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TIL about Tunnel Boom. Compression waves are generated in front of the high-speed train upon entering a tunnel. These compression waves subsequently coalesce into a weak shock wave so that a unpleasant sonic boom is emitted from the tunnel exit.

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14pr TIL a federal court in California ruled earlier this year that a lawsuit against Facebook can proceed. The suit claims Facebook is illegally collecting biometric data from people “tagged” in photos posted by other users.
NP86 TIL that the Packard plant in Detroit is the largest abandoned industrial facility in the world.
6EMBZ TIL the Pict people were named by the Romans. They left no writings, so we don't know what they called themselves. The word 'pict' and 'picture' have the same Latin root, meaning, 'painted.' The Romans named them for the blue woad with which they painted themselves.
wk9E TIL In July 2011, due to the American debt-ceiling crisis, Apple’s financial reserves were briefly larger than those of the US Government
e0P1D TIL Dogs can laugh. Scientists in the field of gelotology (study of laughing) have been investigating since 1960 and found dogs can articulate laughter through vocalizations and body language.