It's been a summer to forget.
25 June - 6 Aug only averaged 1006mbar (STP is 1013mbar).
In 6 wks TC clock gained 2s. Oh no!
Why? Low air pressure = low density which decreases buoyancy of pendulum bob so apparent 'g' is more. Period=2π√(L/g) so clock goes faster. @TrinCollCam
And here's pressure measured on the train from London King's Cross to Cambridge. Slow pressure drop as altitude rises about 80m to Stevenage but the big dips are when the train goes through tunnels.
Amazed that I can measure the height of the clock tower with my phone. Barometric pressure varies with height. I had to unlock the door on the way up and on the way down. Hence the pause. This shows a height of 1.35mbar or 11.5 meters. Exactly right!
Some background to The Great Court Run is here en.wikipedia.org/wiki/Trinit… - yes the idea is to run around Great Court (about 339 metres) in the time it takes for the clock to strike 12. Here is the run in 2012 youtube.com/watch?v=enmeCn6G…
4. Then there's air density. The spinning 'fly' controls speed by air drag and that depends on air density. It's clear then that the best chance of beating the bells is on a cold dry day 3 days after winding. .../5
2. This is in part because of air density (tempreature/pressure/humidity) but the biggest effect is that the weight driving the bells runs onto a second layer on the drum which gives a bigger torque and therefore faster striking .../3
The Great Court Run is coming up. I've done an analysis over two years 2018-2020 and the time it takes to strike 12 averages 48 seconds but sometimes as slow as 46 seconds and as long as 50 seconds .../2
