human
Why do the trains go round in circles on the model railway?
assistant
Well, it’s a model railway, so it’s not a real railway. It’s a toy train. Trains on a model railway are powered by electricity. The power is supplied to the train through a special kind of track called the “third rail” which is located along the track. The train’s wheels make contact with the third rail, which causes the train to move. When the train reaches the end of the track, it reverses direction and goes back to the beginning of the track.