a person is sitting inside a train (train a). the train has not started moving yet. when that person looks out the window, they see another train (train b) . both trains are facing the same direction. if train b moves backwards, it appears to the person on train a that they are moving toward train b. if a reference point it added this can be changed. if the person can also see a pole next to the trainsm they will see that train a did not move and train b moved backwards.