Is it kilograms or grams?

[Lightium]

I am reading these note's on MIT open courseware and I don't know if m is in Kg or g.
On page five it gives the exit velocity, but doesn't say what m is and I know it's the mass, but in kilograms or grams?

https://ocw.mit.edu/courses/16-522-...5cdb7d89c3585a3_MIT16_522S15_Lecture10-11.pdf

 

[Lightium]

I feel silly.

"The SI base unit of mass is the kilogram (kg)."

Mass - Wikipedia

en.wikipedia.org

 

[Nigel Goodwin]

I feel silly.

"The SI base unit of mass is the kilogram (kg)."

Mass - Wikipedia

en.wikipedia.org

Why? - they are the same thing, personally I would suggest the gram is the base unit - as a KILOgram is just 1000 grams. Just as ohm is the base unit of resistance, and not the kilo-ohm, mega-ohm, or anything else.

I've not read the PDF, but if it doesn't specify what the units are it's a VERY poorly written document. I suppose it could be obvious from the context, and the value, but it's still sloppy not specifying the units - and it would no doubt be marked down for such an omission.

 

[Pommie]

SI units are very specific and mass is always in Kg. Except when ........

Mike.

 

[jpanhalt]

I've not read the PDF, but if it doesn't specify what the units are it's a VERY poorly written document. I suppose it could be obvious from the context, and the value, but it's still sloppy not specifying the units - and it would no doubt be marked down for such an omission.

It is a theoretical paper in physics. Einstein's original paper on E = mc^2 didn't include units either. Here's a link to a translated copy: https://cdn2.hubspot.net/hubfs/232514/Einstein E=mc2 (pp172-174).pdf . Failing to do so does not make it poorly written.

Omitting units is very common, unless specific examples are given, because they don't matter to the relationships so long as one is consistent. The result, of course, will be in the units system one chooses. We were taught to solve such equations looking only at the units. That is, "solve for the units. "

 

[Tony Stewart]

CGS dates back to Gauss and Maxwell using grams, and are mainly scaling differences and still used in rare instances such as Particle Physics.
ref: https://www.wikiwand.com/en/Centimetre–gram–second_system_of_units

 

[Nigel Goodwin]

SI units are very specific and mass is always in Kg. Except when ........

Mike.

Regardless, the base is still the gram - kilogram (as you obviously know) refers to grams times ten to the power of three.

Capacitors are mainly specified in uF, nF and pF - but their base is still the farad - and who ever uses a 'Bel'?, but the decibel is a tenth of a Bel.

 

[Lightium]

Thanks to everyone for your help.

 

[Pommie]

Omitting units is very common, unless specific examples are given, because they don't matter to the relationships so long as one is consistent.

A bit like the specific heat of water is stated as 4.2 and units can be either J/g K° or kJ/kg K° or any multiplier you wish.

Is Kelvin or Celsius the SI unit of temperature?

Mike.

 

[Lightium]

Is Kelvin or Celsius the SI unit of temperature?

It's Kelvin.

SI Units

www.nist.gov