# Thread: absolute temperature vs absolute pressure!

1. is there any absolute pressure? (only those reply who fully understand the concept of absolute temperature ie 0K or -273C)

after replying this try on following
absolute mass
absolute density
absolute time etc

2.

3. The thing that makes the Kelvin scale of temperature "absolute" is that it has a non-arbitrary zero point. The units of K are arbitrary and so not "absolute". The same is true of mass, length and density. And, I suppose, time if you set zero to the big bang. But in all cases we (normally) measure them in man-made units.

You might also want to look at Natural units - Wikipedia, the free encyclopedia

The thing that makes the Kelvin scale of temperature "absolute" is that it has a non-arbitrary zero point. The units of K are arbitrary and so not "absolute". The same is true of mass, length and density.

5. Measurements can be relative or absolute. Relative means that something is measured by comparison to something else. For example speed is always relative, temperature in centigrade/Celsius is relative to the freezing/boiling points of water.

An absolute measurement does not need to be compared to anything else. The Kelvin has an absolute origin. Similarly, there is an "absolute zero" for mass and length and therefore for derived units such density or pressure.

But the size of one degree in Kelvin doesn't relate to anything absolute; it is an arbitrary man made unit; based (originally) on the comparison of the freezing and boiling point of water. There are units that could be considered absolute as well (hence the link).

6. Absolute zero pressure would be a perfect vacuum. This would be PSIA by standard conventions. We normal use PSIG (gauge) wich gives us the differential between atmospheric pressure at your location vs. the pressure of what you are measuring. There is also PSID (differential) which uses two inputs to your pressure measuring device, and is as stated. Shows differential pressure.

An example of normal usage for PSIA (absolute) is a barometer.

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