Atoms are attracted to each other because A) electrons are attracted to protons because they have opposite charges
B) magnets pull them together
C) the protons are attracted to each other because they have the same charge
D) they have some energy

Consider an insulating crystal, made up of layers of atoms. what form would you expect the temperature dependence of the phonon heat capacity to approach at extremely low temperatures if the interlayer coupling is i)very strong (rigid coupling), and ii) very weak. explain.