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Background

This question was received rather negatively by the community for its naive understanding of units of force. Put simply, it asked what would happen if you punched somebody with 172500N of force. It's off-topic for WB.SE, and it [probably] wouldn't be received too well on Physics.SE.

Proposal

Inspired by xkcd, I hope to establish some intuitive(ish) reference points for various metric units. Many people could estimate a centimeter as about the width of a finger, but how much pressure is one megapascal? Sure, it's defined as 1e6 Pa, but what's that mean to the root user?

Answers to this question should be written for a single unit. The format is as follows:


Unit name

Base SI unit: (mathjax describing unit and using only SI base units)
Common units: (unit of measure commonly used. If there's an equivalent measure in Imperial units, include it as well.)

Range name

Unit
Value   Description
Value   Description

Defined Constants:

  • Constant - description (Link to the wikipedia page for that constant.)

Current units defined in this question:

Units that need a definition:

  • Momentum (maybe)
  • Luminance
  • Conductance
  • Capacitance
  • Pressure
  • Density

Feel free to add more.

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  • 3
    $\begingroup$ I do think this might be borderline useful, but note that we've had ample discussion about introducing terminology specific to Worldbuilding SE and such proposals haven't gone well, for good reason IMO. A post should be understandable to someone with the correct subject matter expertise even if they have zero experience with the community. $\endgroup$ – user Feb 15 '18 at 8:07
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    $\begingroup$ This might be a good resource for people to reference in answers, but I don't think this will help people ask questions. If the OP does not have at least a high-school level understanding of physics / units, having intuitive reference points will not help him/her either. Also if those parts of the question are way off, imo that shows a complete lack of research. So what I'm saying: If the units are wrong, the rest of the question won't be high quality either. $\endgroup$ – Raditz_35 Feb 15 '18 at 9:44
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    $\begingroup$ BTW en.wikipedia.org/wiki/Orders_of_magnitude_(magnetic_field) I tought about doing this one myself but it already exists. Maybe the link helps someone? I don't want to just copy from wikipedia. $\endgroup$ – Raditz_35 Feb 15 '18 at 9:49
  • $\begingroup$ @Raditz_35 A reference page was really one of my intended goals, actually. I freely admit that questions on units will get closed a lot more often in main with a link to a specific answer in this question. Is this a good thing? $\endgroup$ – Jakob Lovern Feb 15 '18 at 18:34
  • $\begingroup$ While I see the motivation behind this, I doubt most people will know about this post, and among those who do, most would not remember about it before posting a question or answer. Furthermore any conversions or references needed are one just one browser tab away, anyway. $\endgroup$ – The Square-Cube Law Mar 9 '18 at 20:12
  • $\begingroup$ Eh, it was a call to arms unanswered. At the least, it'll stop someone from doing this in the future. $\endgroup$ – Jakob Lovern Mar 9 '18 at 21:29
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Energy and Power

Energy is measured in SI units of Joules. Power is the delivery of energy per second, and is measured in SI units of Watts. A Watt is one Joule per second.

Energy

Base SI unit: $\frac{m^2*kg}{s^2}$
Common units: Joule (J), kilowatt Hour (kWh)

'Orders of magnitude (Energy)' on Wikipedia

Joules
1.6e-23   Energy of a photon from a microwave oven
5.0e-15   Energy of a n X-ray photon
8.2e-14   Mass-energy equivalent at rest of an electron
3.4e-11   Energy released by the fission of one U-235 atom
1.6e-7    The kinetic energy of a flying mosquito
1.0e0     The impact energy of an apple, dropped from 1m height
1.0e2     Energy stored in the capacitor of a flash-producing camera
1.8e3     Kinetic energy of a M16 rifle bullet
4.5e4     Energy released by burning 1 gram of gasoline
6.0e5     Kinetic energy of a 2 ton automobile at 90 km/h
1.1e8     Total energy burned while bicycling the Tour de France
3.0e9     Kinetic energy of a Boeing 767 in flight
4.2e9     Energy equivalent of 1 ton of TNT
6.3e13    Orbital kinetic energy of the ISS
2.1e17    Energy released by Tsar Bomba, the most powerful nuclear weapon
6.8e19    Energy in the world's yearly electricity production
5.0e23    Energy in the Chicxulub impact (that killed the dinosaurs)
3.8e28    Kinetic energy of the Moon relative to the Earth
2.0e32    Gravitational binding energy of the Earth
2.7e33    Kinetic Energy of the Earth's orbit relative to the sun
1.0e44    Energy released in a supernova

Power

Base SI unit: $\frac{kg*m^2}{s^3}$
Common units: watt(W), horsepower(hp)

'Orders of magnitude (Power)' on Wikipedia

Watts
1.0e-20   Power of the signal from Galileo space probe as it orbited Jupiter
1.0e-16   Power of a GPS signal as received by your phone or watch
1.0e-12   Power consumption of the average human cell
1.0e-6    Power consumption of a mechanical wristwatch
7.0e-2    Antenna power output of a household wireless router
8.0e0     One human operating a hand-crank
4.0e2     Approximate peak power consumption of a GPU
7.5e2     One horsepower
5.0e3     Photosynthetic energy production of a square km of ocean
3.0e6     Power output of a locomotive
2.1e9     Peak power output of the Hoover dam
1.8e13    Power consumption of humanity
7.5e13    Global net primary productivity
1.1e15    World's most powerful laser pulse (there are competing claims)
1.4e15    Heat flux of the Gulf Stream
1.7e17    Solar energy that strikes the Earth / Kardashev I civilization
3.8e26    Luminosity of the Sun / Kardashev II civilzation
5.0e36    Luminosity of the Milky Way / Kardashev III civilzation
3.6e49    Power emitted by black hole merger GW150914
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Velocity

Base SI units: $m/s$, $\theta/s$
Common units: mph, kph, m/s, %C

Note: This answer includes both linear and angular velocity.

Linear Velocity

'Orders of magnitude' on Wikipedia

Atom smashers

People and cars

kph m/s 
5   1.5 Walking
13  3.5 Jogging
25  7   Sprinting
35  10  Fastest human
45  13  Housecat
55  15  Rabbit
75  20  Raptor
100 25  Slow highway
110 30  Interstate (65 mph)
120 35  Speed you actually go when it says “65”
140 40  Raptor on hoverboard

Things that fly

kph
  893  Boeing 747-300 cruise speed
7,274  X-15 (see https://what-if.xkcd.com/58/)

Space, orbital

kph
     2,286  Moon's linear orbital velocity around the Earth
    11,052  linear velocity of geostationary 
    27,600  ground velocity of the International Space Station
   108,000  linear velocity of Earth as it orbits the Sun 
   720,000  linear velocity of the Sun around the center of the galaxy
18,000,000  S2's orbital speed around the black hole Sagittarius A*
     ??  velocities of various objects in orbit around earth

Space, nonorbital

kph
    39,897  maximum velocity of Apollo 11 (earth reference point) 
    61,200  Velocity of voyager space probe (sun reference point)
   252,792  fastest we've ever made anything go (Helios 1)
 1,440,000  velocity of hypervelocity stars

Space, relativistic

%c
<1  hypervelocity stars (0.13%)
 1  S2's orbital velocity (1.6%)
 5
10
20
30
40
50
60
70
80
90
95
99  ejection jet of Blazars (99.9%)
    ultra high-energy cosmic ray particles (99.99999999999999999999951%)

Angular Velocity

'Orders of magnitude' on Wikipedia

Placeholder

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Defined constants:

  • c - Speed of light in a vacuum. equal to 299792458 $m/s$
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    $\begingroup$ This is great but only concerns a very short range. I think in this SE the range that is needed spans from continental drift to FTL, so maybe a couple more points would be great? just saying that it might be good to expand on this which I think is planned anywas? $\endgroup$ – Raditz_35 Feb 15 '18 at 9:46
  • $\begingroup$ Yeah, it's all in the works. If you feel like a new range is needed, go ahead and either add it to the needed ranges list or make up some new datapoints. $\endgroup$ – Jakob Lovern Feb 15 '18 at 18:37
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Force

Base SI units: $\frac{kg*m}{s^2}$

Common units: N

608.22 N    Amount of force a human of average mass exerts on earth
35,100 kN   Thrust force of Saturn V first stage engine
3.6e22 N    Gravitational attraction between Sun and Earth

Needed ranges:

Lots

Defined Constants: nAn

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  • $\begingroup$ What's the average mass of a human? Are we including babies and the aged? I'd recommend something obvious, like 100Kg. $\endgroup$ – JBH Mar 2 '18 at 3:02
  • $\begingroup$ It's whatever Google says is the average mass. $\endgroup$ – Jakob Lovern Mar 2 '18 at 3:04
  • $\begingroup$ Googling "average human mass" produces numbers between 60Kg and 80Kg. Rather than depending on Google's moving target, please pick one number, state it, and use it. The reference would be much more clear and the result would never change. Google, after all, may return a different number than you used tomorrow, invalidating your comparison. $\endgroup$ – JBH Mar 2 '18 at 3:11
  • $\begingroup$ Honestly, it's just a ballpark number. If you wanna edit the pertinent line in the Mass answer, then update this one to match, that would be immensely appreciated! $\endgroup$ – Jakob Lovern Mar 2 '18 at 3:13
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Mass

Base SI units: $kg$

Common units: kg, g, mg, lb note: lb is actually a unit of force, not a unit of mass. Colloquial usage is only defined on Earth.

'Orders of magnitude (mass)' on Wikipedia

Things you can pick up

kg 
1     a rather heavy stick of butter
76.4  average mass of a woman in the US
88.8  average mass of a man in the US

Modes of transportation

1500    2012 Toyota Camry
5000    African Elephant
1.30e4  Semi-trailer truck
1.74e5  Boeing 747-300
2.97e6  Saturn V

Celestial Bodies (Our solar system)

2.20e14  Halley's comet
9.39e20  Asteroid 1 Ceres (first asteroid discovered. Also largest.)
2.30e21  All asteroids in our Solar System
1.31e22  Pluto
7.35e22  Moon
3.29e23  Mercury
6.39e23  Mars
4.87e24  Venus
5.87e24  Earth
8.68e25  Uranus
1.02e26  Neptune
5.68e26  Saturn
1.90e27  Jupiter
1.99e30  Sun

Celestial Bodies (Not our solar system)

kg
8e30    GRO J0422+32 (a small black hole)
8e36    Sagittarius A* (Milky Way's super massive black hole)
6e42    Milky way
6e51    Observable universe

Subatomic particles

--

  • 9.11e-31 Electron
  • 1.66e-27 Proton and neutron

Defined Constants

Needed ranges:

  • Cellular biology (e.g. mass of various organelles)
  • [In]organic chemistry (e.g. masses of various interesting molecules)
  • Subatomic physics (masses of various bosons and fermions)
  • Weird range where mass and energy get mixed
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