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

    Temperature & kinetic energy of particles in solid vs gas

    Consider the internal energy of a gas and solid (different materials) both at the same temperature, which material has the larger potential energy and why? Do they also both have the same kinetic energy? Finally is the definition of temperature as the average kinetic energy of the particles only...
  2. amrmohammed

    Logarithmic mean temperature difference for heat transfer

    Homework Statement [Update: just realized that the LMTD is a temperature difference, so my question was not valid] :P Calculate the logarithmic mean temperature difference (LMTD) to heat water flowing through a tube from 21 C (Ti) to 40 C (Te) if the tube has a fixed temperature of 45 C (Ts)...
  3. Liam A

    I Understanding the Polar and Equatorial Temperature Differences on Planets

    on earth, we have the poles being very cold and mostly frozen, while the equator is very warm and humid. i would like to know specifically what causes this. i know it is partially because of their exposure to the sun, but i'd like to know some of the details and factors involved. i'd also like...
  4. S

    Current in a solar cell when temperature increases?

    What happens to current in a solar cell when temperature increases? I found two sources with different information. 1) As solar panel temperature increases, its output current increases exponentially while the voltage output is reduced linearly.' 2) Whereas, this second website says short...
  5. S

    Pressure and Temperature Dependent Dynamic Air Viscosity

    Hello, I am currently working on a project which involves compressing air at high pressures and temperatures. I spent hours having a look for a pressure and temperature dependent equation for the dynamic viscosity of air but the only ones I could find were all temperature dependent only, such...
  6. J

    Calculate the temperature for this reaction to occur

    1. Homework Statement Homework Equations KE = 3/2 R/NA T The Attempt at a Solution By using the formula above, I used 2.4 x 10^-14 J as the mean translational KE , but it should be 1.2x10^-14 , why? I thought the mixture contains both deuterium nucleus and the proton? Why half KE of mixture?
  7. C

    Temperature dependence of the index of refraction of air

    The index of refraction for a gas depends on temperature, as well as pressure. What is an experiment that would determine the temperature dependence of the index of refraction of air?
  8. T

    Temperature after mixing ice and water

    Homework Statement 5 g of water at 30°C and 5 g of ice at -20°C are mixed together in a calorimeter Find the final temperature of the mixture. Water equivalent of the calorimeter is negligible,specific heat of ice=0.5 cal/g°C and latent heat of ice =80 cal/g. Homework Equations...
  9. poot lovato

    Can the temperature of an object be derived from the EM Wave

    Can the temperature of an object be derived from the EM Waves it emits? I know that everything having a temperature over absolute zero emits thermal radiations. The hotter the object gets, the higher the frequency of the wave goes. But for example if I have a hammer which emits a wave xHz...
  10. T

    I left a soda in the car and it still feels cold.

    After a cookout on Saturday, I left two cans of Coca-Cola in my bag. Around Monday morning which is almost two days later, when I left for school, the cans were still cold with moisture on it. The next day, I put another can of Coca-Cola in the car and only left it overnight to see what the...
  11. C

    Pressure and temperature -- the effects of one upon the other

    Greetings, I get that increased temperature increases pressure. But does increased pressure increase temperature. For example: 1) If I press down on a table with a heavy object, does it increase its temperature. 2) Or does the pressure of the crust and the mantle of the Earth, contribute...
  12. Doktor Mabuse

    Temperature at which pea protein is destroyed?

    I am taking a protein supplement that has far too much sodium in it. If I took the amount I need every day, I would far surpass the safe upper limit of daily sodium intake. I had the idea of dissolving the pea protein powder in water, filtering out the sodium, and then evaporating the water...
  13. G

    Inverse Square Law, Temperature Change, and Heat Source Temp

    I've been trying to wrap my head around the relationship between temperature increase of an object at a distance and temperature of a heat source. From what I've found, the temperature increase of an object from thermal radiation is affected by the inverse square law...
  14. M

    Temperature rise due to cycle test

    Hello all, I am working on a few test scripts to test the life of a hydraulic cylinder. (It is a mechanically operated cylinder and has a positive displacement) The testing will involve thousands of continuous pump and retraction operations, due to which the temperature of the piston seal and...
  15. T

    How to calculate the size of a star with just temperature

    Homework Statement This isn't a specific problem, but my professor told us that we can calculate the size of a star if we know the temperature of it. Homework Equations Stefan-Boltzmann Law, Wien's displacement law. The Attempt at a Solution With the temperature i can also get the intensity...
  16. E

    Calculating Temperature at a Distance from Heat Source

    Is there a formula or equation to find out how heated a place x meters/kilometers from a heat source will be, if we have the size of the heat source, it's shape, it's surface temperature, it's inner temperature, everything? + the distance between source of heat and the specific location is...
  17. Y

    Temperature of boiling surface

    What determines the surface temperature inside a pot of boiling water, right over the heat source? Can it go much over boiling temp if the water's just gently boiling?
  18. DevonZA

    Mean temperature of winding when current falls

    Homework Statement Homework Equations R2=R1(1+alpha(t2-t1)) The Attempt at a Solution R1=250/5=50ohms R2=250/3.91=63.94ohms R2=R1(1+alpha15degrees(t2-t1)) 63.94=50(1+1/254.5(t2-15)) t2= Now I found this online but the answers provided still don't match, 84.25 being the closest. When...
  19. MaxKang

    I Can you have a high temperature with very little heat?

    From what I know, temperature is defined to be the average kinetic energy of molecules within a system while heat is said to be the total kinetic energy of molecules. I know this might be something we can never achieve in real life but here's how my thought process went. Imagine you have a box...
  20. G

    Kelvin thermodynamics temperature scale

    The thermal efficiency of a reversible heat engine is solely a function of the temperature of the two reservoirs. η = f(θH,θC) = 1 - (QC/QH) (QC/QH) = 1 - f(θH,θC) (QC/QH) = Ψ(θH,θC) The simplest function that can be used is T1/T2 (QC/QH) = T1/T2 In order to define the Kelvin scale we assign a...
  21. r_prieto5

    Safety factor, temperature and torque

    Homework Statement https://drive.google.com/file/d/0BxPEJS0qVOpeWENSREI1RlNsNDQ/view?usp=sharing A hub is connected to a shaft with a shrink fit (pressurized oil assembly, grease removed). The material of the hub is quenched and tempered steel (ReH = 450 N/mm2) and the material of the shaft...
  22. OrangeDog

    Estimating drag using only a temperature profile

    I was reading this thread on Reddit about estimating drag using only a temperature profile. I was reading the responses, and I feel like most of them are missing something. Since this forum is more science-focused, what do you guys think...
  23. lfqm

    I Temperature in quantum systems

    Hi! These days I've been studying thermodynamics of quantum systems, and in so a very basic doubt come to me... I hope you guys can help me: When we study the usual hamiltonians of quantum mechanics (H-atom, harmonic oscillator, etc.)... Are these hamiltonians modeling the system at...
  24. T

    Why should a heat pump receive low return temperature?

    One is always told that a heat pump (heating water) should receive return water with a temperature as low as possible. I've never really understood why. My initial thought is that if the return is higher, then it's "easier" for the heat pump to heat the water up to whatever supply temperature...
  25. jfulky

    Finding Increase in Temperature for Two Rods

    Homework Statement A steel rod and an aluminum rod of equal length and diameter are placed end to end and secured so that they cannot flex. The rods are heated to the same final temperature, and the steel is found to increase in length by one-tenth of a percent. If the total length of the rods...
  26. Alfreds9

    Water evaporation, temperature, wind and heat capacity?

    Hi, I'd like to know how I'd put together, either elegantly or at least in physical terms, that surely water evaporation in a large pool of V volume and S surface is influenced by wind (increased by it as opposed to having side barriers), temperature (increased by direct sunlight as opposed to...
  27. C

    Rate body temperature increases given rate of heat transfer?

    Homework Statement Suppose you walk into a sauna that has an ambient temperature of 57.0°C. Calculate the rate of heat transfer to you by radiation given your skin temperature is 37.0°C, the emissivity of skin is 0.95, and the surface area of your body is 1.60 m2. I solved this first part and...
  28. R

    Effective annealing parameters in N-doped Zinc oxide

    Good day every one! Based on my research as you increased the temperature, the grain size become bigger and the thickness decreased, but in some paper, thickness increased. The effects of annealing temperature is almost the same to the temperature. But if you will considering doping for...
  29. TeethWhitener

    B Hawking radiation / String Hagedorn temperature?

    I was playing around with numbers and found that the equivalent temperature for Hawking radiation from a Planck mass black hole is ~5×1030 K. Later, I saw that the Hagedorn temperature for strings (where the partition function is expected to diverge) is reported to be around ~1030 K. I thought...
  30. M

    MHB Temperature coefficient

    Starting a car: the voltage drops from 12V to 7.2 V, it is 0 degrees out, and 150 amps are pulled from the car. What is the temperature coefficient of the resistor? I have NO idea how to do this. Help please!
  31. M

    MHB Tutoring for voltage, charge, terminal voltage drop , temperature coefficient.

    I have several problems regarding this/these topics. Is anyone available to tutor me right now? Thank you.
  32. Xoloti

    Train Whistle Echo: Calculating Distance & Temperature Effects

    Homework Statement a)a stationary railroad whistle is sounded. An echo is heard 4.0 seconds later by a train's engineer. If the speed of sound is 343 m/s, how far away is the reflecting surface? b) If the temperature of the air increased, how would this change your answer? Homework Equations...
  33. derekgabs

    Temperature change at a given time

    Good day to all, Hi, i would like to ask if there is a way to calculate the temperature change at a given time. I will use this as a basis for my study which is about designing an ice container and i would like to know how long does my ice last given its own temperature and the outside...
  34. G

    Wall temperature in heat exchanger

    My notes, using an example of a cold tube-side liquid cooling down a hot shell-side liquid stated that: ΔTb = TbS-TbT Mean tube-side wall temperature: TwT=TbT+(tube-side film resistance)/(total resistance) * ΔTb Mean shell-side wall temperature: TwS=TbS-(shell-side film resistance)/(total...
  35. U

    Temperature change of Water after dropping a ball into it

    Homework Statement Suppose we drop a lead ball of mass M into water of mass m from a height h and allow everything to settle down. What is the temperature change of the water? Assume that the container is well insulated. Homework Equations Potential Energy = mgh dU = mcdT where dU is the...
  36. I

    Cooling/heating temperature rate change

    Ok, so I could do an experiment on this first, but I decided to see if anyone knew beforehand. So basically my question is will different properties of the same temperature, exposed to the same temperature, cool/heat at the same rate? For example would a more viscous liquid cool as fast as...
  37. S

    Automotive Car Wheel Temp: Brake Rotor & Hub Heat Range

    Considering how hot brake rotors get under hard street and race track braking, what is the typical heat range experienced buy the actual wheel in contact with the rotor and hub?
  38. M

    Water and Ice mixture, Find original temperature of water

    Homework Statement An 8 cm3 ice cube (temperature = 0.00 °C) is dropped into a glass with 3 dL juice which results in the ice cube being melted. By doing this, the juice drops to a temperature of 3.00 °C. What was the temperature of the juice before the ice cube was added? (Treat juice as water...
  39. C

    Maintaining Water Temperature

    I have a combustion process, and have calculated the net enthalpy of my inlets and outlets. Some of the energy released by the combustion is used to heat a cooling stream, maintained at temperature 46degC. I wish to calculate the power required to maintain this cooling stream temperature: I was...
  40. kiwaho

    I Is there way to thermalize an electron to room temperature?

    At room temperature, particle energy is 0.025eV. Neutron capture reaction has big cross section when neutron is in room temperature. Theoretically, so does an electron. At 0.025eV, the electron velocity should be only 93.78km/s. Unfortunately almost no way to cool down an free electron to so...
  41. S

    The change in temperature of moist air

    Homework Statement 1 kg of moist air and 1 g condenses. What will the change in the temperature of the moist air be? Heat of Vaporization = 2.5*10^6 J/kg 2. The attempt at a solution The moist air will warm due to condensation. Heat of Vaporization=2.5*10^3 J/g Specific heat at...
  42. W

    Looking for resistivity vs. temperature lab charts

    Hi everyone, I am looking for basic elements resistivity vs. temperature laboratory measurements charts. Anyone has ideas where to look for? Regards
  43. TheSodesa

    Temperature as a function of 3 variables....

    Mod note: moved from non-HW forum section Apparently doing math homework on Physics Forums helps me think more clearly. The d-part of this question gave me a headache, and I already wrote all of this LaTeX code on the homework side of this site, so I figured I'd post it even though I solved it...
  44. B

    How to graph a linear relationship between T and v of sound?

    Homework Statement I did an experiment involving the speed of sound at different temperatures. I placed two microphones at a fixed distance apart and I measured the time taken for a sound wave to travel between the two mics. I repeated this for different temperatures. I want to make a graph for...
  45. S

    Calculate the change of temperature in terms of T

    Two Thermally insulated cylinders, A and B, of equal volume, both equipped with pistons, are connected by a valve. Initially A has its piston fully withdrawn and contains a perfect monatomic gas at temperature T, while B has its piston fully inserted, and the valve is closed. Calculate the final...
  46. N

    How to find variation of modulus of rubber with temperature?

    I want to know the what is the effect of temperature on modulus of rubber, mathematical expression will be helpful
  47. G

    Temperature increase with stirring?

    Let's say that I have a spoon and a cup of coofee, I stir it with the spoon does its temperature decrease or increase ? (There is friction force so a bit of energy should turn into heat but it's strange).
  48. RJLiberator

    Thermal Equilibrium Temperature Question Sodium and Water

    Homework Statement Expose the error: When sodium is placed in water, a violent reaction always occurs; therefore sodium and water can never be at the same temperature. Homework Equations Thermal equilibrium and temperature. Zeroth law. Isotherms. The Attempt at a Solution My Answer: The...
  49. ramzerimar

    Numerically find temperature in function of concentration....

    Homework Statement I don't even know if this is the correct forum for this question, but here we go. This exercise is from my numerical methods for engineers class, and it says the following: The coefficient of saturation of oxygen dissolved in fresh water is given by the equation: $$...
  50. Henry Stonebury

    Thermodynamics: Pressure and temperature from turbine

    Homework Statement A turbine is receiving air from a combuster inside of an aircraft engine. At the inlet of the turbine I know that T1 = 1273 K and P1 = 549 KPa, and the velocity of the air is essentially 0. The turbine is assumed to be ideal, so its efficiency is exactly 1. Also: R = 287...
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