Is spave really a vacuum???

[holocene]

Standard atmospheric on Earth is around 14.7psi. This is positive pressure.<br /><br />Travel out of that atmosphere and into space, and the pressure should be zero, no?<br /><br />Even if the pressure is zero, that's not a "vacuum".<br /><br />Vacuum is a <i>negative</i> pressure, and zero is not negative.

 

[yevaud]

A vacuum is defined as an absence of atmosphere. True, there are a few molecules here and there out in space.<br /><br />You see, it's all <i>relative</i>. A vacuum can be defined as a steep negative pressure gradient with respect to some other source. Answer.com provides one of the meanings: <i>space in which the pressure is significantly lower than atmospheric pressure.</i><br /><br />That help? <div class="Discussion_UserSignature"> <p><em>Differential Diagnosis:  </em>"<strong><em>I am both amused and annoyed that you think I should be less stubborn than you are</em></strong>."<br /> </p> </div>

 

[holocene]

Thanks. I just think the term "vacuum" is a bit misleading...

 

[bobw]

There are two basic ways to measure pressure; gauge pressure and absolute pressure. You can use torr or bar or inches of water, etc. for your units but they are all relative to a reference point.<br /><br />With gauge pressure the reference point is atomospheric pressure so if you pull the gauge out of the box it will read zero. You are right about negative pressure with that kind of gauge. If you pull a vacuum on your container your gauge will read negative pressure. If you pull a total vacuum on your container the difference between the inside and outside of the container will be about 15 psi so your gauge will read -15 psi. Once you get all the air sucked out you can't suck out any more so your gauge can't read more than -15 psi unless you pressurize the outside of the container.<br /><br />Once you have sucked all the air out of the container; if you are using an absolute pressure gauge it will read zero. If you have a new absolute pressure gauge and take it out of the box it will read 15 psi not zero like the gauge pressure gauge did.<br /><br />Outer space doesn't have many molecules so it is pretty close to a total vacuum. Your gauge pressure gauge will read -15 psi but your absolute pressure gauge will read zero.<br /><br />I hope that helps. It depends on what kind of gauge you use. <div class="Discussion_UserSignature"> </div>

 

[holmec]

>Thanks. I just think the term "vacuum" is a bit misleading...<<br /><br />Blame it on Hoover. <div class="Discussion_UserSignature"> <p> </p><p><font color="#0000ff"><em>"SCE to AUX" - John Aaron, curiosity pays off</em></font></p> </div>

 

[keermalec]

I would say spave is not really a vacuum, but almost. Lowest observed density in the Galaxy is 1 hydrogen atom every 16 cubic centimetres, whereas at sea level you have about 10E27 molecules per cubic meter of air... <div class="Discussion_UserSignature"> <p><em>“An error does not become a mistake until you refuse to correct it.” John F. Kennedy</em></p> </div>

 

[docm]

Even in the absence of "real" particles you have a huge flux of virtual particles popping in/out of existence at every level of measurement, not to mention those particles that are nearly impossible to detect like axions etc. etc. <div class="Discussion_UserSignature"> </div>

 

[weeman]

Vacuum can certainly be misleading when you're applying it to the nature of Space. However, it can be used as a very general term to describe that space has no atmosphere, and therefore no pressure.<br /><br />To many people on this board we might look into the term "vacuum" more scientifically, and say that it is misleading. But to the average person, the term vacuum explains plenty. <div class="Discussion_UserSignature"> <p> </p><p><strong><font color="#ff0000">Techies: We do it in the dark. </font></strong></p><p><font color="#0000ff"><strong>"Put your hand on a stove for a minute and it seems like an hour. Sit with that special girl for an hour and it seems like a minute. That's relativity.</strong><strong>" -Albert Einstein </strong></font></p> </div>