Questions "heavy":

1 - Why the sun has heat and light ?
2 - Why is propagated "light" ?
3 - Why center of the earth is hot ?
4 - Why the electric current propagates in conductors ?
5 - Why propagation of the electric current heats the wire ?
6 - Why the electric arc Melt the metal ?
7 - Why the lightning makes fires ?
8 - Why the lightnings have thunder ?
9 - Why the friction makes heat and fire ?
10 - Why the fire expands ?
11 - Why meteorites melt in atmosphere ?
…

The common cause is the phenomenon of centripetal acceleration !
The primordial phenomenon in structuring the universe !
In this phenomenon, the polarities of the space converge towards a point, to a balance of the forces of attraction and rejection. This balance represents centripetal force as two thors orthogonally coupled. The two thors are mutually and alternatively dilated, making an oscillator.
This minimum structure of the space has matter properties and we can consider it nucleon, oscillator, or Giordano Bruno's monad. With their oscillation polarities and frequencies, the nucleons make structures and phenomena to galaxies.
If you admit this interpretation, the phenomena which did not have by now a clear explanation, now become logical.
Friction. Are interactions which amplify the centripetal forces of material structures and put into operation a multitude of "Faraday electric micro-generators", electricity with thermal and optic radiations, or even fires.
The thermal effect of electric current, is the effect of centripetal force and is full into the electric arc. Not current melts metal, but its centripetal force!
The same force which melts the core of the earth!