While G and C have the same tube length, I think you wanted to ask "What happens when you buzz your lips for a note that doesn't match the length of tube?" So,

While G and C have the same tube length, I think you wanted to ask "What happens when you buzz your lips for a note that doesn't match the length of tube?" So, for example, a C and a D on a trumpet are different lengths. Basically: you don't get a note, or you get a funny sound. The trumpet doesn't resonate and it's very difficult to get your lips to buzz at the "wrong" note. Some very good players who have great lip control can bend a note up and down like this for effect. Poor amateurs like myself will often buzz not perfectly at the right tension and play slightly out of tune.