Why close the window and still feel the wind?

(Artwork: users.design)

People often find the wind blowing from a completely closed window, without a small gap. This seemed very strange. Actually, that is totally normal. Simple physical knowledge will help you understand this.

The air in the room was almost never completely silent. In the room there are often invisible streams of air generated by the air being heated or cold. Warming gas will expand and lighten, and if you get cold, it will reverse, shrink and become heavier. Light, hot air near the fireplace will be pushed up to the ceiling by cold air, and relatively cold air near a window or cold wall will sink near the floor.

Using a bubble, we can easily detect these air currents. Note that it is necessary to tie a heavy animal to the bubble so that it does not stick to the ceiling but can freely float in the air. Take it near the burning fireplace and release it, it will be "travel" from the invisible air, from the furnace to the ceiling, to the window and then down to the floor, and return leave the fire to continue the walk in the room.

That's why we feel the wind blowing from the window, especially at the feet, even though the door is closed.