2018 Tian Shan travel: Part 37

2018 Tian Shan

August-September 2018 travel to Kazakhstan reviewed in 2021

Commentary from 2021

Physics experiment with air pressure that I did while in the mountains!

Original blog post link:
Original post from 29.08.2018 is copied below.

Old but gold physics experiment

Here’s an old but gold physics experiment that anyone can do in the mountains. It’s about air pressure. This bottle I opened, almost emptied and closed at 2850 metres above sea level. Pressure there is 725 hPa, as measured by my phone. This means there’s less than ¾ of air there compared to sea level terrains – and the same air pressure is now trapped inside the bottle.

Let’s close it tightly, so no new air can come in or out of the bottle, and bring it to lower altitudes, and see what happens.

Well, here it is at 2100 metres. Pressure here is 774 hPa. As you can see, the perfectly smooth and round bottle got squeezed a little, as there’s 725 hPa trapped inside. Let’s take it all the way down to Almaty, at 900 metres.

Bottle got crushed under high pressure in the hostel – there’s still air at 725 hPa inside, but it’s now surrounded by 920 hPa pressure that you feel at 900 metres above sea level.

I wonder what would happen to the poor companion bottle if I was to take it all the way up to 3200 metres (so, it would be closed even higher up, with even less air inside) then take it with me on the plane and bring back home, which is on some 50 metres above sea level and has the average air pressure of 1010 hPa?

Now, what happens when I trap the high pressure air in the bottle, then bring it back up to low pressures high in the mountains?

Well, pretty much nothing – plastic bottles are mean to withstand much, much higher pressures. You know it with sparkling drinks. Here what happens is the same – the bottle gets very rigid, and makes a little hiss when you open it, as excess air inside escapes out.

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