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The thing that all of us have experienced is about some stubborn jars! Does anyone know what's the reason?I think it might be related to air pressure but I don't know how to explain it!
Edit:
Right I was searching about the reason but I faced a new question!
https://ufile.io/6528
How does overturning the container solve the problem?!
Can anyone explain it thoroughly?
Thanks in advance

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    $\begingroup$ I think it's static friction and the adhesion of surfaces. It's easy to overcome air pressure with a screw mechanism. The issue is the complicated surface on surface interaction of the cap with the container and air pressure only contributes a little bit to that. $\endgroup$ Oct 13, 2016 at 18:07
  • $\begingroup$ You mean the reason is the friction between 2 surfaces?what about the air pressure? $\endgroup$ Oct 13, 2016 at 18:09
  • $\begingroup$ If you put a hot lquid in a jar, close it and wait for it to cool down there will be some added resistance from the vacuum but more than that it seems it would be the minute corrosion that eventually makes a jar hard to open. How often has there been a jar that you open readily and then it sits for a time and becomes difficult to open. Of course the biggest thing would be the initial effort put into closing the lid that would determine the force needed to open it or as stated already the friction between the two surfaces. $\endgroup$ Oct 13, 2016 at 18:43

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It could be a very simple thing: when something is hot, it expands.

If (since the jar was sealed) the temperature has dropped substantially or was closed at a higher altitude, the pressure will be a fair bit lower than normal atmospheric pressure, which means you have to put in more energy to be able to open it - hence making it more difficult.

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