Doppler Effect

       To work out a mathematical relationship of the "Doppler effect", relating the pitch to the relative motion of source and observer, the Austrain Scientist Christian Johann Doppler placed trumpeters on a rail-road flat car and musicians with a sense of absolute pitch near the track. The locomotive engine pulled the flat car back and forth at different speeds for two days. The musicians on the ground "recorded" the trumpet notes as the train approached and as it reached. Doppler's equations help up.