In a longitudinal wave, the motion of the medium is parallel to the direction of the wave. This means that the particles move left and right which in turn makes the other particles start to oscillate.
The UNIA founded by Marcus Garvey has a constitution which defines red, black, and green as the Pan-African colours: red representing the noble blood that unites all people of African ancestry, the colour black for the people, green for the rich land of Africa..
Old English blÃ¦c the color black, also ink, from noun use of black (adj.). The meaning black person, African is from 1620s (perhaps late 13c., and blackamoor is from 1540s). To be in the black (1922) is from the accounting practice of recording credits and balances in black ink.