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. 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...
  2. 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...
  3. 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.
  4. P

    B Temperature of 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...
  5. 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."...
  6. 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
  7. 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...
  8. 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.
  9. 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...
  10. 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?
  11. E

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

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

    Equation of state of a solid

    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...
  13. 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...
  14. 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...
  15. 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...
  16. 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...
  17. 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...
  18. 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...
  19. 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...
  20. 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...
  21. 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?
  22. 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...
  23. 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...
  24. 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 ?
  25. 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...
  26. 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...
  27. 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...
  28. 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...
  29. 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...
  30. Chromatic_Universe

    A Equilibrium recombination temperature for Helium

    How to get to the expression for equilibrium recombination temperature for Helium?
  31. R

    What is the final temperature of the air in a tube

    Homework Statement I have a copper tube with outer radius r2 and inner radius of r1. Half the tube is exposed to the surrounding air while the other half is embedded into the ground. The outside air temperature is T2 and the ground temperature is T3. What is the air temperature inside the tube...
  32. Edge5

    The thermal speed of an electron at room temperature

    I am trying to find the thermal speed of electron at room temperature. kT = (1/2)mv^2 which gives v=√((2kT)/m) but answer says it should be √((kT)/m) Where did that 2 go?
  33. H

    Probability at a temperature T that a system has a particular energy

    Salutations, I'm starting in statistical mechanics and reviewing some related studying cases I would like to understand what occurs in small systems with normal modes of vibration, for example, a small system that has 2 normal modes of vibration, with natural frequencies $$\omega_1$$ and...
  34. dwight_v

    Final temperature for two blocks of iron placed in contact

    Homework Statement Two blocks of iron, one of mass m at 10.0C and the other of mass 2m at 25.0c, are placed in contact with each other. If no heat is exchanged with the surroundings, which of the following is the final temperature of the two blocks? A)10 B)15 . D) 20C ( this is the answer) The...
  35. DracoMalfoy

    Power and temperature of stars

    Homework Statement Star 1 emits energy at a rate that is 2 times that of Star 2. If Star 1 also has a radius that is 3 times larger than Star 2, how do the temperatures of the stars compare? a. Star 1's temperature is 2.58 that of Star 2. b. Star 1's temperature is 3.75 that of Star 2. c...
  36. B

    Temperature Measurement: Are All Thermometers Created Equal?

    What is the difference in temperature with different thermometers for the same object? Thanks !
  37. T

    Mean Rating Temperature for insulation in ASHRAE

    Hello, Can someone please tell me what the mean rating temperature in the tables provided in ASHRAE fundamentals, ASHRAE standard 90.1&90.2 for chilled water insulation indicates.
  38. A

    What is the correct way to find the temperature of helium in this scenario?

    Homework Statement Helium is kept in a pressure vessel at a pressure of 5.42 bar and the resulting density is 0.92 kg/m3. The gas constant R is 8.314 J/(mol*K). The volume of the vessel is 1589.194 m3. I need to find the temperature of helium in Celsius. Homework Equations...
  39. Graeme M

    B What does it mean to say that "space" has a temperature?

    I was thinking about the fact that space contains all sorts of matter and that these objects have temperatures. But then I read that space itself has a temperature depending on where you are. The cosmic background radiation for example has a temperature of 2.7K. Can someone explain what that...
  40. bbbl67

    I Calculating the Sun's core temperature?

    Knowing the following information: Sun surface temperature of 5788 K, Sun's core is between 20-25% of radius. I tried to (perhaps naively) calculate the temperature to the edge of its core from the surface temperature, using an inverse square law. Depending on which value you use for the core...
  41. P

    Black Hole Temp: Calculate Specific Heat

    Homework Statement Compute the specific heat of black hole Homework Equations ##T=\frac{2}{r_+}-3/2048 r_+^2-\frac{6r_+^3M^2}{(M+r_+^6)^2}## ##f(r)=1-\Big (\frac{r^2}{64}+\frac{Mr^4}{M+r^6} \Big ) ^{1/2}## ##r_+## is the horizon where ##f(r=r_+)=0##. The Attempt at a Solution I tried to...
  42. YMMMA

    PV diagram/ which labeled process has no temperature?

    Homework Statement I have had a question in my quiz that I don’t remember very well, but here’s a diagram and there’s no need for numbers in axis because it’s a concept- based question with no calculations. The question asks if an ideal gas system moved from A-B-C-A. Where is the process by...
  43. O

    Liquid temperature increases when flowing through a 100% efficient pump?

    Hi, For an ideal Rankine cycle, the temperature-specific entropy diagram can be given as follows, The pump in this cycle is isentropically 100% efficient. My question is that why the temperature of the water increases as it flows through the pump (point 1 to 2) if the pump is 100%...
  44. A

    How to calculate the refractory wall temperature?

    Homework Statement A gas-fired tube heater has the following data: Dimensions of the combustion chamber: 15 * 20 * 40 ft Tube outside diameter: 5 in Temperature of the tube=800° F Center to center spacing: 8 in Number of tubes (arranged in a single row of which 6 tubes are shield tubes) ...
  45. R

    Temperature profiles and thermal resistance

    I heated two different materials with a laser beam for about 10 seconds and these are the measured temperature profiles: From the various solutions to the general heat conduction equation, temperature rise seems to increase with increasing thermal resistance of the material. The total...
  46. Krushnaraj Pandya

    Brightness change with temperature

    Homework Statement A black and yellow body at room temperature are thrown into a furnace at very high temperature. How will the initial and final brightness of both compare? Homework Equations λT=constant The Attempt at a Solution The rise in the black body's temperature will be higher...
  47. Krushnaraj Pandya

    Change in radiation with temperature

    Homework Statement What would be the increment in heat energy radiated when the temperature of a hot body is raised by 5%? Homework Equations P=σεAT^4 The Attempt at a Solution dP/P=4dT/T dT=5 when T is 100 initially. Let's assume P was also 100 initially for convenience, therefore dP should...
  48. Krushnaraj Pandya

    Heat capacity and temperature problem

    Homework Statement A piece of metal is heated by supplying a constant power P. The temperature of the metal starts varying as T=kt. The heat capacity of the metal as a function of temperature is? Homework Equations Q=CdT The Attempt at a Solution From Q=CdT, dT is k, since P is Q/t, I plugged...
  49. J

    Calculate the final temperature of the mixture

    Homework Statement Consider the following reaction. 2 HCl(aq) + Ba(OH)2(aq) BaCl2(aq) + 2 H2O(l) ΔH = -118 kJ Calculate the heat when 100.8 mL of 0.500 M HCl is mixed with 300.0 mL of 0.450 M Ba(OH)2. Assuming that the temperature of both solutions was initially 25.0°C and that the final...
  50. J

    Calculate the final temperature of the solution

    Homework Statement Consider the dissolution of CaCl2. CaCl2(s) Ca2+(aq) + 2 Cl-(aq) ΔH = -81.5 kJ A 10.6-g sample of CaCl2 is dissolved in 109 g of water, with both substances at 25.0°C. Calculate the final temperature of the solution assuming no heat lost to the surroundings and assuming...
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