I A model of what makes up the physical world

[pkc111]

One need I have for a simple mind map showing the fundamentals, is when a student asks (as happened last year) , what is momentum. My response was mass x velocity. The student's response was "yes, but what is it really?".
This was after they had developed some really nice understandings of matter and energy and the differences between them, we had understood motion well in terms of its descriptors of speed, velocity, acceleration and up to that point physics made sense to them. Thats where I got stumped..I didnt have a nice description of what it was that had meaning to the students and related it to the real world. I told them it is "an indicator of the difficulty to stop of an object, but really kinetic energy is a better indicator of it". I could see it wasnt really a satisfactory answer to the student.
In hindsight I felt I really needed a map, and be able to point to a box of these less tangible physics words and say they belong here in the world of " mathematical constructs" so don't worry too much about their meaning or relationship to the world just at the moment... just use it and be thankful that it is conserved in collisions.. so you can solve some of these great problems!
I don't want a map for students to recite and learn and spend hours in talking about it, I want it to show what can be "understood" easily..in terms of some specific simple relationships.. and also list those which don't really have a place that is easy to see, and really don't need to be understood beyond a mathematical formula for the syllabus at this point in time...and the real value of it is in its usefulness rather than its meaning.
I want a map to smooth the journey for the students so they don't get caught up with concepts they don't feel they understand and therefore worry they are missing something in the course (and feel reassured that many other scientists don't fully understand the concept either). But for this concepts for which there is some sort of classical model for understanding (mass, energy, space, time, force, fields) I want to be able to have one...at least in my own mind.

 

[PeterDonis]

a student asks (as happened last year) , what is momentum. My response was mass x velocity. The student's response was "yes, but what is it really?".

There are two ways of handling this. One would be to disuss the relationship between momentum and space translation symmetry, given by Noether's Theorem, which is more generalizable than mass x velocity. (For one thing, momentum = mass x velocity is no longer true in relativity.)

The other, which you'll eventually be forced to in any case, is that we don't know what momentum "really" is; we don't know what energy "really" is; we don't know what mass "really" is; etc. All we know is that we observe certain law-like regularities in the way the world works, and these things like "momentum", "energy", "mass", etc. appear in the mathematical models we construct to describe these law-like regularities and make predictions using them. If the student wants more than that, they need to look elsewhere than science class; as Indiana Jones told his students, "if it's Truth you're interested in, Dr. Tyree's philosophy class is right down the hall."

 

[Mark44]

The other, which you'll eventually be forced to in any case, is that we don't know what momentum "really" is; we don't know what energy "really" is; we don't know what mass "really" is; etc.

This put me in mind of one of the Feynman Youtube videos, on magnets, and why they repel each other, but more about how difficult "why" questions are in physics.

 

[sophiecentaur]

I don't want a map for students to recite and learn and spend hours in talking about it,

An admirable sentiment. But what audience are you actually going to present this map to? I am in UK and the school divisions are slightly different. I have read that High School is for students from 14 to 18. In the UK, 'secondary' is from 11 to 16 and then there is a two year '6th Form' which is aimed at preparing for University Education. The Physics Syllabus (called a specification, these days, I think) is chock full of stuff that they need to learn and they are as grateful as hell if you can give them a practical way through. A concept map of the Hyperphysics kind is something that's very tangible and it's at a low philosophical level but highly applicable for them. It shows them categories of study and it's a 2D tick box for them to see their progress. I know it has its shortcomings but, if you want all students to have some idea about what a map is all about then they all have a chance with it.
Bottom line is that most of the comments people have made in this thread are way above the heads of the majority of School age students in respect of words and concepts. The map classifications that have been discussed are suitable for adult retrospection and they are not for finding your way through for the first time.
Dealing with the "what is x, really" question is a separate problem.

 

[PeterDonis]

Moderator's note: two off topic posts have been deleted. Please keep the discussion on topic.

 

[pkc111]

The other, which you'll eventually be forced to in any case, is that we don't know what momentum "really" is; we don't know what energy "really" is; we don't know what mass "really" is; etc. All we know is that we observe certain law-like regularities in the way the world works, and these things like "momentum", "energy", "mass", etc. appear in the mathematical models we construct to describe these law-like regularities and make predictions using them. If the student wants more than that, they need to look elsewhere than science class; as Indiana Jones told his students, "if it's Truth you're interested in, Dr. Tyree's philosophy class is right down the hall."

Yes I like this approach of being clear about what science is and what it is not...which reminds me that I should try to prepare students minds for Physics before I teach it... manage expectations so to speak. I think I need to let them know that mathematics is a valid language, just as valid as words, and it is sometimes the only accurate way we have to describe a concept. In some ways as Feynman says in the magnetism video it would be cheating the student to try and explain some concepts in any other way.
There is a subject called Theory of Knowledge in the IB program which has a resource which may give me a good basis to do that I feel (see below).

 

[Dale]

My response was mass x velocity. The student's response was "yes, but what is it really?".

I would strongly recommend to never ever engage in such a question. Simply repeat the definition. The definition is the answer to the question “what is it” and it is also the answer to the question “what is it really” and the question “what is it really actually truly”.

Alternatively, you can restate the definition and then say something like “but what you should be asking is why is it useful”

 

[sophiecentaur]

I would strongly recommend to never ever engage in such a question. Simply repeat the definition. The definition is the answer to the question “what is it” and it is also the answer to the question “what is it really” and the question “what is it really actually truly”.
Alternatively, you can restate the definition and then say something like “but what you should be asking is why is it useful”

Non - Scientists are the ones who tend to justify the "why' question. Getting across the idea to students that Physics only tries to make working models of the World can relieve the stress they can feel about not 'understanding things fully'. They have to learn that Science does not work on Axioms, like Maths does. We are aiming at a set of theories that are mutually self consistent, rather than any ultimate truth.

 

[pkc111]

so from a classical physics point of view if we decide to relegate momentum to only being talked about as concept or mathematical construct rather than some sort of thing like matter or energy, then is it valid to ever describe momentum as being "transferred" during a collision?

 

[weirdoguy]

if we decide to relegate momentum to only being talked about as concept or mathematical construct rather than some sort of thing like matter or energy

Energy is a property of matter/fields and a mathematical construct the same way momentum is.

 

[Dale]

We are aiming at a set of theories that are mutually self consistent, rather than any ultimate truth

Self consistent and consistent with experimental evidence.

 

[Dale]

if we decide to relegate momentum to only being talked about as concept or mathematical construct rather than some sort of thing like matter or energy

I would not do that at all! Momentum is on the exact same footing as energy. Neither is a “thing”.

 

[Vanadium 50]

To build on Dale's point (and "what is it really?" has the inevitable follow-up, "yeah but what is it really really?") Which is the better answer?

"Momentum is a quantity that was discovered to be useful".
"Momentum is here on the map, next to Ohio"

 

[pkc111]

I would not do that at all! Momentum is on the exact same footing as energy. Neither is a “thing”.

Ok so I am guessing you would not describe momentum or energy as being "transferred" ...in the everyday meaning of the word? I mean concepts don't usually "transfer' right?
Btw I only want to understand the classical model of the world first. As I hope it is has definitions and descriptions that are going to be consistent and create some sort of model that hangs together.
so are you describing momentum and energy on the same footing... as only mathematical constructs ...the way that classical physicists would have thought of them?

 

[Dale]

Ok so I am guessing you would not describe momentum or energy as being "transferred" ...in the everyday meaning of the word? I mean concepts don't usually "transfer' right?

Why not? That is the basis for the majority of our monetary system at the present. The funds that my employer transfers are not physical things. Why should only “things” be transferable? I have also transferred knowledge to my students and traits to my children.

so are you describing momentum and energy on the same footing... as only mathematical constructs ...the way that classical physicists would have thought of them?

I wouldn’t describe them that way. I would never say “only mathematical constructs”. It is only your insistence on making this map where you artificially label some terms as parts of the “classical view of the universe” and others as “calculated quantities” that forces such a dichotomous characterization.

Look, this is clearly a doomed venture. Your map is not even helping you understand anything. How will it possibly help your students? At this point all we can do is recommend against it.

 

[pkc111]

Why not? That is the basis for the majority of our monetary system at the present. The funds that my employer transfers are not physical things. Why should only “things” be transferable? I have also transferred knowledge to my students and traits to my children.

Look, this is clearly a doomed venture. Your map is not even helping you understand anything. How will it possibly help your students? At this point all we can do is recommend against it.

To say that the whole universe is just mathematical concepts may be true at a higher level, however it is not the framework of the high school syllabus I teach or the textbooks that students have and it's not an model that allows access to understanding to most 17 year olds.
I also can't see how it was the entire framework of classical physics either which is often described as having a "mechanical universe" paradigm.
I also don't think it's unreasonable, or "doomed", to ask what was the model of the universe ...Definitions of concepts, their nature, and most importantly to me their relationships to each other (hence the aim of a mind map) of mass energy momentum forces fields torque...that was held by the mainstream thinkers around 1900..About their mechanical universe.

 

[Dale]

To say that the whole universe is just mathematical concepts

I wouldn’t say that. I wouldn’t even say that about momentum and energy, let alone the whole universe. This “mathematical concepts” stuff is a product of your map, and one indication why it is a bad idea.

I also don't think it's unreasonable, or "doomed", to ask what was the model of the universe

It is not doomed to ask what is the model of the universe, that is what physics is. What is doomed is your map. It introduces a bunch of classifications that are not part of the model. You are trying to say that these parts of the model are more fundamental or more real than other parts, and the model itself does not make that distinction.

Definitions of concepts, their nature, and most importantly to me their relationships to each other

Then use the hyperphysics site. It does exactly that, complete with text describing many of the relationships.

 

[sophiecentaur]

so from a classical physics point of view if we decide to relegate momentum to only being talked about as concept or mathematical construct rather than some sort of thing like matter or energy, then is it valid to ever describe momentum as being "transferred" during a collision?

Energy is a property of matter/fields and a mathematical construct the same way momentum is.

Both of those posts are factually correct and well written and I agree with them. But seriously, how do they fit in a thread about presenting Physics to a mainstream class of immature students who may not have yet even got the SUVAT equations sorted in their minds?
Many classes will have one or two students who can cope with this sort of thing but they will be future PF stalwarts and they've already got the basics. I think that many of the contributors to this thread have forgotten just how little they had in their heads before they started on their revision for the Physics exams.
I have often told students, unashamedly, that it's a trick that delivers answers. Never had any complaints about that.

 

[Herman Trivilino]

I have decided to aim for a simple classical physics view of the universe and a modern view of the universe separately...as they really are fundamentally different paradigms I now realize probably never meant to be put together.

It's a requirement that they fit together. They are not separate, one is a part of the other.

so from a classical physics point of view if we decide to relegate momentum to only being talked about as concept or mathematical construct rather than some sort of thing like matter or energy, then is it valid to ever describe momentum as being "transferred" during a collision?

Momentum and energy are in the same category. They are inventions of the human intellect. Matter is not in that category.

And there is no need to insert the restriction concerning classical physics.

The reason we ask students to learn about momentum or any of the concepts of physics is because we have discovered their utility. That is, they are useful for understanding how Nature behaves. There are lots of other concepts designed to help us understand Nature that we don't ask them to learn because they are not as useful.

 

[pkc111]

So is it accurate for a physicist to describe energy as being "absorbed" by an object? Given that it doesn't exist.
I mean I can go along with the idea of talking about it from a bookeeping sense as being "transferred" as non existent money is "transferred" between bank accounts, is "absorbed" being used in a similar way?
Cos eventually you talk about them literally the same way as you do existent material (which are not concepts) (eg flow,absorbed,transferred), and then at the same time you remember they don't exist..All except matter ...which does exist...is that the idea?

 

[Dale]

Given that it doesn't exist.

You can measure it. It seems weird to think that you can measure something that doesn’t exist. Certainly I wouldn’t claim that it is non existent and I think such a claim is hard to justify.

 

[pkc111]

It's a requirement that they fit together. They are not separate, one is a part of the other.

.

Why is it a requirement of any 2 paradigms that they fit together?
Educational theory is full of separate theories/ paradigms...cognitive theories, behavioural, cognitive/behavioural theories and a whole myriad of others etc, but they don't combine into one. They do not fit together at all, they are different lenses to attempt to explain the same thing, but they don't always combine very nicely in rational minds...they are very different views whose value is that they are internally consistent, but come with no guarantee that they are going to join well with another theory... imo.
eg How can the idea that space and time as different entities (Newtonian paradigm) fit with an Einsteinian paradigm of them being part of the same thing? I can't see how one single model can say both of these things at the same time and be internally consistent ?

 

[pkc111]

Ok so this is the words my oxford dictionary of physics uses to describe some key physics terms and probably my reference for describing physics terms to 17 year old kids..

Space: a "property" of the universe...
Time: a "dimension"...
Force: an "agency"...
Energy: a "measure" of the ability...
Momentum: the "product of mass x velocity of a body"... I guess this is the same as saying " a measure of"
Matter: a "substance" that takes up space and has mass
Torque: the "product" of a force and a perpendicular distance .. I guess this is the same as saying " a measure of"

I trust the wording of these definitions are internally consistent with the accepted mainstream framework of physics concepts and will place some foundations of understanding for a smooth studying of physics at higher levels

And so the questions from students are obviously going to be things like:
how can a "measurement" transfer or absorb...my future answer...it just does...like money on balance sheets.
how do you travel through a "property" (ie space)...um...you just do
are any of these things real?...my future answer...ask your philosophy teacher.
do any of these things "exist"...my future answer...define exist...you can say matter does...some people say energy does some say it doesnt...ie go and ask your philosophy teacher what exist means and come back.
yes I know that p = mv but what is momentum really?...my future answer...no one knows the true nature of these things (see Feynman interviews)

Of course any suggestions on improvements to my responses are welcome!

 

[Dale]

You will be much better off using a standard physics textbook instead of the Oxford dictionary. Very often the technical definitions are different from the common English definitions. Once you have good definitions, then stick with them.

If you are teaching your physics class so that they ask questions about whether something exists or not then you are doing something wrong. Nobody ever asked that in any of my physics classes. We were too busy learning how to use the models and prepare for the exam to waste time like that.

 

[pkc111]

You will be much better off using a standard physics textbook instead of the Oxford dictionary. Very often the technical definitions are different from the common English definitions. Once you have good definitions, then stick with them.

If you are teaching your physics class so that they ask questions about whether something exists or not then you are doing something wrong. Nobody ever asked that in any of my physics classes. We were too busy learning how to use the models and prepare for the exam to waste time like that.

OK i don't know what sort of school you teach in but at our school we really try to foster a spirit of enquiry from kids in science, and the kids do. I don't have a problem at all with kids asking these questions...to me its a very healthy sign . The trick as I see it as a teacher is giving them a quick and satisfying answer (thats not incorrect) to allow them to happily get on with the real work I want them to ie problem solving.

 

[pkc111]

You will be much better off using a standard physics textbook instead of the Oxford dictionary. Very often the technical definitions are different from the common English definitions. Once you have good definitions, then stick with them.

If you are teaching your physics class so that they ask questions about whether something exists or not then you are doing something wrong. Nobody ever asked that in any of my physics classes. We were too busy learning how to use the models and prepare for the exam to waste time like that.

The dictionary I am using is the Oxford dictionary of Physics (latest edition), not a general dictionary.
Are you saying that a physics textbook would be a better supply of definitions than this? OK i will look for a first year uni one.

 

[Dale]

The dictionary I am using is the Oxford dictionary of Physics (latest edition)

Hmm, I am surprised that the definitions are so bad then.

OK i don't know what sort of school you teach in but at our school we really try to foster a spirit of enquiry from kids in science,

We had plenty of questions from the students, but just none of the philosophical sort you are describing. Not all questions are a good sign. Only good questions are a good sign.

I don't have a problem at all with kids asking these questions...to me its a very healthy sign .

The question “what is momentum really” is a bad sign, not a healthy one, IMO. It means that they don’t even understand that the purpose of a definition is to answer that question.

It also means that they are uncomfortable with the idea, that they believe that you are tricking them or lying to them. It indicates that they feel that you are not already telling them what it really is.

 

[pkc111]

Hmm, I am surprised that the definitions are so bad then.

The question “what is momentum really” is a bad sign, not a healthy one. It means that they don’t even understand that the purpose of a definition is to answer that question.

It also means that they are uncomfortable with the idea, that they believe that you are tricking them or lying to them. It indicates that they feel that you are not already telling them what it really is.

Ok well I am not sure what sort of enquiry you foster in your classroom and what sort of depth of thinking you allow from your students, but if you are happy to stifle it by labelling it as unhealthy then that's up to you I guess.
I think it is quite natural for kids and us all to seek meaning and deeper understanding and actually think I have a duty to encourage it, and I can see why p=mv would seek further questions about what is it really? The fact that you know there is know known answer beyond that makes it very easy to say they should be happy with the explanation they first get and not want a deeper explanation.

 

[pkc111]

Hmm, I am surprised that the definitions are so bad then.
.

Well if you don't believe me you may wish to have a look yourself. and if you have some better words to start the definition of each then you may wish to share them? rather than just dissing...

 

[Herman Trivilino]

Why is it a requirement of any 2 paradigms that they fit together?

I was responding to this comment:

a simple classical physics view of the universe and a modern view of the universe separately...as they really are fundamentally different paradigms I now realize probably never meant to be put together.

Modern physics is the more general of the two, so it must match classical physics within the appropriate limits of validity. See the example I give below.

How can the idea that space and time as different entities (Newtonian paradigm) fit with an Einsteinian paradigm of them being part of the same thing?

When speeds are small enough and gravity weak enough both Newtonian and einsteinian physics provide matching results.

 

[sophiecentaur]

We had plenty of questions from the students, but just none of the philosophical sort you are describing. Not all questions are a good sign. Only good questions are a good sign.

Ok well I am not sure what sort of enquiry you foster in your classroom and what sort of depth of thinking you allow from your students, but if you are happy to stifle it by labelling it as unhealthy then that's up to you I guess.

A Straw Man argument, I'm afraid. The reason that teachers are paid to teach is to enable most of their students to get high enough grades to progress to the next stage of education. That's how Schools and their staff are assessed by Ofsted (or non-UK equivalents). If a teacher is prepared for lots of extra-curricular contact with an elite band of students (who are also prepared), the sort of thing @pkc111 is recommending could be very useful.
A fellow student of mine at University was totally in love with his Physics. He read around it constantly and produced good written assignments during the course. He was our go-to source for help with our assignments. However, he just didn't LEARN enough to do well in the Finals. He got a Third Class Hons., which shocked us all. There was no way he could get into a post grad course without spending / wasting a lot more time at first degree level. It was a shame that his tutors didn't spot the signs and get him targeted properly.
I don't agree with much of the content of subject specifications but I do notice that, beneath the flowery language about developing the Scientific Mind etc. etc. there's a basis of needing to know content.

 

[Vanadium 50]

@pkc111, do you mind telling us your physics background and how long you have been teaching?

 

[pkc111]

@pkc111, do you mind telling us your physics background and how long you have been teaching?

The thread is not about me. Probably best to stick to the topic Id say.

 

[weirdoguy]

Well, partly it is about you because YOU are trying to make some things up for students, that won't really help them.

 

[pkc111]

bit of a stretch of the relevance there I think

 

[DrClaude]

Thread closed for moderation.

Edit: after some brief discussion the mentors have decided to keep this thread closed. It had gotten a little heated.