Home-made barometer

2 06 2014

This weekend a friend of mine asked me if I wanted to walk up Ben Nevis.

I’m not much of a walker, in fact most people that know me thought mountain rescue would be involved at some point, but I had a new science experiment and this was the perfect opportunity to try it out.

I’ve seen a few people on the Internet use plastic bottles to show the differences in air pressure at different altitudes. The sealed bottles crumple or expand depending on whether they are brought up or down a mountain. That’s fine if you’ve got a huge mountain to go up and down but what about if you wanted to try it in the UK? I wondered if there was a way to do it to show a more sensitive difference.

This is my contraption. It’s a balloon inflated inside a bottle so if you’re looking down into the bottle you also looking down into the inflated balloon.

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This is a view looking down into the bottle and the balloon. The balloon is inflated but the top hasn’t been tied, it has been folded over the open end of the bottle (and helped to stay in place with a cable tie).

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At sea level in Fort William the balloon in the bottle took up this much space.

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At the top of Ben Nevis, 1344 m, the balloon took up this much space in the bottle.

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I only thought to measure the difference in how much space the balloon took up using tape and as you can see from the pictures it was a pretty rough effort.

Just as we were returning back to the car park (6 hours later) I thought I should have filled the balloon with water at the top and the bottom and used a measuring jug to see how much volume was inside the balloon.

Let me know in the comments if you think that would have worked.

Given how stiff my knees are two days later unfortunately there won’t be a follow-up experiment any time soon, and to be honest, I don’t think We could have found a better day to do it anyway.

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I won’t tell you now how I managed to inflate the balloon inside the glass bottle, there is a hint if you have a look in the bottle. It’s a combination of the squeezing an egg into a bottle and the collapsing can demos.

According to my research the air pressure at the top of Ben Nevis should be 86% of the air pressure at sea level given a constant temperature. For the record it was about 20°C at sea level and 7°C at the top.

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