What are the reasons for KSP not using SI units?

[Instresu]

What are the reasons for KSP not using SI units? Is there any mod that changes this? As a student doing lots of calculations it'd be nice to have the correct values without the need to convert them back and forth. And what unit are liquid fuel, oxidizer and electric charge measured in? Tonnes, litres, cubic meters?

By the term "SI unit", I refer to an unit derived from the SI base units:

• metre for length
  
• kilogram for mass
  
• second for time
  
• ampere for electric current
  
• kelvin for temperature
  
• candela for luminous intensity
  
• mole for the amount of substance
  

Kilonewton and the metric tonne is thus not SI units.

[Fel]

kilonewton is just kN kilo-newton...

The metric ton is something else, no idea who thought it was a good idea to have so many conflicting definitions for "ton" though, between the American units, UK, European... it's plain confusing.

I just checked....

Where, in KSP, does it actually provide units of ton? Complaining that the units are in megagrams goes back to kN not being an SI unit.

Edited April 26, 2015 by Fel

[Kosmo-not]

KSP has always used meters for me.

[r_rolo1]

Well, the OP has a point. The temperatures are definitely not in Kelvin, since we have negative ones

[Wallygator]

yes, totally agree: Commonality and standardisation of units of measure should be implemented - full stop.

[problemecium]

Also, I believe a metric ton is just shorthand for a kilo-kilogram / megagram. People have a gut understanding of about how big a "ton" is, but most people haven't ever heard the word "megagram".

[Broax]

Although I completely understand your point I think it would make the game a bit hard to understand for a lot of people.

Personally I think there could be an option for Imperial Units (USA), Metric Units (rest of the world) and the SI (for the more scientific literates). That way everyone would be happy...

[Temeter]

Nobody likes imperial units or kelvin.

[Instresu]

Kilonewton is not a SI unit. The SI unit is newtons; the "kilo" is just a prefix for 1 ∙10³.

[StrandedonEarth]

A metric tonne is 1000kg (~2200lbs), which could be written as Mg. kN is 1000 newtons. A Newton is equivalent to kg(m/s²), so both kN and metric tonne are SI or SI-derived units.

[AbacusWizard]

So multiply by a thousand.

I find that use of kilonewtons and megagrams is fine, because most of the calculations I do involve acceleration as the ratio of force to mass. Kilonewtons divided by megagrams leads to the same result as newtons divided by kilograms, because the thousands cancel out.

[Torham234]

Kilonewton is not a SI unit. The SI unit is newtons; the "kilo" is just a prefix for 1 ∙10³.

So what you are saying is Kilonewton is the same as Kilometer, or a Kilogram. Seems all SI to me...

[henryrasia]

Also, a kilonewton is 1000 kilogram meters per second per second. That sounds metric to me.

I think you just never played a game which used pounds of force, feet for altitude, and feet per minute or knots (nautical mile per hour) for speed. Flight simulators are the worst when it comes to units.

Be thankful SQUAD uses convenient-yet-perfectly-metric units.

[Sandworm]

Switching to standard units would expose too much of the magic that is KSP physics. Start measuring fuel in kilos or liters and people will start wondering why it is too dense. Use accurate temperatures and people will wonder why parts melt so easily. There are lots of little compromises in KSP to facilitate gameplay on such tiny planets. Obfuscation is part of the show.

[rabidninjawombat]

Also, a kilonewton is 1000 kilogram meters per second per second. That sounds metric to me.

I think you just never played a game which used pounds of force, feet for altitude, and feet per minute or knots (nautical mile per hour) for speed. Flight simulators are the worst when it comes to units.

Be thankful SQUAD uses convenient-yet-perfectly-metric units.

Pffft! I want my rocket to weigh 8000 Stone. And to travel 88,000,000 furlongs to the Mun!

[Instresu]

A metric tonne is 1000kg (~2200lbs), which could be written as Mg. kN is 1000 newtons. A Newton is equivalent to kg(m/s²), so both kN and metric tonne are SI or SI-derived units.

I don't agree. From Wikipedia:

The International System of Units (SI) specifies a set of seven base units from which all other SI units of measurement are derived. Each of these other units (SI derived units) can be expressed as a product of (positive or negative, but usually integral) powers of one or more of the base units.

You can't express the prefix "kilo" as a product of the SI base units. "Kilo" is a SI prefix, though.

[Brotoro]

Maybe they did it to see if students could handle trivial powers-of-ten unit conversions.

[Kerano]

So what you are saying is Kilonewton is the same as Kilometer, or a Kilogram. Seems all SI to me...

No - kilograms are SI units, but that's the exception. SI units allow you to do physics calculations using standard formulas without any adjustments. For example:

Work energy = Force * distance

This equation gives Work energy in Joules if you use Newtons for force and meters for distance. If you try to put in distance in kilometers and/or force in kilonewtons, you'll no longer get the correct answer in Joules.

Physics is full of equations like that which are very easy to solve if you stick to SI units, but which won't work if you use non-SI units like kilometers and kilonewtons. (Unless you know what you're doing and adjust both sides of the equation accordingly.)

Edited April 26, 2015 by Kerano

[klesh]

You guys are confusing.

One thing I do know, is that Imperial measurements on a base 12 system are ridiculous and unnecessary. 7/32nds.... GTFO.

0.21 is just so much easier. Its like a holdover from the sliderule days that the old codgers in the US are unwilling to give up.

I wish the big vote on adopting metric would happen again in the US.

[Hobbes Novakoff]

I don't agree. From Wikipedia:

You can't express the prefix "kilo" as a product of the SI base units. "Kilo" is a SI prefix, though.

No, but you can express it as a product of powers of one or more of the base units. Kilonewton = Newton x 10^3.

[Instresu]

No - kilograms are SI units, but that's the exception. SI units allow you to do physics calculations using standard formulas without any adjustments. For example:

Work energy = Force * distance

This equation gives Work energy in Joules if you use Newtons for force and meters for distance. If you try to put in distance in kilometers and/or force in kilonewtons, you'll no longer get the correct answer in Joules.

Physics is full of equations like that which are very easy to solve if you stick to SI units, but which won't work if you use non-SI units like kilometers and kilonewtons.

Finally someone who understands. Yes!

[Hobbes Novakoff]

Also, if we didn't use kilonewton and metric ton (or megagram, but that sounds like some sort of superhero, not a unit of measurement ), what units would we use?

- - - Updated - - -

No - kilograms are SI units, but that's the exception. SI units allow you to do physics calculations using standard formulas without any adjustments. For example:

Work energy = Force * distance

This equation gives Work energy in Joules if you use Newtons for force and meters for distance. If you try to put in distance in kilometers and/or force in kilonewtons, you'll no longer get the correct answer in Joules.

Physics is full of equations like that which are very easy to solve if you stick to SI units, but which won't work if you use non-SI units like kilometers and kilonewtons. (Unless you know what you're doing and adjust both sides of the equation accordingly.)

If you try to put the force in kilonewtons and distance in kilometers, the thousands cancel each other out. Basic pre-algebra stuff.

[magnemoe]

Also, I believe a metric ton is just shorthand for a kilo-kilogram / megagram. People have a gut understanding of about how big a "ton" is, but most people haven't ever heard the word "megagram".

Metric tons are used everywhere in countries who uses the metric system Its not official but everybody uses it of stuff more than 3000 kg and no need for very accurate weights.

[Fel]

Physics is full of equations like that which are very easy to solve if you stick to SI units, but which won't work if you use non-SI units like kilometers and kilonewtons. (Unless you know what you're doing and adjust both sides of the equation accordingly.)

They're prefixes, not units. The difficulty of entering "e3" is zero, the difficulty of reading, with accuracy, a long number of zeros is non-zero.

10000000000

10,000,000,000

10G

Which can you read fastest?

[Radam]

You guys are just trolling. I see something*newtons, meters, m/s, fuel might be presented unitless but its clearly litres.

Is metric allright!