Room for Bml and John Rennie

@JohnRennie OK. Some weeks ago you said that "the force is proportional to the average velocity if you go through the derivation of Stokes's law". I cannot understand how this can be done. Is it something obvious?

John Rennie

No, it isn't obvious. The derivation is quite complicated.

I did learn the derivation at university, but I forgot it long ago and don't know how it's done now.

Bml

@JohnRennie Do you know where I can find it? Can you guide me through it?

John Rennie

If you Google for Stokes law derivation or something like that you should find lots of articles explaining it.

Bml

10:52 AM

@JohnRennie OK...

John Rennie

Q: Deriving Stokes' law ($f_v=6\pi\eta Rv$) in a simple way

Is it possible to derive Stokes' law (Viscous force on a spherical body moving in a fluid $f_v=6\pi\eta Rv$) without using the "$\nabla$" operator (at least not in that form) or other theorems/laws other than Newton's law of viscosity and Newton's laws of motion? If yes, can anyone demonstrate ho...

Bml

@JohnRennie Wow, I'm impressed... The quality of PSE is unbelievable!

John Rennie

Yes, we have lots of really knowledgeable people on the site :-)

Though not me in this case as I never liked hydrodynamics and have forgotten most of what I learned about it.

Bml

@JohnRennie What is your favourite area of Physics, if I may ask?

John Rennie

General relativity.

Quantum mechanics is a close second, but I don't know that much about quantum mechanics. I am certainly not an expert on it.

When I was a scientist I studied colloid mechanics, but I got bored with it after a decade or so.

Bml

11:02 AM

@JohnRennie This is really difficult and counterintuitive. After studying special relativity on my own I tried to approach it, but I realised that it is really as abstruse as it is fascinating...

John Rennie

The maths is harder than SR, but it isn't that much harder unless you're doing really advanced GR. It's more that the ideas involved are really difficult to understand on an intuitive level.

Bml

@JohnRennie Yes, I agree. Some time ago I read a debate on the covariant or countervariant nature of force. A unanimous result has not yet been reached...

John Rennie

Defining force in GR is a bit complicated ...

I need to head off now. I have a book I want to finish.

Bye :-)

Bml

@JohnRennie About that... The derivation is awesome, but... there is no reference to average speed. Or am I just not seeing it?

@JohnRennie OK, bye! Let's see tomorrow...

next day → last day (107 days later) »

all rooms