OT: Speed of light [was Re: Why not a Python compiler?]

Jeff Schwab jeff at schwabcenter.com
Tue Feb 12 00:06:05 CET 2008

Erik Max Francis wrote:
> Jeff Schwab wrote:
>> Erik Max Francis wrote:
>>> Robert Bossy wrote:
>>>> I'm pretty sure we can still hear educated people say that free fall 
>>>> speed depends on the weight of the object without realizing it's a 
>>>> double mistake.
>>> Well, you have to qualify it better than this, because what you've 
>>> stated in actually correct ... in a viscous fluid.
>> By definition, that's not free fall.
> In a technical physics context.  But he's talking about posing the 
> question to generally educated people, not physicists (since physicists 
> wouldn't make that error).  In popular parlance, "free fall" just means 
> falling freely without restraint (hence "free fall rides," "free 
> falling," etc.).  And in that context, in the Earth's atmosphere, you 
> _will_ reach a terminal speed that is dependent on your mass (among 
> other things).
> So you made precisely my point:  The average person would not follow 
> that the question was being asked was about an abstract (for people 
> stuck on the surface of the Earth) physics principle, but rather would 
> understand the question to be in a context where the supposedly-wrong 
> statement is _actually true_.

So what's the "double mistake?"  My understanding was (1) the misuse 
(ok, vernacular use) of the term "free fall," and (2) the association of 
weight with free-fall velocity ("If I tie an elephant's tail to a 
mouse's, and drop them both into free fall, will the mouse slow the 
elephant down?")

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