Science Projects And Inventions

Primitive padlocks have been around since medieval times, but their design left them prone to force or picking. In 1720, Swedish inventor Christopher Polhem (1661-1751) conjured up a lock that was much more resistant to the dexterous hands.of lockpickers.

Polhem was one of the most gifted mechanical engineers of his day. After studying mathematics, physics, and engineering at Uppsala University, he set up as a clock repairer. His ingenuity was soon spotted by important patrons, including King Charles XI of Sweden. Polhem went on to design many intricate devices both small (watch mechanisms) and large (industrial machinery). Perhaps his most enduring invention, however, was the padlock.

His basic design comprises an elliptical cast iron body containing a series of rotating disks. When locked, the disks fit into grooves on the shackle (the U- shaped bar on top of the padlock), preventing its release from the body. Notches on the discs can be aligned with those on the shackle by rotating the correct key, thus releasing the shackle and allowing the lock to be opened.

The Swedish inventor's device became known as the Polhem lock, or Scandinavian lock, and Polhem started a factory in Stjarnsund to produce it. The Scandinavian lock came to dominate the market. The design was later strengthened by the American locksmith Harry Soref, who founded the Master Lock Company in 1921. A modified version of this design is still in use today. For his many achievements, Polhem has been honored by appearing on the back of the 500 Swedish kroner note.