1. Earth gravity affects all atoms. So one of the forces acting on helium is gravity.
2. In a mixture of gases in a g-field, it is correct that density will allow an on-average height separation where the lighter atoms or molecules rise. In an environment like the ISS, gases actually will not separate by density. Around Earth though, yes, helium will rise to the exosphere as g-force contests with diffusive gas pressure force on helium atoms. G vector points to Earth, but the gas diffusion being thermodynamic, it's statistical as atoms bounce off each other, so the force is a 3 vector. That means the atoms not only rise but move around in the X and Y axes in the air. The entropy is very jjggly in that way.

As for me, my B.S. in Physics was from one of the best science schools in the US. If you have some science issue to discuss, bring it. <Are you a business major?> lol

1. Earth gravity affects all atoms. So one of the forces acting on helium is gravity.
2. In a mixture of gases in a g-field, it is correct that density will allow an on-average height separation where the lighter atoms or molecules rise. In an environment like the ISS, gases actually will not separate by density. Around Earth though, yes, helium will rise to the exosphere.

As for me, my B.S. in Physics was from one of the best science schools in the US. If you have some science issue to discuss, bring it. <Are you a business major?> lol

1. Earth gravity affects all atoms. So one of the forces acting on helium is gravity.
2. In a mixture of gases in a g-field, it is correct that density will allow an on-average height separation where the lighter atoms or molecules rise. In an environment like the ISS,

As for me, my B.S. in Physics was from one of the best science schools in the US. If you have some science issue to discuss, bring it. <Are you a business major?> Kid, you don't play in my league.