I know what pressure is, just not how it works, for instance, why do things get sucked out of planes at high altitudes if there is a hole, what is a depressurization, why do planes need to be pressurized, and any other info on pressure. thanksadam

Well, you will probably find a lot of info by doing a Google, but here

And just to add one thing to his explanation - people aren't sucked out of a plane, they're blown out. In other words, high pressure always goes to low pressure.

Thanks alot, but if the aircraft cabin is sealed, and say, when the plane is on the ground, with the doors open, the cabin would be a 14.7 psi, and since it is sealed when its in the air, why do they need pumps to keep the pressure high, where is the pressure that was at ground level going to go? And also can someone explain the stages a plane takes with pressurizing, like when does the pressure increas and drop, and also, why do your ears pop?adam

On the ground we are all under HIGH pressureUp at high altidude the pressure is LOW.The arrows show the amount of air pressure::)So, how do you keep the pressure high to keep us comfortable? Pressurize the cabin. The best example is a balloon.Find one and blow it full of air - thats a plane getting pressurized :)Air is pumped into the plane to make the CABIN altitude about 8000 feet. So thats the same as standing on a mountain thats 8000 feet high - comfortable. Although newer jets can have a 6000 ft cabin altitude.Now the air being pumped in has to have somewhere to go...so there are bleed valves in the fuselage for that. Air is pumped in and then goes out through those holes to keep the pressure at 8000 feet.So in the cockpit the pilots have a guage showing Cabin Altitude :)So pressurization FOOLS the body into thinking that its still kinda at ground level when actually outside the plane you would pass out & die in minutes!Pressurization pushes against the inside of the plane (like if you push your hand against a wall). Its this force that helps keep the cabin doors sealed tight (now you know why they are designed like plugs) and its this same force pressing against your ear drums. As you climb in an aeroplane the air pressure DECREASES. Problem is that there is still air trapped in your inner ear system and this causes your ear drums to push outward:-------->) = Pushing outward *Pop*Now the plane has to land. Now the plane CAN land with pressurization on but they wont be able to open the doors & it wont be comfortable!So they have to let the cabin pressure INCREASE (remember the lower you go the HIGHER the pressure) to equalize it with the outside pressure. They adjust this pressure gradually.....the pressure on your ears increases slowly - pushing your ear drums inward....and you feel your ears pop:(:)

>cabin would be a 14.7 psi, and since it is sealed when its in>the air, why do they need pumps You can NOT keep 14.7 psi inside all the way to high altitude - it would require such heavy airframe to withstand the enormous pressure differential that it would be uneconomical. You have to gradually reduce the pressure inside the cabin while airplane is climbing. Pumps provide fresh air - we humans consume quite a bit of oxygen/air !Michael J.http://www.reality-xp.com/community/nr/rsc/rxp-higher.jpg

OK Adam, one question you asked was why things get sucked out at high altitudes. Others have answered your question to one degree or another, but here's some numbers for you (I taught Weather and Climate before, so that's where I'm getting my info from).First, air pressure decreases with altitude. Others have said that here, but it's important to realize it decreases exponentially. That is, air pressure decreases very rapidly near the surface, and less rapidly higher up. Fully 1/2 of all earth's atmosphere lies below 18000 feet! When you consider that the atmosphere goes up for more than 100,000 feet, you can appreciate how rapidly the RATE of CHANGE is down low.Alrighty, aircraft are pressurized so that the body can fly at high altitudes. Jets and turboprops (and now some pistons) like to fly high because it saves in gas mileage (less air = less drag), you can often get higher and more favourable winds up high, etc. However, the body can't tolerate altitudes much above 15,000 feet very well, and technically you should be on oxygen after about 10,000 feet. Folks living in the upper levels of the Andes won't have the problems most of us do who live within a couple of thousand feet of sea level, but even then, you see Sherpas dying from the extremes while climbing Mount Everest (28,000 feet). So, you make a "tube" airtight (or so we'd like to think - they ALL leak to some degree), and pump air into it, then go up really high. That's a pressurized airplane for you.So, let's say you take off from sea level, where the pressure is 14.7 lbs per square inch (psi). Let's say too that this is a very modern, new jet that can maintain that level of pressurization right to 30,000 feet (not many can, but they can come close, so we'll go with that for now). So, the pressure inside the cabin is still at 14.7 psi. However, the pressure at slightly under 30,000 feet (outside) is a mere 4.5 psi! That's a 10.2 psi difference in pressure. Now, the laws of physics being what they are, all things will try to find a neutral position in this world, so high pressure will always try to flow "downhill" to low pressure. In the cabin you have high pressure, and outside you have low pressure. What is preventing this equalization though, is the cabin walls and windows. That's great. Let's say the window is about 14" x 10" (roughly an airliner window size - you'll see why they make them small in a minute). You are sitting beside "window A". All of a sudden, that window suffers a structural failure (EXTREMELY rare, fortunately). Now all that high pressure air inside has an escape route and they all rush towards that opening in a big rush, at the same time. You, being next to it, are carried by that air and now are blocking the air's escape route. However, your body just isn't as strong as plexiglass, but for the moment, you plug that window with it. You now have 14.7 psi on one side of you, and 4.5 psi on the other. Given the area of the window (14 x 10 = 140 square inches), you now have a total force of 10.2 psi (the difference between the inside and outside pressures) x 140 square inches, which equates to 1428 lbs of force against one side of your body, while the other side has only 4.5 psi x 140 sq in = 630 lbs on your body. That's about a 740 lbs difference from one side of your body to the other. Can you lift 740 lbs? You, my friend, are going outside that window. It won't matter that your body doesn't fit through there - the force differential will take care of that fairly quickly. Of course, you'll likely be shredded as you go through the window, so you won't really be around to "enjoy the view". Can you now see why they make those windows so small? Those windows have to stand up to extreme pressures, and the smaller they are, the better able they are to do that.Now, that pressure will equalize reasonably quickly, so if you aren't right next to that window, then chances are you'll stay in your seat, if your seat belt is done up. But remember this - the winds generated inside the airplane with all that air rushing to the outside, for however brief a time, will take a lot of things with it, and create havoc inside the airplane, including instant fog and complete chaos, so regardless of whether you stay in or not, it won't be a fun environment.I've simplified things a bit here, but I hope that answers your question about why things get sucked out (and yes, you can consider yourself either being sucked out or blown out - it depends on which side of the fuselage you are standing as to which term applies :-) ). Go grab a book in the library on the atmosphere. It can make for some extremely interesting reading :-).Glenn

Thanks alot for the info, i really appreciate it.adam

My pleasure :-). Enjoy!Glenn

One thing I find amazing, and one of the great "mistakes" often made in movies, is how the cabin door stays "shut" when at altitude.If you have seen the first Charlies Angels movie, you will notice the ridiculous beginning, where a man drags another man to the service exit, flings open the door and bails.On today's aircraft, that is impossible.If you notice, when the cabin door is opened, the door is first pushed in, then opens out.As a result, the cabin pressure needs to be equalized to even allow the door to be budged.If the difference between cabin pressure and outside pressure were even a scant 1PSI, the weight required to "pull open" the door, would be approx (assume 5.5 ft x 2.5 ft door (which is small as it is a Dash 8 door) Thats 66 x 30 inches or 1980 square inches.So with even a "small" 1psi difference in pressure, an inwould pull exceeding 1900 lbs of force would be required to break the seal and open the door. At altitude, the pressure differential between the cabin and the atmosphere is over 5 times that amount.Even the "wing" emergency exits would require super human strength to pull inward at pressure.As a result, with any aircraft under proper pressuriztion, it is physically impossible to open the door in flight. Yes, a cabin can lose pressure many ways, but pulling open the cabin door isn't one of them.

Quote: If you notice, when the cabin door is opened, the door is first pushed in, then opens out.Not entirely true, not every aircraft has plug type doors. Take for example a Beech King Air with an outward hinged door (or even the DHC-8 mentioned in this thread). Some, but not all outward hinged doors will use an over-center mechanism where the door will move inward a fraction of an inch before releasing and opening (quite uncommon due to complexity of design). Most types of outward hinged doors use "pins" that protrude from the sides of the door frames and into strengthened sections of the airframe, therefore the only force you would be battling against to get the door open would be the pressure of the pins inside the barrels in the airframe, a VERY small force due to the size of the pins. For this reason doors are designed with pressure locks that sense pressure both inside and outside the aircraft. Generally at any point above 0.5PSI difference, there is a mechanical lock that moves into place and physically blocks the door lock mechanism from moving.