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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Le 15-02-24 11:53, clipka a écrit :
> Am 24.02.2015 um 17:31 schrieb clipka:
>> Am 19.02.2015 um 09:25 schrieb scott:
>>>> I'm building a bubble around my spaceship to protect from "drag" at
>>>> interstellar velocities. This site says that for subsonic craft a
>>>> parabola is a better shape for the nose. However, an ogive is better at
>>>> supersonic speeds.
>>>>
>>>> http://www.aerospaceweb.org/question/aerodynamics/q0151.shtml
>>>>
>>>> Which applies in outer space? Or, should I not use either and use a
>>>> teardrop shape instead?
>>>
>>> What is the speed of sound in space... I don't think any "supersonic"
>>> designs are necessary.
>>
>> In an ideal gas, the speed of sound is proportional to the square root
>> of the pressure... until relativistic effects kick in, I guess.
>
> In numbers: Speed of sound in hydrogen and helium is roughly 10^3 m/s at
> atmospheric pressure. With the pressure in outer space being lower by a
> factor of about 10^14, according to Newtonian mechanics the speed of
> sound in this medium would be about 10^7 times higher, i.e. 10^10 m/s -
> exceeding the speed of light by about 1.5 magnitudes.
>

That would be inversly proportional.

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Am 24.02.2015 um 23:04 schrieb Alain:

>>> In an ideal gas, the speed of sound is proportional to the square root
>>> of the pressure... until relativistic effects kick in, I guess.
>>
>> In numbers: Speed of sound in hydrogen and helium is roughly 10^3 m/s at
>> atmospheric pressure. With the pressure in outer space being lower by a
>> factor of about 10^14, according to Newtonian mechanics the speed of
>> sound in this medium would be about 10^7 times higher, i.e. 10^10 m/s -
>> exceeding the speed of light by about 1.5 magnitudes.
>>
>
> That would be inversly proportional.

Whoops - yes. Consider it a typo.

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