Where do these constants in equations come from?

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Discussion Overview

The discussion revolves around the origins and meanings of integer and fractional constants in physical equations, such as those for mean-square speed and kinetic energy. Participants explore how these constants are derived and their implications in physics and mathematics.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants express curiosity about the origins of constants like 3 and 0.5 in equations, questioning their apparent arbitrariness.
  • One participant suggests that the constant 3 in the mean-square-speed equation arises from the dimensionality of space and its role in the statistical treatment of the ideal gas law.
  • Another participant claims that the constant 0.5 in the kinetic energy equation comes from the integral of velocity, which relates to the definition of work and Newton's Second Law.
  • Some participants note that the derivation process often clarifies why certain constants appear as integers or simple fractions.
  • One participant mentions the convenience of using simple constants in empirical investigations, highlighting that very close values can often be approximated as 1.
  • Another participant counters that not all constants are integers, citing examples like the golden ratio and pi, which are irrational numbers.

Areas of Agreement / Disagreement

Participants generally agree that the derivation of equations can explain the appearance of certain constants, but there is disagreement regarding the nature of these constants, with some asserting that they are often integers or simple fractions, while others point out the existence of irrational constants.

Contextual Notes

Some claims about the origins of constants depend on specific definitions and interpretations of physical laws, and the discussion does not resolve the broader implications of these constants in various contexts.

SticksandStones
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Something I've always wondered: how did Physicists and Mathematicians of years past discover equations with these integer (and even fraction) constants in them?

Take for example the mean-square-speed equation:
[tex]\mu \equiv \sqrt{\frac{3RT}{M_{m}}}[/tex]

or Kinetic Energy:
[tex]\frac{1}{2}mv^{2}[/tex]
How do they discover this 3 and .5? It seems arbitrary.
 
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SticksandStones said:
Something I've always wondered: how did Physicists and Mathematicians of years past discover equations with these integer (and even fraction) constants in them?

Take for example the mean-square-speed equation:
[tex]\mu \equiv \sqrt{\frac{3RT}{M_{m}}}[/tex]

or Kinetic Energy:
[tex]\frac{1}{2}mv^{2}[/tex]
How do they discover this 3 and .5? It seems arbitrary.
This 3 comes from dimensionality of space... which plays a role in the statistical treatment of the ideal gas law.
This .5 comes from the integral of v dv, which arises from the definition of work and Newton's Second Law.

These relations are derived from first principles...
 
Last edited:
The integer and even fraction constants are usually pretty apparent when you go through a derivation.
 
SticksandStones said:
Something I've always wondered: how did Physicists and Mathematicians of years past discover equations with these integer (and even fraction) constants in them?

Take for example the mean-square-speed equation:
[tex]\mu \equiv \sqrt{\frac{3RT}{M_{m}}}[/tex]

or Kinetic Energy:
[tex]\frac{1}{2}mv^{2}[/tex]
How do they discover this 3 and .5? It seems arbitrary.

Hyperphysics is one good site to explore some of these questions, e.g.

http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/kintem.html
http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/molke.html
http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/maxspe.html
 
Thanks for the links Astronuc.

Something I forgot to leave out of my original post is my surprise at how often it turns out to be an integer (or simple fraction) that it is multiplied by.
Although I guess going through and deriving it shows why.
 
SticksandStones said:
Thanks for the links Astronuc.

Something I forgot to leave out of my original post is my surprise at how often it turns out to be an integer (or simple fraction) that it is multiplied by.
Although I guess going through and deriving it shows why.

When it comes to empirical investigation of constants, remember that, say, 100000000000000000000/100000000000000000001, is pretty close to 1. It is convenience to choose one; and the fact that there is no measurable difference.
 
its not ALWAYS an integer... A famous number for example is the golden ratio, which is like (1+sqr(5))/2 ~= 1.62
Or... number pi? Area of Circle = pi*r^2 ?
Many times in formulas you have square roots of things, which are irrational numbers... there are PLENTY of examples where the constants are not integers.
 

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