Physics Lecture

I had this lecture sometime ago and I spotted two interesting things.
1) The lecturer was explaining about science and how it is about the cycle of hypothesis, theory and experiment. That was all fine and well, but then the example he gave really made me straighten up in my seat. You see, he was giving an example about hypothesis:
"So, let's say we have hypothesis about speed; that it is distance over time. We test it, and the experiment agrees, so we have a theory that speed is distance over time."
The fatal mistake here is that speed is a concept that we devised to substantiate the notion of rate of change of distance. Speed is by definition distance over time; it is self-contained truth that is indisputable.
To be fair, the lecturer has that 'things that I regret almost as soon as I said it' look. He realised his fatal mistake but went on without rectifying it to avoid confusion.
2) The lecturer has this interesting quiz: "Is this true or false: an object with non-zero acceleration can never stop and stay stopped."
Again, the key lies with definition. Since the object's movement is already defined as non-stationary (non-zero acceleration), of course it can never stop, neither can it stay stopped. So is there a point of asking the question, unless it is epistemology class and/or the absurdity is intended?

Oh well.

person, persons, people, peoples

"I saw three person," said he, pointing at the picture.
My student was describing a picture. A cooking class.
"Three people, you mean," I interrupted.
"Oh yeah, three people," he corrected himself.
"Well should you have said 'three persons' it may not be so fatal an error," I mutterred.
"What do you mean?" he asked.
Oh well, we can use a little detour.
"There are such things as 'persons' and 'peoples'." I sipped my coffee.
His eyes grew wider and confusion was there, peeping from the corner, staring.
"But that doesn't makes sense," he protested.
Every English teacher is, of course, well-aware of such statements. After all, we used to wonder about that too -- How language doesn't make sense, but apparently we have come to accept it. Language is like a slithering snake. It is constantly moving. It is stubborn in having its own way. It cannot be contained by rigid rules.
So with the smile of the enlightened I replied, "It's like that."
"Let's start with 'peoples'. There is another meaning of 'people'. It is referring to the citizens in a nation collectively. A nation has a land and a people." And perhaps a corrupt government, too, I added inaudibly. Citizenry is a good synonym, but let's leave it at that.
"I see. But what about 'persons'?"
"Well, it is the plural form of 'person'," I smirked, anticipating the bewilderment that is now visible.
"'People'," I continued before he uttered a word. "is a collective term. It emphasises on the group as a whole. 'Persons' is not used very often. Well, it is a plural form, but here we emphasise on the individuality of each member of this group we are talking about."
I let out a pause for impact.
"A good example would be the Trinity," I continued. "We usually say Three Persons of Trinity. We want to emphasise that there are three entities we are talking about."
Of course, only one noun has this special case. Which other nouns have to be emphasised on their individuality? Which other nouns resist grouping as a whole and insist separateness? Which other nouns are so selfish, revolving around themselves? Anthropocentrism does invade every area of knowledge, sadly.
"Teacher, can I continue my description?"
I awoke from my mental discourse.
"Yes, please."