F=ma. All motions are caused/powered by forces. All forces are coexisting with matters. 

All matters are formed from atoms that are formed from oppositely charged basic building blocks/so-called particles.

The strongest attracting force is between oppositely charged building blocks in the atoms. The strongest repelling force is between the same charged building blocks in the atoms.

Atoms are formed from the solid positively charged core with negatively charged shell/crust and a floating negatively charged outer shell. 

The core attracts the outer shell and the crust repels the outer shell. The outer shell is constantly oscillating at radius direction under the two forces. The oscillation frequency is proportional to temperature.