What is main concept of implimentation of equations.?

[Aladin]

If we want to prove any equation. How we come to know that when and where we have to put the value of this or that formula or when and where we use this or that formula? e.g. (Derive an equation which shows that the absolute temperature is directly proportional to the average translational kinetic energy of the molecules)
-------------------------------------------------------------------------------------------------------
T = 2/3<1/2mv2>=?
As we know
PV=nRT --------- (1) (why did we use this equation for prove above?)
As we know.
n=N/NA (why we don’t put the P=F/A and volume formula)
Put in above equation (1)
PV= N/NA RT---------(2)
Where R/NA= k (k is Boltzmann constant)
Equation 2 becomes
PV=NkT
Or
P=NkT/V------------(3) (why we found “P”)
As we know.
P=2/3*N/NA<1/2mv2>-------------(4) (Why we use this equation we can also use this formula)
Comparing 3 and 4. (why we compared)
NkT/V=2/3*N/NA<1/2mv2>.
We get.
kT=2/3<1/2mv2>
or
T=2/3k<1/2mv2>
T=constant<K.E>
T Directly Proportional to <K.E>

Moreover,there are a lot of examples.

I am a college student of 1st year.
I face much difficulty in all these physics Derivations and I learn them by writing again and again. I have neither deep concepts in them nor our teachers tells us about these actual concepts. When we ask about these question that I asked you, hay told that it is just practice. Is it true?
Please explain my this question. I hope that you will solve my this great difficulty in physics.
I will be thankful to you.
Hamid Mahmood
Pakistan

 

[Aladin]

PLease someone repply me.

 

[Aladin]

PLease anyone give me answer

 

[inha]

I don't know if I'm way off here but it seems like you're neglecting the physics behind the formulas. Don't think pV equals nRT, think through what the symbol's mean. Doing some dimensional analysis has been helpful to me in those situations where I had no idea what I was actually calculating.

Regarding that specific derivation you use the ideal gas law because you're trying to find the relation between temperature and the average kinetic energy of a molecule for an ideal gas. Pressure is solved from the ideal gas law and kinetic theory to provide the relation. It's pretty straight forward but I think you're not thinking in a physical way here.

You know what laws/equations to use from the physics of the situation. You don't use kinetic theory of gases to calculate the kinetic energy of a car and so on.

 

[Aladin]

thank you very much inha but you did'nt explain properly.
Please Explain step by step.

 

[rayjohn01]

Aladin -- the so called laws of physics and hence equations come very gradually from observation with endless experiments ---- then someone tries to fit a mathematical relation ( Human logical ) to what they see . Energy (of motion ) momentum etc. are OBSERVED facts for instance what you observe in a simple collision .
You cannot expect an answer to the whole of mechanics in a few lines on a forum .
The secret is to understand a law at a time , such laws are always eventually rooted in experiment ( even if they were dreamt up to begin with i.e relativity ) .
Ray.

 

[Aladin]

thanks rayjohn.