Le 15-02-22 23:12, Mike Horvath a écrit :
> On 2/22/2015 2:28 PM, Alain wrote:
>> Le 15-02-19 03:22, scott a écrit :
>>>> The density of hydrogen atom in outer space is variable, but the
>>>> pressure is in the nano-pascal ( 10^-9 ) range, and we live in
>>>> kilohecto-pascal ( 10^5 ), so the influence of the drag is to be
>>>> corrected by at least something like a 10^-14 factor.
>>>
>>> Drag depends on velocity squared, so that would mean if your velocity
>>> was 10^7 times higher than on earth, you would experience a similar
>>> level of drag.
>>>
>>> I have no idea what "interstellar velocities are" though, 10^7 or
>>> more? :-)
>>>
>>
>> The 10^-9 range is for our spacial neigourhood, or relatively close to a
>> star. As you travel farther, it drops conciderably. Between the Sun and
>> Proxima Centaury, the vacuum around the moon looks like high pressure.
>>
>> In space, to have a drag equivalent to 100 Km/h on a road, using the
>> 10^14 factor for Earth region, you would need to travel at over 100 000
>> 000 000 000 Km/h (10^16 Km/h). That's  /way/ faster than the speed of
>> light ! (about 10^9 Km/h)
>>
>>
>>
>> Alain
>
>
> What about within nebulae?

Compared to most nebulaes, the best vacuum attained in the most advanced 
laboratories looks like medium to high presure.

So, when traveling at non-relativistic speed, you can normaly totaly 
ignore their presence.

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