A question on window breezes and bernoulli effect

[cuttlefish]

Hello there!
It's been about a grillion degrees up here in my home town recently and last night this led me to a sort of conundrum. If I open the window in my room but leave my door shut, hardly any air comes it at all. If I open my door, there's a strong puff of wind that comes into the room and then a good steady flow continues. Just because of the components of this situation I always assumed that it had something to do with air pressure. Somehow opening the window decreased the air pressure in the room, sucking in cool air from the outside. But I realized that I can't really explain why the pressure would be less once you opened the door. Is my intuition just completely leading me astray? I've been thinking about this all night, somebody put me out of my misery!
cuttlefish

 

[RTW69]

Your house is a big box of stratified hot air warmer than the out side air because of heat from lights, appliances etc. If your house is air tight an open widow will not let outside air into the house because there is no way for the air in the house to excape. However if you put a hole in the top of your house (gaps around windows, exhaust fans, plumbing penatrations etc.) the warm air in the house will excape and be replaced by relatively cooler outside air. The leaks around the top of the house creates what is called a "stack effect" similar to that of a chimney. The effect can be increased by increasing the temperature difference between inside and outside air, increasing the height of the house or wind driven affects. The fact that you have air entering a house tells you that air must be leaving somewhere else. The air movement will be caused by pressure differences created by the stack effect.

 

[astrokreng]

Hello there, cuttlefish! Your intuition is actually correct - the difference in air pressure is indeed responsible for the difference in air flow when you open the window and the door. This phenomenon is known as the Bernoulli effect, named after the Swiss mathematician Daniel Bernoulli who first described it in the 18th century.

In simple terms, the Bernoulli effect states that when the speed of a fluid (such as air) increases, its pressure decreases. When you open the window, the air outside is moving faster than the air inside your room, creating a lower pressure outside. This lower pressure then causes air from outside to flow into your room through the window.

When you open the door, the air inside your room can now flow freely into the rest of your house, creating a larger volume of air moving at a higher speed. This results in a lower pressure inside your room, causing air to flow in from the window even more strongly.

So, your observation of a stronger breeze when the door is open is due to the combination of the Bernoulli effect and the increase in air flow through the larger opening. I hope this helps to put your mind at ease! Stay cool during those hot summer days.