You are flying in the air, and the air is rising ( or falling) - what is so hard to understand about that?
When you talk about thermal turbulence, where there are lots of parcels of air rising at different rates, you need a high wing loading to avoid getting bounced around. An F104 Starfighter, with 3 square feet of wing supporting 7 tons of plane, punches through turbulence easily. A Cessna with a low wing loading will bounce your fillings out, and a chopper, with higher loadings, will experience less bounce than that. Despite this, the teetering head of the chopper will make turbulence into something quite scary. Fully articulated and rigid heads cope better with turbulence.
