Compression in an adiabatic enclosure

[Kaushik]

TL;DR Summary

.

I found the below lines :

In an adiabatic enclosure, for instance, work is done on the system as the atoms of the compressing weight descends in an orderly way, but the effect of incoming piston is to accelerate the gas molecules to higher average speeds. Because collisions between molecules quickly randomize their direction, the orderly motion of the atoms in the weight stimulate thermal motion in the gas.

Could you please explain the above lines?

 

[Chestermiller]

This quote is trying to provide a simple mechanistic picture of what is happening in a gas that is experiencing an irreversible compression. The focus is on how the mechanical energy provided by the piston is converted into less useable internal energy of the gas. According to the description, the organized (non-random) unidirectional kinetic energy of the gas molecules in the vicinity of the piston is rapidly converted to randomly directed kinetic energy (internal energy of the gas) by means of molecular collisions.