Cheapest Automatic Door Closer !!

This happened back in 2009, just months after joining my college as an Engineering student. I was visiting a senior in the men's hostel when I saw this creative invention. It was a mineral water bottle filled with water hanging from the top, on the backside of the door (inside the room). The weight of the bottle made the door to close every time after it was opened.

Since it was a college hostel, people will be going in and out all the time. Some super lazy lad found this technique so that he doesn't have to get up all the time just to close the door.

This was one of the most simple yet super innovative thing I have seen in my college life. I sure can say, this was far more innovative and useful than most of the final year projects.

Simple, but effective right?