The phrase "physical explanation" is correct and usable in written English.
Example sentence: The professor gave us a comprehensive physical explanation of the principles of thermodynamics.
Both approaches give a physical explanation of the phenomenon.
The physical explanation and implications of these findings are explained.
The physical explanation of this finding is given.
A physical explanation of the observed behavior is also presented.
Now there seems to be a physical explanation, scientists said.
The physical explanation for this special case is given.
A simple physical explanation of the noticed effects is proposed.
The physical explanation of this effect is presented.
Now, mind you, that's not yet to offer the physical explanation; it's just a promissory note.
Moreover, further investigations are made to provide a physical explanation for the correlation.
It also provides a precise physical explanation to the super plasticity of fine-structure metal alloys.
