system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What causes air turbulence and how does it shake a plane?
gpt
To understand that, first you must understand how planes fly at all. In short, airplanes fly by sitting on a cushion of air. If you've ever stuck your hand out of a car window while it's moving and felt it try and move around on its own, that's the same principle.

This airflow is usually quite uniform: low pressure above the wings, high pressure below them, but sometimes something happens to break up that uniformity. It could be the wake of another nearby airplane, a sudden change in barometric pressure from a storm in the making, or even just a big patch of chaotic air going whichever way right in front of the plane (otherwise called "turbulent air"). There are alot of things that can cause turbulence. 

Like rough waves for a boat, any rough patches in the air are going to affect the plane, but don't worry: we've come a long way from old-school Comets and DC3s, and modern planes are engineered to withstand all but the absolute most severe turbulence.