system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does travelling, even when it is essentially sitting still, tire you more than sitting still in a stationary place?
gpt
When sitting stationary your body exerts effort just to keep you upright in your seat. 

When sitting while traveling, your body exerts effort to counter every motion of the vehicle you happen to be in. Vehicle slows down, your core muscles react to keep you pressed back into your seat, and you don’t recognize this as anything more than still sitting down. Same for every turn, your core reacts to counter the centripetal motion to one side or the other. 

So sitting while traveling gives you an unconscious core workout that you never recognize.