Science Questions

Why are my windows so drafty?

Sun, 17th Jan 2010

Listen Now    Download as mp3 from the show Does farting make you weigh less?


Martin Taylor asked:

Why are my windows so drafty? My understanding of the second law of thermodynamics is that heat moves from a hot body to a cold one. So, can you explain to me why cold air is flowing into my very nice warm room through a gap in a badly fitted window? Iíve proved that cold air is moving in this direction by placing some soft tissue paper in the gap.


You're entirely correct about thermodynamics. If youíve got two stationary objects and you join them together thermally, heat will always flow from the hotter object to the colder object.  Itís actually pretty much how we define temperature. 

So whatís happening with your window is because cold air is definitely coming into your house, this situationís a bit different.  You're not touching two objects together and cold is moving into your hot house.  Whatís actually happening is that cold air is moving in to your house.  The laws of thermodynamics say nothing about where air goes, they don't disallow this.  So basically, large lumps of objects can move around as they like, not ignoring the laws of thermodynamics, but they aren't constrained by them in that way. 


Subscribe Free

Related Content


Make a comment

I can think of two explanations.

First, there is an opposing crack out of which warm air is escaping.

Second, the external pressure, created by heavier, denser cold air coupled with the effects of the wind, is greater than the internal pressure of the lighter and less dense warm air. Don_1, Wed, 13th Jan 2010

Can't the heat just be transferred to the colder body if the two gases come into contact? glovesforfoxes, Wed, 13th Jan 2010

See the whole discussion | Make a comment

Not working please enable javascript
Powered by UKfast
Genetics Society