Replies

That one is apparently what happens in a nuclear reaction of the atom bomb kind. The tremendous power of the bomb is due to conversion of a small amount of mass into a lot of energy. That's what they say, anyway.

That is the usual explanation, but that is not quite what Einstein's equation implies. Any change in the energy of a system -- whether it be the result of a nuclear reactions, a chemical reaction, or a cooling breeze -- causes the mass of the system to change. Increase the energy, you increase the mass; decrease the energy, and you decrease the mass. It has nothing to do with nuclear reactions.

Mass is not converted to energy in an atom explosion; it might be more accurate to say that as the energy leaves the system, it carries mass with it.

As far as basic units are concerned, force is thought of as a product of the mass and the rate of change of the speed of the object. And then speed is a product of space and time. We're not real clear on what time might be, and why it is considered a dimension like height, width, and depth. It gets worse. We say space is 3-dimensional, but it is treated as 4-dimensional when they consider time, and now physicists are thinking in terms of more dimensions, 11 maybe. I don't know, I'm still open to suggestion.

Two points here:

1. Force is a derived unit in the SI units; however, in the so-called "English Engineering" system, force is a fundamental quantity. As a result, we end up using "pounds" to refer both to force (lbf) and to mass (lbm). (I prefer SI units.)

2. It seems to me that time is taken as a fundamental dimension because it is a basic or axiomatic concept. It is hard for me to imagine explaining time in terms of something simpler. (But like you, I'm still open to suggestion.)

"It seems to me that time is taken as a fundamental dimension because it is a basic or axiomatic concept. It is hard for me to imagine explaining time in terms of something simpler."

I still remember my head throbbing the first time I saw "natural units." In that system, Planck's constant & the speed of light are unitless and everything else's unit is expressed as a fractional exponent. Never did really understand it -- I just did it.

we end up using "pounds" to refer both to force (lbf) and to mass (lbm).

In physics class they forced us to use the term "poundal". That is the one improvement I will acknowlege the SI metric system made. We don't have to use poundals anymore, although some still do [probably at some NASA Mars contractor's facility.]

I will have to insist that during the explosion of an atom bomb, or the operation of a nuclear fission plant, some mass is irreversibly converted to energy but this does not occur in chemical reactions.