Falling Whistles
Falling Whistles sells whistles for $34 to $104 to raise money for education, advocacy, and the rehabilitation of war-affected people in Congo. The organization got its name from a journal written by its founder, sharing his experiences during a trip to eastern Congo in 2008. During that trip, Falling Whistles' founder met a group of five former child soldiers who told him that some children who were too young to carry weapons were sent into battle armed only with whistles. By wearing whistles, the campaign aims to use this weapon as a tool of protest and to raise awareness of the situation in Congo. As of September 2010, $500,000 has been raised.
Physics of whistles
The yellow plastic pipe is actually a child’s toy that sounds when the pipe is whirled around. The metal pipe shown was used in the Concorde cockpit to provide cooling air to the pilots, but its loud tone got it canceled. This whistle is similar in many respects to the hole tone, in particular the teapot whistle. It is subject to frequency jumps and hysteresis loops. There are numerous articles on the internet about this whistle and it has been studied.