Joat42 wrote:Loren Pechtel wrote:You're looking at the macro level. At the micro level those molecules are averaging 500m/s. That's faster than most handgun rounds.
Sigh....
In a best case scenario at 1 atmosphere and at room temperature, excluding all other external factors, an air-molecule moves about 1cm/s on average. The 500m/s number is the speed it moves in a straight line until it runs into another molecule and bounces off in a new direction - ie a random walk in 3 dimensions and taking that into account we get the number I mentioned above.
The number I used can be calculated by using the size of an air-molecule, it's speed and the amount of other air-molecules present in a fixed volume with the assumption that they are fairly equidistant from each other.
Loren Pechtel wrote:But there's nothing to bump into in the vacuum you're trying to create next to the backstop. Thus the 500 m/s number is the relevant one, not the 1 cm/sec.
That isn't really relevant. If we examine a random molecule it'll have a direction that is also random, but as long it's moving towards the field it'll be sucked out. In an ideal case (enclosing walls/fields are of equal area) the number of molecules moving in the direction (at whatever angle) of the field for a given moment will always be 1/6 of all molecules within that space. The molecules will "bounce" off every wall except the one consisting of a gravity field pointing away from the enclosed space. Think of the gravity field as a variant of Maxwell's demon that moves molecules from one space to another.
If it were otherwise, even an mechanical vacuum pump wouldn't function.