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

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Discussion Overview

The discussion centers around the question of why various physical quantities such as temperature, voltage, and others are not all measured in kilojoules (KJ). Participants explore the nature of these quantities and their appropriate units of measurement, touching on concepts from thermodynamics and measurement systems.

Discussion Character

  • Conceptual clarification
  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants argue that temperature and voltage are state variables, while joules are units of work or heat, suggesting that different types of quantities require different units.
  • It is noted that voltage is defined in terms of joules per coulomb, indicating a relationship between energy and electric potential.
  • One participant mentions that temperature scales predate thermodynamics and are legacy units that are convenient for everyday use.
  • Another point raised is that energies can be measured in various units such as ergs, joules, and calories, with conversion rules existing between them.
  • Participants express frustration over the existence of multiple measurement systems, suggesting that a single system like the SI could simplify understanding.
  • A participant questions the appropriateness of using different units for different measurements, drawing analogies to other types of measurements like length and mass.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the appropriateness of measuring all quantities in kilojoules, with multiple competing views on the nature of measurement units and their relationships remaining evident throughout the discussion.

Contextual Notes

There are unresolved assumptions regarding the definitions of physical quantities and the historical context of measurement units. The discussion reflects a variety of perspectives on the relationships between different types of measurements.

Who May Find This Useful

This discussion may be useful for students and individuals interested in physics, measurement systems, and the conceptual foundations of physical quantities.

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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