Temperature Definition & Calculation - What is T?

[optics123]

Hello
I can't understand the mean of temperature in general. if it is the average of molecules kinetic energy what is the temperature of almost free space beetween Earth and sun?
what is the means of negative temperature? (behind absolute zero)
...
"what is the definition of temperature and how can be calculate in different physical situations?"

T=?

Thanks

 

[vlado_skopsko]

Yes, temperature is the average kinetic energy of the particles forming some object. Temperature relates with the internal energy of that object.
Heat is energy transfer between bodes with different temperatures. Heat can be transferred by conduction, convection and radiation.
So in vacuum is full with of electromagnetic waves, but if there is no object present, there is no one to have temperature.
I have no idea what is negative temperature.

 

[Fredrik]

Temperature is the quantity that tells you which way energy will flow when two systems are put into contact with each other. (Energy flows from the system with the higher temperature to the system with the lower temperature).

Let Ω be the number of accessible states. (This is the number of states that the system can change into from its current state). The entropy of the system is defined as the logarithm of the number of accessible states, times a constant: S=k_B log Ω. The reason for the logarithm in the definition is that if system 1 has Ω₁ accessible states and system 2 has Ω₂ accessible states, the combined system has Ω₁Ω₂ accessible states, so the entropy of the combined system is

S_{\text{tot}}=k_B\log(\Omega_1\Omega_2)=k_B\log\Omega_1+k_B\log\Omega_2=S_1+S_2

The logarithm is what makes entropy an additive quantity. The constant (which is called Boltzmann's constant) is irrelevant to what I'm saying in this post.

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Edit 2: I deleted what I wrote here, because one detail looked wrong to me, and I said it better in this old post anyway.
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Note that a system must have time to settle to an equilibrium state before the temperature is well-defined. When two systems with different temperatures are put into contact, the temperature of the combined system isn't well-defined until energy has stopped flowing from one the systems to the other.

Edit: The wikipedia article includes my definition, what vlado said, and a section on negative temperatures. http://en.wikipedia.org/wiki/Temperature

 

[brno17]

What is energy? I don't understand the true meaning of energy. I know the general but specifically what is it.

 

[mishrashubham]

What is energy? I don't understand the true meaning of energy. I know the general but specifically what is it.

If a body has the ability to do work it is said to possesses energy. Work is W=F.cosθ where W=work, F=force, s=displacement and θ= angle between the vectors. So if a body can move a certain a distance under the influence of a force it possesses energy.

 

[brno17]

If a body has the ability to do work it is said to possesses energy. Work is W=F.cosθ where W=work, F=force, s=displacement and θ= angle between the vectors. So if a body can move a certain a distance under the influence of a force it possesses energy.

Yes, these are examples of energy. But I mean what is it?

Is it power, is it mass etc.

According to your equation energy is work. So when I move I lose energy or I lost work?

Its hard to explain what I mean.

 

[Tide]

Temperature is NOT the average kinetic energy of particles making up a system. Rather, it measures the spread of velocities about the mean velocity of particles in a system much like a measure of standard deviation. For example, it is possible to have an object whose temperature is arbitrarily close to absolute zero but if we went with the "average kinetic energy" definition it would have "temperature" by virtue of its motion about the Sun, for example, or to an observer moving at arbitrary speed relative to the object. That's just not the case.

 

[mishrashubham]

Yes, these are examples of energy. But I mean what is it?

Is it power, is it mass etc.

No these are not examples of energy. Power is quantity derived from energy/work. Power=work done/energy released or absorbed per unit time.

According to your equation energy is work. So when I move I lose energy or I lost work?

Its hard to explain what I mean.

When you move, you do work and lose energy. Energy and work are very closely related. In fact they even have the same unit (joule). We could roughly say that energy is converted to work. For example, when you carry a box, and move it some distance, you would do work and for that you would use energy. If you suppose keep moving around for a week, you would at some point lose all your energy and then you would cease to do any work i.e. you cannot move the box anymore. If by some magical event you are revived and given something to eat, you would again gain energy from the food and can continue moving the box.

 

[granpa]

as i understand it kT = average energy per molecule per degree of freedom

 

[Dadface]

I think that should be kT/2 per degree of freedom.