The #phyphox app from @rwth_phyphox gives you direct access to the output of many #sensors in your smartphone. Next time you have a long ✈️flight, quantify turbulence or just check on your phone when the toilet rush is over. (Warning: #scicomm #physics thread ahead!👇) 1/n 
That’s why your crisps package expands after take-off and the empty plastic bottle appears auto-crushed after landing. The pressure sensor can be used to estimate elevation when being on earth. But it is so sensitive it feels when airplane toilets are flushed. 3/n
Airplane toilets are #vacuum based (you all know the sound). Actually, there is no suction, but cabin air pushes the toilet’s contents towards the vacuum tank (this one is for you, @lievenscheire!). Hence the air pressure drops in the cabin. 4/n
I would #guestimate the amount of air displaced at about 25-50 liter, based on the relative pressure change and the size of the cabin (any vacuum toilet manufacturers in the audience?) 5/n
The drop is 0,2 hPa (0,003 psi), after which the cabin pressure is automatically increased and quickly stabilized. The A321 has two lavatories in the rear, so the average visit is 105 seconds. People were queueing after we had some turbulence. 6/n
You can also quantify this turbulence with the accelerometer, which measures the acceleration in three dimensions (so that your phone knows its orientation and whether it is falling). This is the reading during some moderate shaking: 7/n
I oriented my phone horizontally and pointing towards the front. So you get separate readings for the left-right direction, forward-backward and up-down. During turbulence, there is hardly an acceleration in the forward direction, most is up-down and left-right. 8/n
Bringing all accelerations together, it got to 4 m/s² during the strongest shakings, or a bit less than 0.5g, which is probably “light to moderate turbulence”. Interested? Find the app here: phyphox.org @rwth_phyphox #iteachphysics 9/n
