hello all, i'm new here...an A-level student in the UK taking physics and looking to study aero eng. thats my profile atm. to topic.........obviously when a supersonic flow travels through a normal shock it reduces to subsonic, but which is the cause and which is the effect? apparently the shock forms due to combined pressure waves (from constructive interference from supersonic, sonic, and subsonic regions) forming a large wavefront. so from that, you could argue that the flow slows down and the shock forms as a result of that. rather than the shock slowing down the flow. i may be arguing semantics here. or i might be wrong.