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Question 120

Why is it that when I am in my dorm room with my window open and the door closed, there isn't a change in temperature and no wind comes in or blows around. But if I open the door, the room becomes cold and wind is felt throughout the room?
When the wind blows into your room, it comes to a stop and experiences a rise in pressure. This is an consequence of Bernoulli's equation, which recognizes that energy is conserved and that in a fluid, energy can exist either as kinetic energy (energy of motion), pressure energy, or gravitational potential energy. In this case, the wind's kinetic energy becomes pressure energy as it slow down in your room. As the pressure in your room rises, it prevents more air from entering, so you have high pressure but no movement inside your room. As soon as you open the door, the high-pressure air in your room accelerates toward the relatively low-pressure air in your hall. The pressure in your room drops and the wind can get in now. Soon the wind is blowing right through your room, as though you were part of a wind tunnel. If the wind is cold, you will be too.

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