Ferris, yeah, a bouncing ball would probably be easier to explain than my column of smoke. But,...

cyberiot, If viewed from outside the transparant boxcar, you will associate external objects with the smoke's rise. Let's say the car is moving from left to right of you, and is moving 5 feet a minute. If a puff of smoke escapes the fire and you watch it rise for one minute...the car will have moved 5 feet...and the puff of smoke will have moved that same 5 feet...and in the same direction as the car has moved...forward. Now, to an observer *in* the car, the smoke will have only gone straight up. Same with the bouncing ball.