Why use 流されていく in this sentence?


This is a sentence from Harry Potter and the Chamber of Secrets, from the
scene towards the beginning where Harry and Ron are flying the car and are
just approaching Hogwarts.  

> 車は湖のほうに流されていき、ハリーは思わず座席の端をしっかり握りしめた。

Which I would translate as:

> As the car drifted towards the lake, harry instinctively gripped the edge of
> his seat.

Why is 流されて(which I assume is passive of 流す) used here, instead of just 流れて?




Without having read any Harry Potter myself:

It is probably because the author wants to put an emphasis on the fact the the
car is being moved/flown through the air by an external power (magic?) as
opposed to moving by its own.




Without having read any Harry Potter myself:

It is probably because the author wants to put an emphasis on the fact the the
car is being moved/flown through the air by an external power (magic?) as
opposed to moving by its own.

