system
Given the following post, respond as if you're commenting on Reddit:
human
Why do rockets fly upwards instead of sideways like a plane lifting off ?
gpt
Almost all of the work an orbital launch rocket does is flying sideways. That's the hardest part of getting to orbit, getting up to orbital speed.

But consider the problems of doing this at low altitude. Atmospheric drag. The problem of crashing into the Earth from losing altitude. Low rocket stage performance due to needing to have the exhaust at 1 atm of pressure (which limits the exhaust expansion and diminishes rocket Isp, which has an exponential impact on stage performance).

So the typical M.O. of a launch vehicle is to boost up above most of the atmosphere as quickly as possible and then begin thrusting sideways to do most of the work. This is more efficient because it reduces gravity losses (you don't have to "hover" against gravity pulling down and wanting to crash you into the ground), reduces aerodynamic drag, and improves engine Isp and stage efficiency.