the Temperature of the Hall-Héroult Process

    I am interested in whether it may be possible to reduce the temperature of the Hall-Héroult process for the electrolytic smelting of aluminum by using Li3AlF6 instead of cryolite (Na3AlF6) as the solvent for the aluminum oxide, and if this might be advantageous over current methods. Li3AlF6...
  45. DLeuPel

    Exploring Temperature: Understanding Particle Vibration and Absolute Zero

    The understanding that I have of temperature is that it is defined as the vibration of particles. Now, does this mean that in a vacuum where there are no particles the temperature is the absolute 0 ?
  46. S

    Dodelson Cosmology 4.8 Temperature of Nonrelativistic Matter

    Homework Statement Show that the temperature of non-relativistic matter scales as ##a^{-2}## in the absence of interactions. Start from the zero-order part of Eq. (4.68) and assume a form ##f_{dm} \propto e^{-E/T}=e^{-p^2/2mT}##. Note that his argument does not apply to electrons and protons...
  47. J

    I Legendre polynomials in boosted temperature approximation

    Hi all, In S. Weinberg's book "Cosmology", there is a derivation of the slightly modified temperature of the cosmic microwave background as seen from the Earth moving w.r.t. a frame at rest in the CMB. On Page 131 (1st printing), an approximation (Formula 2.4.7) is given in terms of Legendre...
  48. P

    Surface tension in terms of temperature and concentration of an added substance

    Hi! Here's a tricky thermodynamics problem, I hope you can help with it. 1. Homework Statement The boundary between two different materials can be divided into two different kind of phases: bulk phases and surface phases. For example, let's consider a boundary between water and air. We can...
  49. DariusP

    Why laser output power decreases with increasing temperature

    Why laser output power decreases with increasing temperature? By increasing temperature, I mean increasing temperature of the active medium. I think that thermal lensing alone should not have effect on output power? Just different focusing (focal length). What happens with energy levels in...
  50. Lukeblackhill

    Heat during the Day: Answers to Your Questions

    Hi! My question is: I understand that at noon-day it’s hotter because of the angle with which sun rays enter our atmosphere. But at the same time, I was wondering that the band of radiation responsible for heating things is infrared, and that at noon basically all bands of lower frequency than...
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