While traveling within the united staes do you need a passport to travel by air.. say to go from Tennessee to NY?

No you don't need a passport if you are a US citizen. It is good, however, to have valid picture I.D. though. If you are a foreigner in this country I would suggest taking along your passport for identification reasons. Since 9-11 the airport security people can get pretty hinky and this will speed you along and you should not have any delays at the airport.