How can a cloud generate lighting and thunder?

Question

I mean its just a bunch of water and air

Answer 1

Warm and moist air rises into the sky and cools dramatically forming thunder clouds.Some of the water inside the clouds freezes and strong air currents make the ice and water droplets bump together.This knocks tiny charged particles called electrons from the ice and there is a build-up of electrical charge.
In this process, some clouds lose electrons and acquire positive charge and others collect those elctrons and become negatively charged.
When clouds holding positive and negative static electrical charges approach one another,they constitute to form capacitors.Just like a capacitor discharges its accumulated charge once the breakdown potential is reached,the clouds(or a cloud and ground) also discharge the charges once the potential difference exceeds a certain limit.
This charge is released by a stroke of lightning and thunder in the following manner:-
During the course of the discharge, a very heavy current flows between the clouds( or between the cloud and the earth) and this electrical energy is converted into enormous heat which heats the air to an incredible 30000 degree celcius or 54000 degree fahrenheit, five times hotter than the surface of the sun.This heat devastates molecules and particles of the discharged portions of the clouds into a plasma state which emits bright radiation(lightning light) and sends intense pressure variations in the atmosphere resulting in the sudden expansion of air faster than the speed of sound.It is this which produces a loud noise called thunder.

Answer 2

Basically clouds generate the static electricity that's needed for a bolt of lightning the same way you build up static electricity by scuffling your feet over a carpet....friction. Within thunderstorm clouds there's a great deal of turbulence which causes air molecules to rub together.