Thank you.
As it turns out, light does have momentum, and I think that is part of why I was thinking that there is some obviously minute mass associated with light, but it looks like even without mass, light still can possess momentum. But that returns me to my question, with a little twist on it now. If light has momentum, and passing through a medium reduces its velocity, then I also suppose that therefor its momentum also diminishes, but perhaps that's not necessarily the case, because it appears that the momentum of light is dependent upon its wavelength more than any mass or lack thereof, it appears that momentum for light is derived differently than it is for something with real mass.
I'm just beginning to unravel what was hidden from me in my years of physics courses in school, where teachers for some reason didn't explain very well the relationship between momentum, force, acceleration, and the conservation of momentum. It's proven very powerful for me now in understanding some concepts that I missed, through imo a bit of a deficit in teaching procedure for this subject. At least in my case.
Momentum is mathematically just mass multiplied by velocity (when dealing with things that have mass), which is close to the math of kinetic energy, which is half the mass multiplied by the velocity squared. When a massive (not large, just something with non-zero mass) object changes its velocity, it also, mathematically, changes its momentum, since its mass remains unchanged but it's velocity changes. The only way that an object can change its velocity is through the application of a force upon it, and so in a sense, momentum Is force, even though I know that force is mathematically defined as mass multiplied by acceleration, the bottom line is that a massive object that accelerates acquires momentum, and a massive object that decelerates 'sloughs off' momentum, as force, acting on its environment or upon another massive object.
So I remain confused about how light even though it has no mass, nonetheless has momentum, and I'm trying to work it all through cogently. And understanding the relationship between momentum and force has clarified some things, and has led me to wonder about now others, in this case, light.
So thank you again!