Now, I understand, or at least I’m familiar with Archimedes’ Principle and buoyancy. In other words, I am aware that submerged objects experience an upward force which is equal to their weight minus the weight of the volume of the medium (or fluid) they displace. And, I suppose I could rephrase Archimedes’ Principle to something along the lines of the following: since the pressure is higher at the bottom of a submerged object than at its top (i.e. since, by definition, there is more fluid overlying the bottom than the top), there is a pressure gradient tending to thrust the object upwards.
But, regardless of how Archimedes’ Principle is formulated, I still don’t understand why it works the way it does.
Here’s a question that encapsulates my ignorance of the matter: Does a *single *helium atom rise through the atmosphere, or must there be an enclosed ensemble of helium atoms (i.e. a cell) for them to rise?
If the atoms are contained in, say, a balloon, I understand why they (and the balloon) will rise - the weight of the helium atoms in the balloon is less than the weight of the volume of air that is displaced by the balloon. That’s just Archimedes’ Principle.
On the other hand, if the helium atoms are not confined by the ‘walls’ of a balloon, they would each be ‘individual actors’; there is no cell of helium atoms, no column of air that they are displacing. In fact, when speaking of individual helium atoms, the only thing that I can think of that resembles a volume or a column, is the volume of air displaced by a single helium atom. But, if that’s correct, where does the upward thrust come from? What is pushing the (single) helium atom upwards? Could it possibly be the case that the ‘volume’ occupied by a single helium atom is greater than that occupied by the air molecules (whether nitrogen, oxygen, etc.) by which it is surrounded? So, again, my bottom line question: does a *single *helium atom rise through the air?
Thanks! (And, apologies for the long-winded way that I’ve phrased my question - in part that was to show the background I’m working with and so, perhaps, to give a clue to the more knowledgeable among us where my muddled thinking is coming from and, thus, where to set me straight.)
ETA: I neglected to mention that, empirically, single helium atoms do rise - all the way out of the atmosphere. Hence, my question is rooted in reality.