Translational movement of a signal atom in a vaccuum?

[AtrusReNavah]

I had a thought-experiment I was pondering the other day. If you could somehow isolate a single atom inside a vacuum inside a Faraday cage, how would that atom behave in terms of translational movement?

 

[DaveC426913]

It would bounce around like a billiard ball with whatever initial energy it had.

 

[AtrusReNavah]

But there's nothing to "push" against? It's all alone and doesn't have the nearby interactions of other atoms to make its own vibrations "count" so to speak. Or at least this is my question.

(a la similar to one trying to run on ice)

 

[mrspeedybob]

It would not vibrate. It would travel in a straight line at constant velocity until it encountered the wall of the tank, then it would bounce off in a new direction and continue again in a straight line at constant velocity until it hit another wall of the tank. etc...

 

[DaveC426913]

But there's nothing to "push" against? It's all alone and doesn't have the nearby interactions of other atoms to make its own vibrations "count" so to speak. Or at least this is my question.

(a la similar to one trying to run on ice)

Objects in vacuum push do not push against anything. They move inertially in a straight line until they meet a resistance.

And the atom under observation had some amount of kinetic energy before you removed all the other atoms. It keeps that kinetic energy.

 

[AtrusReNavah]

Yes, but if its energy to "bounce" is from its initial kinetic energy when you got it in there, how does it keep bouncing? Wouldn't this energy eventually run out/not be useable for the same kind of movement?

 

[mrspeedybob]

Yes, but if its energy to "bounce" is from its initial kinetic energy when you got it in there, how does it keep bouncing? Wouldn't this energy eventually run out/not be useable for the same kind of movement?

Every time the atom bounces off the wall there is the possibility of energy transfer from the atom to the wall or from the wall to the atom. If the wall is kept at absolute zero then the atom will eventually transfer all of its energy to the wall and settle onto the floor. It not the atoms of the wall and the atom in the tank will maintain the same average temperature.

 

[DaveC426913]

Yeah. Wot he said.

 

[AtrusReNavah]

Fantastic, thanks. :)

 

[Matterwave]

Your posts seem to suggest (sorry if I misinterpreted) that you think an object needs to be constantly supplied with energy to stay in motion. This is untrue. An object in motion will stay in uniform motion unless acted on by an external force. This is Newton's first law.

 

[2milehi]

Gravity should be acting on the signal atom. The atom should bounce in perfect parabolas (and I rarely use the word perfect).

 

[mrspeedybob]

Not quite perfect. There will be variations in the strength and dirrection of the gravitational field from place to place inside the container. But since we're talking about 1 atom in a perfect vacuum we must be talking about an idealized, not realistic, senerio anyway.

 

[AtrusReNavah]

Your posts seem to suggest (sorry if I misinterpreted) that you think an object needs to be constantly supplied with energy to stay in motion. This is untrue. An object in motion will stay in uniform motion unless acted on by an external force. This is Newton's first law.

I was assuming as stated earlier that when it "bounced" some of that energy would be transferred.

Really though what I was interested in was if gravity could pull it to the bottom.

 

[DaveC426913]

I was assuming as stated earlier that when it "bounced" some of that energy would be transferred.

Really though what I was interested in was if gravity could pull it to the bottom.

It would indeed follow an arc, but you cannot discount the initial energy it had. You also cannot ignore what the walls are made of and what temperature they are at.