Download - Units of Pressure (interestingly, while the ‘Bowie’ isn’t one of them, Mercury is related)
![Page 1: Units of Pressure (interestingly, while the ‘Bowie’ isn’t one of them, Mercury is related)](https://reader030.vdocument.in/reader030/viewer/2022032607/56649ebb5503460f94bc3b0d/html5/thumbnails/1.jpg)
Units of Pressure
(interestingly, while the ‘Bowie’ isn’t one of them, Mercury is related)
![Page 2: Units of Pressure (interestingly, while the ‘Bowie’ isn’t one of them, Mercury is related)](https://reader030.vdocument.in/reader030/viewer/2022032607/56649ebb5503460f94bc3b0d/html5/thumbnails/2.jpg)
Some Historical PerspectiveRemember my demo in class with the upside-down flask of water? If you make that big enough, you can use it to measure pressure:
This is the world's simplest barometer.
When air pressure goes up, morewater gets pushed in.
When air pressure goes down, waterflows out and the height gets shorter.
vacuum
air pressure
![Page 3: Units of Pressure (interestingly, while the ‘Bowie’ isn’t one of them, Mercury is related)](https://reader030.vdocument.in/reader030/viewer/2022032607/56649ebb5503460f94bc3b0d/html5/thumbnails/3.jpg)
ProblemIf you use water, it needs to be >10 m tall.
Solution: use a liquid that is much more dense...
....mercury!
Now it only needs to be less thanone meter.
Measure the height of the column, andyou have your pressure in units of mmHg
![Page 4: Units of Pressure (interestingly, while the ‘Bowie’ isn’t one of them, Mercury is related)](https://reader030.vdocument.in/reader030/viewer/2022032607/56649ebb5503460f94bc3b0d/html5/thumbnails/4.jpg)
Unit Number OnemmHg: Literally, the height of a column of mercury that the current pressure could support.
Also called 'torr': named after Torricelli, who invented the mercury barometer.
These are the same unit, just with different names.
5232 mmHg = 5232 torr
![Page 5: Units of Pressure (interestingly, while the ‘Bowie’ isn’t one of them, Mercury is related)](https://reader030.vdocument.in/reader030/viewer/2022032607/56649ebb5503460f94bc3b0d/html5/thumbnails/5.jpg)
Some More HistoryThe barometer is good for measuring atmospheric pressure, but what if you want to measure inside a container?
Use a manometer:
One side is attached to your container
The other side is open to the air
If the pressures are the same, the sides are even.
![Page 6: Units of Pressure (interestingly, while the ‘Bowie’ isn’t one of them, Mercury is related)](https://reader030.vdocument.in/reader030/viewer/2022032607/56649ebb5503460f94bc3b0d/html5/thumbnails/6.jpg)
Some More HistoryThe barometer is good for measuring atmospheric pressure, but what if you want to measure inside a container?
Use a manometer:
But if your container has higher pressure,the mercury gets pushed down.
The difference in height tells you how much higher the container is than the atmosphere.
![Page 7: Units of Pressure (interestingly, while the ‘Bowie’ isn’t one of them, Mercury is related)](https://reader030.vdocument.in/reader030/viewer/2022032607/56649ebb5503460f94bc3b0d/html5/thumbnails/7.jpg)
Unit Number TwoAtmospheres (atm): because sometimes it's nice to just have atmospheric pressure have a value of one.
(since atmospheric pressure varies from day to day and with elevation, your atmospheric pressure is not guaranteed to be 1 atm, but it will be close)
1 atm = 760 mmHg
![Page 8: Units of Pressure (interestingly, while the ‘Bowie’ isn’t one of them, Mercury is related)](https://reader030.vdocument.in/reader030/viewer/2022032607/56649ebb5503460f94bc3b0d/html5/thumbnails/8.jpg)
Unit Number ThreePascals (Pa): METRIC/ SI!!
Absolutely necessary for physics to make units match up for equations ( 1 Pa = 1 kg/m*s2)
1 atm = 101,300 Pa
![Page 9: Units of Pressure (interestingly, while the ‘Bowie’ isn’t one of them, Mercury is related)](https://reader030.vdocument.in/reader030/viewer/2022032607/56649ebb5503460f94bc3b0d/html5/thumbnails/9.jpg)
Unit Number Fourbar: Actually just a 100,000 Pa. Used as a replacement for atm because 1 bar is approximately atmospheric pressure. But generally a little bit lower.
1 bar = 750 mmHg = 0.986 atm
You will also see millibar used (mbar). Which is actually just 100 Pascals.
![Page 10: Units of Pressure (interestingly, while the ‘Bowie’ isn’t one of them, Mercury is related)](https://reader030.vdocument.in/reader030/viewer/2022032607/56649ebb5503460f94bc3b0d/html5/thumbnails/10.jpg)
Unit Number FivePounds per square inch (psi): Don't use this except in your tires.
1 atm = 14.7 psi
![Page 11: Units of Pressure (interestingly, while the ‘Bowie’ isn’t one of them, Mercury is related)](https://reader030.vdocument.in/reader030/viewer/2022032607/56649ebb5503460f94bc3b0d/html5/thumbnails/11.jpg)
Some Really Obscure OnesMeters of Sea Water: used by divers.
Barye: used by people who still measure volume in hogsheads.
Technical atmosphere (at): used by people who hate all that is good and right in the world.
Feet of water (ftH2O): now they're just mocking me.
![Page 12: Units of Pressure (interestingly, while the ‘Bowie’ isn’t one of them, Mercury is related)](https://reader030.vdocument.in/reader030/viewer/2022032607/56649ebb5503460f94bc3b0d/html5/thumbnails/12.jpg)
Which Ones Will We Use?mmHg: still widely used for historical reasons
atm: convenient for relating to something all around you.
Pa: metric/ SI
![Page 13: Units of Pressure (interestingly, while the ‘Bowie’ isn’t one of them, Mercury is related)](https://reader030.vdocument.in/reader030/viewer/2022032607/56649ebb5503460f94bc3b0d/html5/thumbnails/13.jpg)
Summary• Lots of units of pressure.
• Many of them are crazy.
• You should recognize bar, torr, and psi, but we will not use them.