“Flat on the Floor” opens Carnival Ride with front-porch banjos, scratchy fiddles, and watery pedal steel as Underwood soulfully belts out an empowering tune loaded with melodies catchier than cactus needles. The sentimental “All-American Girl” abounds with a soaring chorus and lyrics unraveling small-town imagery. She toughens things up with “Last Name,” a new traditional country-rocker with distorted guitars, sultry melodies, and roadhouse-friendly lyrics.