Do some scientists create equation that arent based on si units.

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Discussion Overview

The discussion revolves around the use of different unit systems in scientific equations, particularly whether equations are inherently tied to SI units or if they can be expressed in alternative units. It explores the implications of using non-SI units in various fields, including physics and astronomy.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • Some participants note that while SI units are standard, equations can be expressed in different unit systems, such as cm, kg, and minutes.
  • One participant argues that equations are not "meant" for a specific unit system but can be adapted to different units, with a preference for SI in most textbooks.
  • Another participant highlights that certain unit systems, like those where fundamental constants equal 1, can simplify equations but are impractical for everyday use.
  • It is mentioned that Gaussian units can simplify electrodynamics equations, indicating that different fields may prefer different unit systems.
  • Participants emphasize the importance of specifying the unit system used in any equation to avoid misunderstandings, citing the Mars Climate Orbiter incident as a cautionary example.
  • Some fields, such as astronomy, may find SI units inconvenient, with light-years being a common alternative, though there is a discussion about the appropriateness of using parsecs instead.

Areas of Agreement / Disagreement

Participants express differing views on the necessity and appropriateness of using non-SI units, with some advocating for their use in specific contexts while others emphasize the importance of SI units. The discussion remains unresolved regarding the best practices for unit usage in scientific equations.

Contextual Notes

There are limitations regarding the assumptions made about unit systems, and the discussion does not resolve the appropriateness of different units in various scientific contexts.

jaydnul
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The base units are meters kg and seconds, right? So are some equations meant to use a different set, like cm kg minutes or something. And is it always assumed to be si unless told otherwise?
 
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any equation's variables can be converted from one unit to another; no equation is "meant to use a different set" but can be written in another way. In most physics textbooks only SI units are used.
 
In certain cases equations might be simpler in some particular system of units. A particularly famous one is that where the units are such that all the fundamental constants (Planck's constant, speed of light, gravitational constant) equal 1 and simply omitted from the equations. These units, however, are completely unsuitable for practical use. A more practical example is the Gaussian units, which partially overlap with SI. In these units, equations of electrodynamics are somewhat simpler, so many texts use them. In non-relativistic classical mechanics equations are usually independent of the choice of units.

In any case, anyone using any equation ought to mention assumptions on the units.
 
People use non-SI units every day. Classic example would the fuel consumption of your car being specified in miles per gallon.

However you should never assume any particular units have been used. Always check and recheck..

http://en.wikipedia.org/wiki/Mars_Climate_Orbiter

However, on September 23, 1999, communication with the spacecraft was lost as the spacecraft went into orbital insertion, due to ground based computer software which produced output in Imperial units of pound-seconds (lbf-s) instead of the specified metric units of Newton-seconds (N-s). The spacecraft encountered Mars at an improperly low altitude, causing it to incorrectly enter the upper atmosphere and disintegrate.
 
In some fields of work it's vey inconvenient to use SI base units such as the meter. Astronomers frequently work in "light years" for example.
 
What I hear from some friendly astronomers is that light-years as a distance unit has a ring of SciFi affection to it. Parsec is perceived as the more appropriate unit.
 

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