Did you know that aeroplanes use air pressure to measure their altitude? In this video I'm going to show you how. Your smartphone and tablet have got a lot of sensors inside, for instance a barometer. Now I like to use this app called Firefox which has got lots of experiments inside but also enables you to just read the values of your sensors, for instance a pressure sensor. Now here on my tablet I can read the pressure in HectorPoscos and a thousand HectorPoscos is equal to a thousand minibars. So if I start the the app then I can read the air pressure and you can see the line actually going up and down a bit now it's going down and you might think that the air pressure is changing a lot but if you look at the units along the Y axis where it gives you the air pressure you can see that it only changes very slightly. So right now the air pressure is one thousand and twenty minibars. Now let's go into the elevator and see what happens next. Okay now we're inside the elevator and we're going to the third floor or the second level above, ground level and we're going to see what happens to the air pressure as we move up. So as you can see the air pressure is dropping and the water line at the start actually is a very flat line and if you stay here long enough then the air pressure, the normal closing in and the air pressure is here also levels off. So here on the third floor the air pressure is only one thousand and nineteen minibars. Now that means that the air pressure has dropped by one point two by about one point two minibars and you cannot extrapolate this to very high altitude so airplanes actually use a model that tells the airplane how air pressure drops with higher altitudes and also the model depends on the actual air pressure on ground level because due to atmospheric conditions the air pressure will vary between about nine hundred and fifty sixty millibars to up to one thousand twenty or thirty minibars. So you want to get that right otherwise you're off in your altitude which can be really dangerous. And another thing is that airplanes will also have to take into account that the earth is not level but sometimes goes out a bit for instance if there are mountains. So I hope to enjoyed this video about air pressure altitude and see you bye bye