system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Does an airplane naturally follow the curvature of the Earth when flying straight ahead, or does the pilot make adjustments?

Say you have a plane flying a straight path. Since the Earth is a sphere, would the plane eventually be gaining altitude? Or does Gravity force it to follow the Earth's curve?
gpt
Assuming perfectly "trimmed" flight, it would follow the curvature of the Earth. Gravity always tries to pull it towards the centre of the Earth, so to carry on "straight" would actually include a component heading "up". The atmosphere is curved, so going "up" (by going "straight" would mean a loss of lift, and it would fall back in to the curve.