2. (a) Describe crystal and amorphous structures. (b) Polymers can have a crystalline or an amorphous structure. Identify one engineering application suited to a crystalline polymer and one suited to an amorphous polymer. Relate the differences in material properties of crystalline and amorphous polymers to the two applications. (c) Explain the following crystal structures, using a clear diagram/illustration for each: body-centred cubic, face-centred cubic, hexagonal close-packed. (d) Explain the meaning of coordination number and packing fraction, referring to the three structures listed.