Power (land), religious freedom, more resources (spices), Gold, and trade.
Slaves were considered property. Their owners wanted to restrict their freedom so they wouldn't be as likely to escape.
Because it is important to know the composition of the object
Density is the ratio of the mass of a sample to the volume occupied by that mass, and expresses how much mass there is per unit volume of a given portion of matter. Density is a physical property of extreme importance in the characterization, identification and use of substances or materials.
