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..
Ethiopians are proud of the fact that they have never been conquered throughout their history. Africans adopted the Ethiopian tri-colours, green, gold and red, as theirs. It eventually became the colours of pan-Africanism. Yet as can be found on the internet, there are some who find that fact a bitter pill to swallow.