Question

imagine that you swinging backwards and forwards on a child's swing amd you are listening to music coming from a loudspeaker infront of you.Explain why the music might not sound right.

Answer 1

It is probably doppler frequency change; as you swing toward the source, pitch goes up, when swinging away, pitch goes down. Google Dopper Effect

Answer 2

I think you are looking for the words "the Doppler Effect". Look that up on Google.