Re: [ros-dev] Very nice.

[Jose Catena]

I also think it may be not a good idea to discuss physics here. But since
this is going on anyway, I think I may help to find an agreement and end
this. Please forgive me and skip the rest of this post if you aren't
interested.
I think everyone participating in the discussion knew what the centrifugal
force is, and all the confusion could be explained by assumptions on what
the 'real' definition is, since the natural language adjective is ambiguous
as a scientific definition. Perhaps this happened with more than one word.
It is not important if we name a force 'real' or 'abstract', as long as
we
understand what it actually is and agree on definition of 'real', what is
not obvious as proven in the discussion.
Forces are vectors (forget for now that 'vector' is in itself an
abstraction). For analysis, many times natural forces are expressed as sum
of vectors. Of course this makes another abstraction, every time we apply
math we are abstracting in some way. Although it is also a valid meaning of
'real' something that can be demonstrated mathematically.
Instead of centrifugal force, I'll put an example that I think is pretty
useful to show the conflict: the force the air causes to a wing moving on
it. The 'real' or single force vector is not useful for understanding or
analysis, so we always express it as a sum of two vectors: 'lift' and
'drag'. I never hear of anyone saying that these are not real since their
effect is demonstrable, while most people would consider the single natural
force an abstraction, since it is demonstrated and understood as the sum of
the two calculable components lift and drag.
Furthermore, we often consider how a sum of forces are applied to an object,
while at the end, only the sum is what matters to the effect produced, and
in this case we might say this sum is an abstraction while the components
are 'real' or not (they may be also abstracted components of a real
force)...
You see how assuming the meaning of words may be so confusing in science.
As I see it, the problem in the discussion can be solved by delimiting the
meaning of 'real', or much better, avoiding this ambiguous adjective in
favor of a more explicit one. Indeed the centrifugal force is not directly
caused in the nature, so if we say 'real' means a direct representation of
something that physically exist, it is not 'real'. But we may also say that
'real' means it can be demonstrated mathematically, and then the centrifugal
force is certainly 'real', as would 'lift' and 'drag' in a wing.
Both are
valid meanings of 'real' in different scopes (physical existence vs.
scientifically demonstrable).
Something that unfortunately happens too often. In any kind of discussion,
people should try to understand each other's reasoning instead of
nit-picking on definitions to discredit them. It is different than an
exhaustive essay where the author should be careful to clear any ambiguity.
We couldn't speak if we had to be scientifically accurate in every word.
Sorry for the long and off topic post, I advised to skip it if no
interest... ;-)

Jose Catena
DIGIWAVES S.L.