Intermolecular forces

Molecules can go through multiple intermolecular forces when coming in contact with the same molecule.  In general an intermolecular force are forces that act between stable molecules or between macromolecules.  These forces are forces that occur between separate covalent molecules.  The force smay be very weak or might be strong such as hydrogen bonding.  These forces hold molecules together. The different types of intermolecular forces are; London dispersion, Dipole, Dipole-Dipole, Dipole induced Dipole, Ionic bonding, and hydrogen bonding.  In this specific case CH4 is non-polar meaning the only forces acting on the molecule when it comes in contact with itself is London dispersion or also known as Van der Waal's force.

Van der Waal's force or London dispersion: This intermolecular force bonds with every two covalent molecules no matter if it is non-polar or polar. In a non-polar molecule elctrons are always moving and mobile.  At any time or instant they might find themselves towards one end of the molecule making that end temporarily negaitve and the other end temporarily positive.  At any time the electrons may have moved up to the other end now reversing the polarity of the molecule.  The force constantly changes the charge of the ends of the molecule.  This is the essence of London dispersion or Vander Der Waal's force.