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. PHstud

    Liquid to gas expansion temperature change in a tank

    Hello ! I have troube doing a calculation. Let's say we have a volume Vi in a tank at a pressure Pi. If I let my tank open, the tank's liquid will start to boil to keep the pressure Pi inside the tank. Now, at the end, I will have a volume Vf in the tank, and still a pressure Pi. But the...
  2. oversight

    How do I measure the temperature of my infrared sauna?

    Sooooo... I have a Far infrared (FIR) sauna. It has large flat 'carbon' panel heaters. They get warm to the touch and won't burn you if you touch them. My non contact infrared thermometer zapper says that they get to about 70 degrees C. They are meant to be producing lots of FIR. A regular...
  3. J

    Making a temperature controlled heating element

    I'm considering making a plastic melter / extruder for making my own 3D printer filament as opposed to buying the spools of it. The basics of the project are simple, but the hard part (for me at least) is making a heating element that has a control on it so that I can turn the heat up or down...
  4. T

    Temperature Conversions: Understanding the Use of Conversion Factors for Rates

    Why is that whenever we convert a temperature, say ##^\circ C## to ##^\circ F##, we use ##T_F = \frac{9}{5}T_C+32##, but whenever it involves a rate, say ##^\circ C/m##, we only multiply by the slope of the previously given formula? I would say it's because of the latter being a rate so...
  5. J

    Would this device(pic inside) work for boiling cold water?

    Imagine some giant glass(or other material) dome placed on top of some ocean or lake. Then pump some air out of this dome, until the water level rises a few meters under the dome. Place another dome below the first dome, and repeat the process, resulting in a little less pressure in the second...
  6. satyadangin

    How to design canal to reduce stream temperature?

    If i have atm temperature around 32 deg Celsius, volumetric flow 6000m3/h, fluid temperature inlet 47 deg Celcius. How to get minimum possible dimension for my canal if its maximum possible length is 180 m and fluid temperature outlet at least 40 deg Celcius?
  7. A

    Temperature on the outer surface of insulation

    This seems basic, but I'm stuck. Look at the attached picture. I'm trying to find the temperature on the outer surface of the insulation. Is it not possible because I do not know the rate of heat transfer? How do pipe designers know the required thickness of insulation needed to reduce to a...
  8. B

    I Humidity when T is not constant in space

    Hi all! How is humidity related to temperature in a system where temperature is constant in time but not in space? As an example: If we have humid air trapped between two parallel walls with T1 and T2 respectively, how does humidity behave along the line from one to the other wall? Is absolute...
  9. S

    A Critical temperature for bubble nucleation

    Consider that the criterion for bubble nucleation (in a field theory) is the following: $$\exp(-S_{3}/T) \gtrsim \frac{3}{4\pi} \left(\frac{H}{T}\right)^{4} \left(\frac{2\pi T}{S_{3}}\right)^{3/2},$$ where ##S_3## is the three-dimensional action of the theory and ##H## is the Hubble scale. 1...
  10. Anachronist

    Pressure and temperature of expanding humid air

    As a follow-on to this thread, which in turn followed this closed thread, I'm starting a new thread on a related real-world problem. Say I have a 2-liter plastic soda bottle filled partway with water, and pressurized. It has been sitting inverted (with the opening pointed down, and sealed) for...
  11. eigenmax

    Calculation of temperature of a current-carrying wire

    Hello, I'm working on an electron gun and I am wondering if there is a way to calculate the temperature of the hot cathode, from it's thickness, resistance, the amount of current running through it, or other relevant factors. This is part of an attempt to calculate the energy of the emittted...
  12. T

    Why is it so much easier to increase the temperature of something vs. decreasing it?

    Why is it so much easier to increase the temperature of something than it is to decrease the temperature? Why are refrigerators more complex than stoves?
  13. R

    Partition function for ideal gas for "medium" temperature

    Looking for the heat capacity of ideal gas due to rotational degrees of freedom. If the temperature of the gas is much higher than the temperature corresponding to the energy differential between states,the partition function can be written as the integral over the density of states. If the...
  14. C

    Calculate the moisture content of air

    Homework Statement (Simplified) During tests at cliffside power station, the following data was recorded from the cooling tower. A cooling tower has a 9 cell draft design, each diameter is 10m. Data D_o = 10m V_exit = 14.4 m/s T_exit(15 celsius) = 288.15K Ambient conditions : T(15 celsius) =...
  15. Cheesycheese213

    Does temperature change with depth in a fluid?

    Hi, so someone probably has already asked this, but does temperature increase or decrease with depth in a fluid? I thought it would decrease since it has more pressure but it is probably wrong, or doesn't make sense. I was confused because the ocean gets colder the deeper you go, but then does...
  16. S

    Earth Temperature Homework Solution

    Homework Statement Calculate the temperature of the Earth assuming that the Sun and the Earth are black bodies. Assume that Earth is in a steady state as far as energy balance is concerned Homework Equations ##\frac{E}{St} = \sigma T^4## - Stefan-Boltzman law The Attempt at a Solution The...
  17. T

    B What is the origin of the Gibbons-Hawking temperature?

    I recently submitted the following question to Dr. Michio Kaku on his Facebook page regarding an unfamiliar concept in his book "Parallel Universes": Dr. Kaku, In your book "Parallel Universes", pg. 301, you mention something called the Gibbons-Hawking temperature, a theoretical low...
  18. E

    Temperature of a spinning and non spinning asteroid

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  19. G

    Cooling a gas by releasing it into vacuum: Entropy?

    Hi. I just read an article where following cooling method is described. Apparently it's very common, but I don't know what it's called: A gas under pressure is released into a vacuum through a small hole. The average particle speed in this beam of gas is the same as before, but the...
  20. Emmanuel_Euler

    Dielectric Constant Vs Temperature Vs Polarity

    please explain the concept of dielectric constant in the simplest CHEMICAL terms possible. why does it decrease when the temperature increases? and why does it increase when the polarity increases? please keep it simple and brief.
  21. olgkd123

    How does compression cool water in a household water cooler?

    How does compression cool water in a household water cooler? I was reading and it says, " The water inside the water cooler is fed into a reservoir, where it is cooled using a refrigerant. A refrigerant is a cooling medium that is circulated in pipes that are located close to the reservoir in...
  22. D

    Why does stretching a rubber band increase its temperature?

    I was reading the Feynman lectures and in one of the chapters on thermodynamics it is stated that stretching a rubber band makes its temperature rise. I feel like I understand the thermodynamics of the rubber band and yet this statement is puzzling me. I believe that when you stretch a rubber...
  23. A

    Final Temperature of a Lightbulb filament

    Homework Statement When an incandescent light bulb is switched on, it can take a few moments for the filament to fully heat up and reach its equilibrium temperature. Assume the filament of a given light bulb is made of Tungsten, and also assume the potential difference across the filament is...
  24. T

    Effect of Temperature on Chemical Reaction Equilibrium

    here is the question (part I): For part I, I need some assistance, I cannot figure out how to do the question. I know eventually what to do, it's just working out the equilibrium constants I'm having trouble with. So to start, I want to work out the K values at 600K and 800K, I do this by...
  25. S

    A Dependence of entropy and temperature on Planck's constant

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  26. W

    Equipartition ceasing to apply at what temperature?

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  27. E

    Temperature in a Carnot heat engine

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  28. AHMEDbr

    Engineering Temperature compensation circuit

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  29. Adam Rabe

    Thermodynamics question: temperature between layers

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  30. R

    Thermodynamics Gas Mixture - Dew Point Temperature

    Homework Statement Only Number 1, not number 2 Homework Equations Dew Point Temperature T = Saturated Temperated at Vapor Pressure Partial Pressure = (mole fraction) x (Mixture Pressure) The Attempt at a Solution The dew point temperature is only dependent on the pressure of the water...
  31. R

    Gas Mixture - Dew Point Temperature

    Homework Statement Only Number 1, not number 2 Homework Equations Dew Point Temperature T = Saturated Temperated at Vapor Pressure Partial Pressure = (mole fraction) x (Mixture Pressure) The Attempt at a Solution The dew point temperature is only dependent on the pressure of the water...
  32. guythreepwood

    Taking the temperature of a wire

    I'm new here, and I hope I'm posting this in the right place. My colleagues and I are trying to take the temperature of a steel wire as it's heated. We're heating it by putting a current through it. The problem we're encountering is that the thermocouple we're using to take the temperature of...
  33. wasup23

    I Introducing two identical containers with different gasses

    If you have two different containers filled with two different gasses at the same temperature, would they have less pressure when connected to each other? Dalton's law states that each of the gases behave independently when it comes to pressure as they fill the space as if they were the only gas...
  34. M

    Calculate the temperature of a wire as an electrical current flows through it

    Hey, so I'm just wondering what are the formulas needed to calculate the temperature of a wire after x amount of time as an electrical current is passed through it. I know how to solve for it... I just forgot the formulas. Thanks
  35. M

    Most efficient temperature to evaporate water?

    Hello, I have a question for you guys and gals. I am working on a Desalination project and am ironing out questions about efficiency. What would be the most efficient temperature to evaporate water? 50, 100, 110 degrees? Does it make a difference, or is the energy required to evaporate a fixed...
  36. alan

    Temperature and volume fraction of a liquid mixture

    I have known the interaction parameter of a certain liquid mixture which has the phase behaviour can be described by the lattice model. , is it possible for us to know the temperature at the critical point? Besides, if we know the temperature at the critical point, can the volume fraction of...
  37. P

    Coming up with a function to model expected room temperature

    I have some cubic box with light bulbs controlled by a dimmer. The dimmer is calibrated in degrees (0-270). I need help in coming up with a function that would accurately predict what the temperature inside the box would be after say.. 5 or 10 minutes. Basically, I need to come up with a...
  38. T

    Multiphase Flow in Fluid Dynamics - Energy Coupling

    Hello, I have a general question regarding energy coupling in multi phase flow. My question comes is based on the text from this book...
  39. J

    I Mass and temperature relation in stars

    Hoping someone can help me here, I'm only a student so I'm sorry if my question is badly worded. I'm doing my maths dissertation on a binary eclipsing star and I'm trying to work out the mass of one of my stars. I know the B-V value and effective temperature, and I believe the equation I need...
  40. CFurner

    Torsional strength at high temperature

    High school student here I am designing an experiment to test the effect of temperature on the torque required to twist a piece of metal, and need some advice on where to start researching. What I need help with is A) finding a table of the torque required to twist steel when cold, and B)...
  41. P

    Heat Transfer: Finding temperature at the junction

    Homework Statement A furnace is constructed with 0.5 m of fire brick, 0.15 m of insulating brick and 0.25 m of ordinary building brick. The inside surface-temperature is 1530K and the outside surface temperature is 525K. The thermal conductivities of the fire, insulating and building bricks are...
  42. MathematicalPhysicist

    A question on absolute kelvin temperature scale.

    I was asked in an exam the following question: Q: How is the absolute Kelvin Thermodynamic temperature scale defined ? My answer is the following: A: The absolute zero kelvin thermodynamic temperature is defined as the temperature for which the entropy of the system is zero, i.e ##S|_{T=0} =...
  43. P

    Thermal Expansion: Finding common temperature (Ring/Sphere)

    Homework Statement Find the common temperature at which the inner diameter of the ring is 0.05% larger than the diameter of the sphere. Given: Lead sphere d = 5cm To = 70°C ∝ = 29x10-6/C° Steel ring d = 4.9975cm (the sphere is 0.05% larger than the inner diameter of the ring, hence this value)...
  44. Emmanuel_Euler

    Medical Oral cavity temperature vs rectal temperature

    Hello Guys How are you?? Today i was studying physiology Body temperature measurement and i saw in general and in normal conditions that the oral cavity temperature is lesser than rectal temperature but why the oral temperature is lesser than rectal temperature?? And what is the reason?
  45. S

    Is the idea of negative absolute temperature analogous to a virtual image?

    Is the idea of negative absolute temperature analogous to a virtual image in geometrical optics? I was reading this article about such a negative temperature: http://www.livescience.com/25959-atoms-colder-than-absolute-zero.html It seems to me that since temperature is defined by its...
  46. anuraag

    Temperature Coefficient of Plain Carbon Steel Gr 1000 to 1095

    Dear Experts, I am looking for the variation of magnetic permeability of the plain carbon steel wire grade 1000 to 1095 with respect to the ambient temperature ranging from -40 deg C to 200 deg C. Any leads will be appreciated. Thank you!
  47. L

    Final temperature real gas behaving ideally

    Homework Statement Please consider a mixture of oxygen (1 mole), nitrogen (4 mole), and carbon dioxide (3 mole). The mixture was heated in a well - insulated vessel with 753 kJ. Determine the final temperature if the mixture is composed of real gases behaving ideally as described by Eq. 3.48...
  48. N

    Temperature ballance, two systems

    Hi, I would like to ask you for advice with a problem, I'm working on. I have a regular shape object (glass cylinder) in which is the 100W heat source. The heat source is ind the middle of cylinder and radiates heat uniformly throughout it’s height. Heat, of course, gradually moving into...
  49. Adam Bourque

    What’s the expected heating load as a function of temperature?

    Homework Statement Excel Table gives Temperature of Month & Avg NOAAtemp for bill Homework Equations y = mx + b (Assuming) The Attempt at a Solution 1) if we take temp of month as temp, linear model y=-0.1481*temp+124.8. 2) If we take temp for days of bill as temp, y=-0.1466*temp+124.74
  50. DaynaClarke

    Gas Compression Temperature Change

    Homework Statement "One way to heat a gas is to compress it. A gas at 1.00 atm at 25.0°C is compressed to one tenth of its original volume, and it reaches 40.0 atm pressure. What is its new temperature?" So, I have: P1 = 1 V1 = 1 T1 = 25 P2 = 40 V2 = 0.1 And I'm looking for T2 The question was...
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