2520: Symbols

2021-09-24T21:24:56Z

Ajaxgb: /* Explanation */ Better explanation of pi vs tau

{{comic
| number = 2520
| date = September 24, 2021
| title = Symbols
| image = symbols.png
| titletext = "röntgen" and "rem" are 20th-century physics terms that mean "no trespassing."
}}

==Explanation==
{{incomplete|Created by an internet argument - Please change this comment when editing this page. Do NOT delete this tag too soon. Bare-bones explanation is in, but needs much more detail.}}

This comic refers to notation commonly used in various fields of math and science, and humorously comments on their implications.

d/dx and ∂/∂x are both used to represent {{w|derivative}}s in calculus and related fields. d/dx is most commonly used in introductory and basic calculus, and is moderately difficult but well within reach for an undergrad math student. On the other hand, ∂/∂x is the symbol for a {{w|partial derivative}}, indicating a problem involving multivariable calculus, which is a level of difficulty above single-variable calculus.

ħ (pronounced 'h-bar') is a symbol used for {{w|Planck's constant}}, a universal constant in quantum physics equal to the energy of a photon divided by its frequency.

Re, {{w|Reynolds' number}}, is used in modelling the flow of fluids. Fluid flow cannot usually be modeled analytically and so a complex numerical model is necessary. (Note: Reynolds' number is commonly written '''Re''' rather than '''Re'''; it's unclear if this is intended to convey something else).

Ta4 - Tb4 is a term that represents {{w|blackbody radiation|blackbody}} radiative heat transfer between two surfaces with different temperatures. Solar radiation can be modeled with this equation.

NA is {{w|Avogadro's number}}, which is used in chemistry for calculating the number of molecules in a mass of substance. Its use implies a chemistry problem where relative concentrations and orders of magnitude are important; if a mistake is made the concentration of a potentially dangerous chemical could be far too strong or too weak.

μm and mK (micrometers and millikelvin) are very small units of length and temperature respectively. Any equipment that is operating in these units will be incredibly finely calibrated and thus very expensive. Millikelvins would measure temperatures barely above {{w|absolute zero}}, suggesting sensitive experiments probing quantum mechanical behavior that would likely only exist in an advanced lab.

nm and eV ({{w|nanometer}}s and {{w|electronvolt}}s) are also small units of length and energy. Nanometres in particular are commonly used to refer to wavelengths of light, and therefore might be seen when working with lasers, which you should definitely not shine in your eye. Electron volts are a measure of energy in particle physics; {{w|particle accelerator}}s produce intense radiation which should definitely not be directed toward your eye.

mSv ({{w|millisieverts}}) are a unit of radiation exposure. Randall's comment may be referring to [https://xkcd.com/radiation/ this chart], to internet trolls debating the effects of radiation like 5G networks, or to fans of the [[2163|Chernobyl series]]

mg/kg and μg/kg (milligrams per kilogram and micrograms per kilogram) are units of toxicity; the average lethal dose of a chemical with toxicity 1 mg/kg would be one milligram of chemical for every kilogram the person weighs. Such a chemical would be quite dangerous; since micrograms are much smaller than milligrams, any chemical with toxicity measured in μg/kg would be a lot worse.

Finally, the comic references {{w|pi}} and {{w|Turn (angle)|tau}}. Pi is defined as the ratio of a circle's circumference to its diameter, while tau is defined as the ratio of a circle's circumference to its radius (or pi times two). Pi is the more popular circle constant and leads to simpler area and volume formulas, but proponents of tau argue that the radius is a more fundamental concept than the diameter and is more commonly used in various areas of geometry, making tau a cleaner choice of constant. The joke here is that whichever constant you attempt to use, it will probably be the wrong one for what you are trying to achieve.

Finally, the title text lists two units for radiation, röntgen and REM (röntgen equivalent man). The SI unit equivalents for these are coulomb/kilogram and sieverts, respectively. Using non-SI units can seem outdated, hence the 20th-century part, and areas with lots of radiation are dangerous and should be avoided, hence the no trespassing part.

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}

;d/dx
:an undergrad is working very hard
;∂/∂x
:a grad student is working very hard
;ħ
:oh wow, this is apparently a quantum thing
;Re
:someone needs to do a lot of tedious numerical work; hopefully it's not you
;(Ta4 - Tb4)
:you are at risk of skin burns
;NA
:you are probably about to make an incredibly dangerous arithmetic error
;µm
:careful, that equipment is expensive
;mK
:careful, that equipment is very expensive
;nm
:don't shine that in your eye
;eV
:definitely don't shine that in your eye
;mSv
:you are about to get into an internet argument
;mg/kg
:go wash your hands
;µg/kg
:go get in the chemical shower
;π or τ
:whatever answer you get will be wrong by a factor of exactly two

{{comic discussion}}

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2520: Symbols