Fish scale the surface, interacting only with the riblet tips, not causing any high-veloctiy flow in the valleys. Since this high velocity flow now only interacts with the riblet-tip, which is a very small surface area, the momentum transfer which causes drag is now much lower than before, thereby effectively reducing drag. Also, this reduces the cross-stream velocity fluctuations, which aids in momentum transfer too. The rough, sandpaper-like texture of shark and ray skin, coupled with its toughness, has led it to be valued as a source of rawhide leather, called shagreen. One of the many historical applications of shark shagreen was
Jewish views of leather Jewish views of leather Leather has played an important role in Judaism and in Jewish life. Many items widely used by observant Jews are made from leather, such as: References to leather are found in the Hebrew Bible and Talmud. Leather was originally worn to protect against weather conditions. Over time, leather was slowly replaced by other resources as a source for garments. The first reference to leather is in the Book of Genesis that states that God gave man a “coat of skins”. In addition, the Patriarchs continued to wear the “coat of skins” throughout their rule. Leather constantly