Why the SI-unit for mass is chosen to kg and not g?

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In summary: The SI system has an "A" unit for electric current, "C" for electric charge, "V" for voltage, "W" for watt, and so on.
  • #1
EL
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Anyone who knows why the SI-unit for mass is chosen to kg and not g?
 
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  • #3
The link says: "The kilogram is the unit of mass; it is equal to the mass of the international prototype of the kilogram."

Yes but why wasn't it defined as: "The gram is the unit of mass; one kilogram is equal to the mass of the international prototype of the kilogram, "
Why was that ugly prefix k kept?
 
  • #4
Actually, the way I learned it, there were two standard systems- cgs for "centimeter- gram- second" and mks for "meter- kilogram- second". If you are working with "normal" sizes then mks is natural- a gram is awfully small (about the mass of a raisin!). That's why there are often two names for particular measurements: in mks, the unit of force is the Newton (which will accelerate a mass of one kilogram at one meter per second per second) and the unit of energy is the Joule (the work done in applying a one Newton force for a distance of one meter); in cgs, the dyne (which will accelerate a mass of one gram at one centimeter per second per second-and is really small weak) and the erg (the work done in applying a one dyne force for a distance of one centimeter- now that's almost non-existant!).

It's the fact that most measurements are in the mks range rather than the cgs range that make mks (and therefore the kilogram) the standard.
 
  • #5
Ok, thanks. But I still don't like it... :smile:
 
  • #6
HallsofIvy said:
erg
I think I know why they have chosen the kms system...this just sounds like you had a fishbone in your throat :yuck:
 
  • #7
Maybe it was just a case of one standards decision following after another. The original "gram" was handy because a cubic centimeter of liquid water near the ice point weighs about that much. The "cgs" system was quite suitable for ordinary chemistry experiments; it grew more unwieldy when considering larger things (industrial and astronomical). Maybe they should have invented another name, for example, a "pond" for 1,000 grams and proposed a "mps" system. But gram was already established, much data recorded in that unit (and multiples like km) and conversion was an easy slide of decimal point three digits leftward. So, "mks" it became.

P.S. I have in mind that "pond" would mean a unit of "ponderable" mass.

P.S. Units for electromagnetism also complicate the story.
 

1. Why is the SI-unit for mass chosen to be kg?

The SI-unit for mass, or kilogram (kg), was chosen because it is a more practical and convenient unit for everyday use. It is larger than the gram (g) and allows for easier measurement of larger objects without using decimals.

2. Can't we just use grams as the SI-unit for mass?

While grams (g) are commonly used for measuring small masses, using kilogram (kg) as the SI-unit for mass allows for a more consistent and standardized system of measurement across different fields of science.

3. How was the kilogram (kg) defined as the SI-unit for mass?

The kilogram (kg) was originally defined as the mass of 1 liter of water at its freezing point in 1795. However, in 1889, it was redefined as the mass of a specific platinum-iridium alloy cylinder known as the International Prototype Kilogram (IPK), which is still used as the standard today.

4. Why not use a different unit, such as the pound or ounce, for mass measurement?

The use of the kilogram (kg) as the SI-unit for mass allows for a more universally understood and consistent system of measurement, as the pound and ounce are not commonly used in scientific contexts. Additionally, the kilogram is a more precise unit of measurement compared to the pound and ounce.

5. Does the choice of SI-unit for mass affect calculations and measurements in science?

Yes, the choice of SI-unit for mass can greatly impact calculations and measurements in science. The kilogram (kg) is a base unit in the SI system and is used in many formulas and equations in fields such as physics and chemistry. Using a different unit could result in errors or inconsistencies in these calculations and measurements.

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