I was reading this answer by madame anna v:
You are right, the planetary model of the atom does not make sense when one considers the electromagnetic forces involved. The electron in an orbit is accelerating continuously and would thus radiate away its energy and fall into the nucleus.
One of the reasons for "inventing" quantum mechanics was exactly this conundrum.
The Bohr model was proposed to solve this, by stipulating that the orbits were closed and quantized and no energy could be lost while the electron was in orbit, thus creating the stability of the atom necessary to form solids and liquids. It also explained the lines observed in the spectra from excited atoms as transitions between orbits.
But I don't understand one assumption: Why would an electron in an orbit be accelerating continuously, and would thus radiate away its energy and fall into the nucleus in a classical model?
Also in a planetary model, would planets also be accelerating and thus fall into the sun?
I mean for example: a planet would accelerate towards the sun, but because it will then have bigger velocity, it will escape a little bit the sun, and then it will accelerate towards the sun... and the whole process repeats again. But, why wouldn't that be true for an electron and proton?