Why are temperature/voltage/etc not measured all in KJ?

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The discussion centers on why various physical quantities like temperature, voltage, and mass are not measured in joules (KJ), which is a unit of work or heat. Participants clarify that temperature and voltage are state variables, distinct from energy, which is why they have separate units. Voltage is indeed related to joules, as it can be expressed in joules per coulomb, but temperature scales predate thermodynamics and are designed for practical use. The conversation highlights the complexity of measurement systems, noting that different units exist for different types of measurements, such as energy (measured in joules, calories, etc.) and length (measured in meters, miles, etc.). The importance of sticking to the SI system for consistency is emphasized, along with encouragement for students pursuing physics.
hexhunter
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why are temperature/voltage/etc not measured all in KJ?

ditto...
 
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Why?They're all other physical quantities.

Daniel.
 
dextercioby said:
Why?They're all other physical quantities.

Daniel.

Yah what he said :P

Joules is a unit of work/heat. Temperature is a state variable. Voltage is another state variable. Its like asking why isn't mass measured in Joules.
 
It's not necessarily thermodynamics.Voltage for example is not defined in thermodynamics.

Daniel.
 
Voltage is already measured in joules/columb - energy / unit charge.

Temperature scales were around long before thermodynamics, so they are a bit of a legacy unit. And they are conveniently sized for everyday use.
 
i mean, why aren't the energies measured in the same unit? also, chemical energy is measured in jouldes, in food atleast...

and i din't realize that joules were used for electricity

PS: I am only doing a single physics for my science GCSE, but next year i should hopefully be doing AS physics
 
Last edited:
Energies are measured in various units.It's either erg,or Joule,or Calorie and many more.Between them there are the so-called CONVERSION RULES.Just like in the scales for temperature...

Daniel.
 
We are unfortunate for having so many systems of measurement. This is not the case only with energy. Consider length, or mass. We have metres, miles, feet, inches, kg, ounces, pounds, and so on.
But just take the SI system as the official one, and you will have one basic unit for each quantity.
 
Hexhunter,

Why don't you use miles to weigh yourself? And why don't you order a metre of milk? We have different units to quantify different types of measurement, although (as Dex pointed out) they are often related, and you can usually describe one unit (Volt, like on a battery, for example) in terms of other units.

Good luck with your GCSE, stick at it and if you can do an AS in Physics then you'll have a better chance of getting into uni!
 

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