Place the figure on the air car and push toward the end of the track.  When the car bounces off the end of the track the figure that was riding on the car will continue in it original direction and fly off and over the end of the car and air track.  You can show the action of a seat belt by using a rubber band and one of the carts with a flag.  Just put a rubber band around Homer and the flag.   

Wind up the jumping figure of choice.  Place it on the car and push it toward the end of the track.  Notice that the figure will jump up and down and still land on the car until the car bounces off the end of the air track.