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# Phun with Phyphox....

I downloaded Phyphox over lockdown and dipped in and out of it a few times over the last two years, but I was always aware that I wasn't making full use of it - so I was delighted when Paul Nugent and David Keenahan of the IoP ran a workshop on it during the ISYA conference at the beginning of the Easter holidays.

They left me with a great set of easy-to-perform experiments that I've been working my way through ever since. I've measured the speed of sound and the height of a bouncing ball using the acoustic stopwatch, and today I measured the height of the hill shown below using the pressure sensor.

The hill sits just behind my lab. It's believed to be the burial mound of Cumhal - father of Finn MacCumhal - who apparently died in a battle on the site, though I don't think its ever been excavated. Today its occasionally home to a herd of cattle and is also the site of a water tower - placed there in modern(ish) times by the enterprising priests who built this place. Many of those priests knew their physics and obviously fancied better water pressure than the city would provide.

It was also conveniently close to hand and reasonably tall which was perfect for this activity. We used 10 phones and took a pressure reading on each in the lab before walking to the top of the hill* and taking a new reading there.

On our return we did the maths. Using the pressure difference, the density of air (1.225 kg/m3) and the value of g, we found the hill to be just over 16 metres high. I would have guessed a little higher, but the answers were all pretty much in agreement - only ranging from 16.1 m to 17.1 m

I've shown one of the calculations here

The pressure sensors are sensitive enough that you can even use this activity to find out the height of your school - or how high the 1st floor is above the ground floor at least - if you don't have a prehistoric burial mound convenient to your lab.

*I would love to report that the setting was as bathed in sunshine as it is in this photo but that is not the case. It was quite sunny when we set out, in fairness. But it rained heavily on us at the top (about one minute later) and then the sun came out again once we were inside again, soaking wet and doing the maths. Summer in Dublin.

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