system
Given the following post, respond as if you're commenting on Reddit:
human
How are bugs able to fly by just moving their wings up and down? Wouldn't the down stroke just be counteracted by the upstroke?

What I mean is, when they're moving their wings down, they're pushing a certain amount of air down. But when they pull their wings up, aren't they pushing the same quantity of air back up? So no net air movement? How do they fly?
gpt
The wings don't go up and down in the exact same way.  If you've ever been swimming, you have first hand experience.  When you bring your arms forward, you do it in such a way that they have little surface area, so you push very little water forward.  When you bring your arms back, you spread your arms out, so you push back a lot more water.