Com a introducció a la unitat dels metalls mireu-vos aquests vídeos.[kml_flashembed movie="http://www.youtube.com/v/KGSiomv3bnk" width="212" height="175" wmode="transparent" /][kml_flashembed movie="http://www.youtube.com/v/LSJR5FdfAZc" width="425" height="350" wmode="transparent" /][kml_flashembed movie="http://www.youtube.com/v/AKiiSF7txs0" width="425" height="350" wmode="transparent" /][kml_flashembed movie="http://www.youtube.com/v/DI9l99f9144" width="425" height="350" wmode="transparent" /]