My flight arrives at 9:00. Then I have to transfer to another flight departing at 9:40. The times seems really close. How large is this airport and will I have enough time to deplane at 9:00 and make my 9:40 flight?

It probably depends on your arrival and departure gates. If they're both of the same letter (say, C22 and C40), you should be fine. If you have to go from C to B, it might be tight, but you can probably still make it. The airport isn't huge.

Plenty of time to make your flight.

It is rough running through the airport.

Nashville airport is small. You will have more than enough time as long as your first segment is on schedule

As long as there's no issues, you should be able to get from one gate to another in no time. While i was waiting on my flight, I had the opportunity to walk from one end to the other, and it only took me about 7-10 minutes

Check the departure and arrival gates. As long as you arrive on tine, you should be fine.