First, let's take a look in the definition of HP
Hit Points represent a combination of physical and mental durability, the will to live, and luck. Creatures with more Hit Points are more difficult to kill. Those with fewer Hit Points are more fragile.
So, a creature can be damaged not only by physical damage, but also by removing its will to live or even its luck.
As already mentioned, damage types have no actual meaning by themselves.
Different attacks, damaging spells, and other harmful effects deal different types of damage. Damage types have no rules of their own, but other rules, such as damage resistance, rely on the types.
This means your actual question and problem is: how do I imagine/interpret force damage?, as it has no actual mechanical meaning in the game itself.
Well, the truth is: there is no actual correct way to think about it, so you can think of it as you like. You could think of magic missile not actually hitting the body, but instead the "soul" of the target, simply reducing its will to live, although not actually doing any damage to the body (as a bludgeoning damage would). You can also think it as a pseudo-bludgeoning. Imagine it as it makes more sense to you. Note that the damage type does not have to be consistent on "how you imagine" it across spells - each spell has its own way to interact and damage the enemy creature. Again, damage types by themselves don't have an exact meaning.
For your bonus, Radiant damage actually is quite explicit on how it interacts with the creature.
Radiant: Radiant damage, dealt by a cleric’s Flame Strike spell or an angel’s smiting weapon, sears the flesh like fire and overloads the spirit with power.