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Oxbridge Physics Prelims Revision

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Nikking

Hmmm, why should F = ma? You've made me wonder that now!! Out the window goes quantum!
Do you never wonder why any of the stuff they teach us!!?

change to physics and philosophy u bum!

Reply 1001

Nikking

rokin blenda™

change to physics and philosophy u bum!

Hey slim! How's it going?

btw THAT'S NO WAY TO TALK TO YOUR WIFE!!!!

Reply 1002

rokin blenda™

ive just realised its taken you about 3 days to reach the amount of posts i have in 10 months :/

Reply 1003

Bezza

rokin blenda™

ive just realised its taken you about 3 days to reach the amount of posts i have in 10 months :/

but most of his have just said join audioscrobbler :rolleyes:

Reply 1004

rokin blenda™

Bezza

but most of his have just said join audioscrobbler :rolleyes:

which you should btw :biggrin:

Reply 1005

Nikking

Bezza

but most of his have just said join audioscrobbler :rolleyes:

I'll have you know, that I've been involved in deep phylisophical discussions (well I once posted) about the question mark, and I've been talking bout fit birds!!

P.S. why does this thread always turn to spam when I start talking? I honestly try talking bout physics and that. I mean ... hurm ..... ohw.

Reply 1006

~Raphael~

yeah and it was trying to be deep and philosophical that got you the warning points :p:

Reply 1007

Nikking

~Raphael~

yeah and it was trying to be deep and philosophical that got you the warning points :p:

Ha ha ha,
Nope, that was trying to smuggle a crocodile into the country disguise as a sheep.

hah! in your fac!

Rightio then :eek:

HOW IS IT that you don't have warning points yet, Raph? :confused:

Just what favours do those mods owe you? :rolleyes:

Reply 1010

Nikking

there must have been several incidents of pants dropping!!

Reply 1011

~Raphael~

I'm an angel, durrbrains!

<plus I give really good ****>

Reply 1012

rokin blenda™

i give up on quantum... im so bored/tired/lazy that i cant be bothed with it anymore

Reply 1013

LennonMcCartney

Nikking

Hmmm, why should F = ma? You've made me wonder that now!! Out the window goes quantum!
Do you never wonder why any of the stuff they teach us!!?

An accelerating charge creates an electromagnetic wave -- it's a consequence of Maxwell's equations, I think Duffin is a book which shows why.

F=ma, cos we choose what we want acceleration to be, we choose how we define F, so in fact it is all the more surprising that we choose some fairly random definitions of these quantities, and they obey some other laws which we guess. We choose what a wavefunction should be, we choose what energy means, we choose what position, momentum is, so it is surprising that it all works.

But we're not given the full beauty of it. For example, F=ma and all that is a rubbish way to analyse systems. Much better is to define the Lagrangian of a system as L=T-V, where T is the kinetic energy, V is the potential energy.

Then you say that the time integral of L along some path is S, the action, namely:

S=\int_{x_1}^{x_2}L dt

. Then you use the principle of stationary action (which is often misquoted as the principle of least action or principle of least effort) which says that the system will move from x1 to x2 so that the functional derivative of S with respect to the path is 0.

And then if you slightly redefine S, and the integral instead of taking one path from x1 to x2, to taking all paths from x1 to x2 (and also change the time-space dependence so that all variables are treated equally) you get Feynman's path integral formulation of quantum mechanics, which also works just as well as the Schrodinger formalism.

How cool is that?!

Reply 1014

RichE