The door being closed automatically!

The story starts from Korea when I was 15 years old. When I was in middle-school, one of my friend’s family owned the restaurant. I don’t know if Europeans are also familiar with the door that you have to pull from left to right to open. It was winter and restaurant had to stay warm to attract people. But when I went there to see my friend and take dinner, I found out that every single time when people come in or go out, the door was left open. It was really annoying for me and my friend. We were thinking about how to close the door automatically, because it was really tired for us to go there to close the door every single time. First, we thought about putting the poster on the door to make sure people close the door, but we found a bit easier and automatic way to close it. We just got an one bottle of water the 1.5L one. We didnt drank it all we left about 1/3 or half of it. We hung it to the door with the rope. So when people open the door the water bottle goes up and because of the gravity, the water bottle goes down again with doors closed. We just had to make sure that the door isn’t too heavy for people to open. It already has been 3,4years since I thought about that, and I am quite sure that I am not the only one who thought about it but as I was young, I was really happy that I did something with my creativity to actually fix the problems that can happen around us.