What is physics explanation for minimum sink rate airspeed? I did some research on Minimum Sink Rate, and saw much information defining it, (such as it is the speed at which the aircraft will remain in the air for the longest time, etc.) and how it is generally lower than Best Glide speed, and is generally a few knots above stall speed. There was also some information about what is used for (when you are trying to remain airborne for as long as possible after engine failure in order to deal with an emergency, or for gliders to maximize the climb effect from a thermal), 

…. But I could not find, anywhere, an analysis/explanation for how this works, from a Physics perspective, as you can easily find to explain Vx, (best angle of Climb airspeed), and Vy (best rate of climb airspeed), that explain/analyze them from a Physics perspective (Vx is speed at which you have the highest Excess Thrust, whereas Vy is the speed at which you have Maximum Excess Power). 

Also, from my limited understanding, what I did read seems to violate my basic understanding of what Min Sink Rate means, from a Physics Perspective. As I would understand it, Min Sink Rate Speed is the speed at which your rate of descent is the lowest, (you will remain airborne for the greatest amount of time). This is equivalent to the airspeed at which the aircraft is losing altitude, (Potential Energy), at the slowest possible rate. With no power on the aircraft, loss of energy (altitude) is directly related to total drag, (energy must be conserved!), and this occurs at L/Dmax.  All the complexities involved with determining Maximum Excess Power, or Maximum Excess Thrust, as are required to analyze Vx and Vy, become moot.  So although it appears to be accepted wisdom that Minimum sink is different from Best Glide, this seems to violate basic physics. They should both occur at the airspeed (AOA actually) where total Drag is minimized, i.e., at L/Dmax. Where am I going wrong?
From first principle, assuming the airplane is a point mass, no wind, small angle of attack, and thrust acts in-line with drag:

$$T-D-W\sin \gamma=m\dot{V}$$

where $T$ is thrust, $D$ is drag, $\gamma$ is angle of climb, $m$ is mass of the airplane, $W=mg$ is weight, $V$ is airspeed/forward speed (assuming no wind).

In a total power off scenario, $T=0$, and assuming steady-state, $\dot{V}=0$:

$$\sin \gamma = -\frac{D}{W}$$

The rate of climb ($\dot{z}$), which is the negative of sink rate, is related to angle of climb by: $\dot{z}=V\sin \gamma$. Therefore, we have:

$$\dot{z}=-\frac{DV}{W}=-\frac{P_R}{W}$$

Therefore, for minimum rate of descent, we would like the minimum power required ($P_R$).

Note: for minimum glide slope, it corresponds to $L/D_{max}$, but not for minimum rate of descent.