A question on window draughts, hot days and bernoulli

In summary, the conversation discusses the conundrum of opening a window or a door to increase airflow in a room during hot weather. The person initially believed that opening the window decreased air pressure, but couldn't explain why the pressure would be less when the door was opened. It is explained that opening the window creates an area of low pressure, while opening the door evens out the pressure difference between inside and outside. This results in a steady flow of air. The solution lies in understanding the relationship between pressure, air volume, and temperature.
  • #1
cuttlefish
13
0
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
 
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  • #2
_loverIt makes sense that opening the window would decrease air pressure in the room, as this creates an area of low pressure. However, when you open the door, the difference in pressure between the inside and outside is evened out as more air enters the room, hence why the wind comes in. This also means that the airflow won't be as strong as it was before you opened the door, but the steady flow will remain. It's just a matter of understanding the relationship between pressure, air volume, and temperature. Hope that helps!
 
  • #3


Hello cuttlefish,

Your intuition is not leading you astray. Your observations are actually related to the principles of fluid dynamics, specifically the Bernoulli's principle.

Hot air rises and cool air sinks. When you open your window, the hot air inside your room will try to escape through the window due to the difference in temperature between the inside and outside. This creates a low-pressure area near the window, causing air to flow into the room from other areas.

However, when you open your door, the air has a larger opening to escape through, resulting in a larger decrease in pressure inside the room. This larger decrease in pressure causes a stronger flow of air into the room, creating the "puff" of wind you mentioned.

This phenomenon is known as the Bernoulli's principle, which states that as the velocity of a fluid (in this case, air) increases, the pressure decreases. This is because the faster-moving air molecules exert less pressure on their surroundings.

So, in conclusion, your observations are a result of the Bernoulli's principle and the natural behavior of hot and cool air. I hope this helps alleviate your curiosity. Keep observing and questioning, as that is the essence of science.
 

1. What causes window draughts?

Window draughts are caused by a difference in air pressure between the inside and outside of a building. This can be due to various factors such as wind, temperature differences, and improper sealing around the window.

2. How can window draughts be prevented?

Window draughts can be prevented by properly sealing any gaps or cracks around the window frame. This can be done using weather stripping or caulking. Installing double-glazed windows can also help reduce draughts.

3. Why do hot days make window draughts more noticeable?

Hot days can make window draughts more noticeable because warm air rises and creates a pressure difference between the inside and outside of the building. This can cause the draughts to feel stronger and more uncomfortable.

4. What is the Bernoulli principle and how does it relate to window draughts?

The Bernoulli principle states that as the speed of a fluid (such as air) increases, its pressure decreases. This principle is related to window draughts because as wind or air flows over the outside of a building, it creates an area of low pressure, which can pull air out of the building through any small cracks or gaps, causing draughts.

5. Can window draughts affect energy efficiency?

Yes, window draughts can significantly impact energy efficiency in a building. They can cause heated or cooled air to escape, leading to higher energy bills. Properly sealing windows and reducing draughts can improve energy efficiency and save money in the long run.

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