SO: v2 (Second Timers)

HISTORY OF SONAR:   Sonar can be active where the sound is both sent out and received by, for example, a nuclear sub.  Or it can be passive, where only incoming signals are processed.  This is the preferred method of subs so they can’t be easily found.

HISTORY OF SONAR:   Leonardo da Vinci lived at the same time that Columbus set sail and landed in the Americas in 1692.  Leonardo da Vinci regularly put tubes in the water and used them to detect approaching vessels.

HISTORY OF SONAR:   Not much happened with sonar until the sinking of the Titanic in 1932 which began a fervent hunt for methods of using sonar to detect icebergs.

HISTORY OF SONAR:   The US entered WW2 in 1937 when German subs sank several ships including merchant ships going to England. Submarines were dangerous and needed to be detected.

HISTORY OF SONAR:   As sonar developed, on the unexpected side, really odd materials began to steal the show as sonar developed…including salt crystals and magnetite!

INFRASOUND: In WW2, the Allies used detectors to pick up on low frequencies coming from artillery fire. Infrasound also comes from avalanches, earthquakes, diesel trucks, waterfalls, the calving of glaciers, and volcanoes.

INFRASOUND: The 66 foot-wide Chelyabinsk meteor exploded over Russia in 2013. It was superheated as it entered the atmosphere. This caused the explosion. The explosion was so great that the infrasound traveled around the world several times! (Think. Read if you need to.)

INFRASOUND: Homing pigeons can skillfully orient themselves in flight using gathered data from infrasound in their path.

INFRASOUND: The American alligator male has an unusual mating behavior.  When the male seeks a female, he dips his back about 12 inches under the water and then makes powerful infrasound.  The sounds vibrate his back at a specific frequency creating an amazing dance of water above it.

INFRASOUND: The jumping water peaks that male alligators make are caused by what we call the Faraday effect. The scutes on his back measure almost exactly 1/3 the distance of the wavelength of the infrasound. The water dance happens because of the interaction of the sound it makes and its back.