They hold molecules to make liquids or solids. They are the forces we break when we melt or boil a substance.All van der Waals forces are weak compared to ionic bonds, covalent bonds, and metallic bonds. However, there is a wide range of strength in van der Waals forces depending upon the type of molecules they are holding together. There are strongest of the van der Waals forces. There are London forces, which hold nonpolar molecules to other nonpolar molecules and are the weaker type of van der Waals forces.