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Kilogram is now officially defined in terms of the mass of C-12. ....
Why bother to talk about ions, isotopes, atomic clocks and Avagodro
too early? This can only reinforce the feeling that "physics is not
comprehensible". What is gained [from explaining new definitions of
SI standards to those who are starting to learn physics]?
The same goes for using 4186 J/(kg*K) instead of 1 cal/(g*C), for water,
when we start teaching calorimetry. How can you explain Joule's paddle
experiment without calorimetry? How can you explain 4186 without a
reference to an experiment with which students are not yet familiar?
And how can you make them familiar with the experiment if they do not
know that the amount of internal energy, lost or received ("heat"),
can be measured.
My personal preference is to begin with calories and switch to joules
later. This approach protects me from explaining today's topics in
terms of what they will learn tomorrow. ....