system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do tractor trailer trucks need help to extricate themselves when they are jackknifed? Why can't they just turn their wheels and straighten out on their own?
gpt
The wheels on the trailer aren't powered. This isn't a problem when the truck is pulling them in a direction mostly parallel to the direction the wheels move, but the further the trailer turns the less of the force the truck produces is pointed in that direction. If the truck is pulling perpendicularly to the direction of the wheels, zero force is being applied in a direction the trailer can actually move, and so it won't. At that point no amount of turning the wheels on the truck will move it, as all the force the truck produces will be applied to the hitch, in the direction the truck is currently facing.