My god! 1 cal = ?? J
 

In the famous Thermodynamics book of Moran and SHapiro,

1 cal = 4.1868 J

Searched google:

1 cal = 4.1868 J (1860 times) 1 cal = 4.184 J (9780 times)

Which one is more accurate??

I was so surprised that there are discrepency in such a very classical and standard unit factor.

Thanks.

Re: My god! 1 cal = ?? J
 

The issue comes from what is the definition of a "calorie".

1 cal = 4.184 J is for a "thermochemical" calorie, the definition used in the U.S.

1 cal = 4.1868 J is the calories as defined by ISO.

There are other units that have multiple definitions (pounds troy vs. pounds avoirdupois, e.g.).

Source: Engineering Unit Conversions, by M.R. Lindenburg.

Re: My god! 1 cal = ?? J
 

If you're that concerned, perhaps stick with the ISO definition (4.1868 J).

Or just do everything in SI units to start with....

Re: My god! 1 cal = ?? J
 

Interesting to note, I must say.

Re: My god! 1 cal = ?? J
 

Thanks for the info.