Why do all molecules move

Dear Student,

They are always in motion if and only if the temperature of the surroundings is greater than absolute zero (0 Kelvin).The average kinetic energy is nonzero at 0 K, and thus, the molecules have the energy to "vibrate" (stretch or bend or rotate), also have the energy to move linearly in three dimension.
So by conservation of energy,if at least one molecule has energy, it can redistribute energy into other molecules and keep them moving as well.