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we use torr to describe the pressure of our vacuum systems
we use psi (pounds per square inch) to describe the pressure of our compressed systems
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Log Scales (making numbers lie)
Not this log scale:
itThe log scale I'm talking about... It's math. sorry.
Log scale allows people to create graphs that show tiny things next to giant things really well by stretching out the distance between tiny numbers, and compressing the distance between huge numbers. the The powers of 10 does this really well.
Exponents and powers of 10
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the The little number above the 10's, called the exponent, is the number of zeros.
you can remember 'exponentexponent' because it exposes exposesthe number of zeros.
A negative exponent is how many zeros past the decimal place.
What's the difference between 107 and 103? the same difference between 10,000,000 and 1,000: over 9 million.
What's the difference between 10-7 and 10-3? the same difference between 0.00000001 and 0.0001: less (much less) than 1
-Different, but in both cases the difference is 4 orders of magnitude. look at the exponents: 7 - 3 = 4, tiny or huge, doesn't matter.
Linear vs Logarithmic
In linear counting the numbers increase one at a time. It's what we're used to. t's how we normally count: 1, 2, 3, 4, 5 etc...
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the log scale and the linear scale both start around 1 go up to 100,000. But what's different is how they get from 1 to 100,000. The second number in linear scale is 20,000, but in log scale the second number is only 10. Also in log scale the second to last number is 10,000, still much less than the second number in the linear scale: 20,000.
in the linear scale the distance between 0 and 500 is a small portion of the vertical aspect of the graph, but in the log scale that same distance takes up over half the graph; this is the stretching.
common Common units that use log scales: sound (decibels: dB), earthquakes (Richter magnitude)
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For molecules in UHV the mean free path is at least 200 miles. Any molecule in UHV is going to see the chamber walls thousands of times before it will see another molecule.
Vacuum Chambers
it's just a box for holding nothing.
Sadly the details of vacuum chambers and their construction is really beyond what this document is about (introduction to theory), but keep exploring!
For more details on Vacuum System parts and how they actually work, see the confluence pages on vacuum components