I think Tony's "some pattern [of 'wobbles'] that happens further away and/or later than it does here and now" was exactly what I was trying to catch in my slogan of "do like me - but later", trying to bring in imagined action to make it more concrete. (Also created as an interactive diagram - ending up with https://slowthinkingphysics.net/WvMultiMimicrySineUpDownLongIRE – Videos of lines of long-passed-on student waving their arms about did not seem appropriate...).
And I think there is an issue with interpreting what gets displayed on a cro. A suggestion, perhaps particularly when supporting colleagues whose specialism is not physics is to avoid or limit the use of the cro(http://supportingphysicsteaching.net/So02TLnugget07.html, but there are more positive suggestions here – https://eric.ed.gov/?id=EJ775652). Maybe the cro display is so potentially confusing that it is best avoided until the cro becomes a tool for students to measure with?
And anyone have a good suggestion for Gary about how to show traveling sound waves in a medium, or a convincing story/sequence of demonastrations that make it seem strongly "more than likely'?
I think there is a mismatch between the Cartesian graph and what we are keen that other should understand . James - I'd blame the tools and not the wielder of the tools. Came across this today, which seems to 'fit' the lack of fit....
"Like all the best formalisms his diagrams avoided the need for thought. They had a structure that naturally implied where the next pieces had to fit. If you want to know what comes next.
as Feynman put it, ‘it’s like asking a centipede which leg comes after the other’."
Barrow: Cosmic imagery, p.504.
He was writing about Feynman diagrams, but here also I just would not start with the graphs - experiences with deciphering exam questions about snapshots fed into the sequence suggested in IRE01.
We need the exam board answer [transfer of matter without transfer of energy...]but perhaps something to help them get their heads around the concept. I have been moved by:
'some pattern [of 'wobbles'] that happens further away and/or later than it does here and now'. This certainly helped me with the idea of gravitational waves and it sort of caters for Mexican [crowd] Waves.
2. How can waves be represented?
(a) The diagram that lets us 'see' wavelength - A SNAPSHOT
Represented be a photograph of a wave [slinky or Rubens tube] at one instant
(b) The diagram that lets us 'see' period - A SHORT STORY or BIOGRAPHY of one particle or point.
Represented by some form of CRO or picoscope trace.
The big problem here, of course, is that the sinusiodal images look the same and students want to ascribe wavelength to the second diagram
(c) [And this probably doesn't apply at 11-16] An indication of the various frequencies/wavelengths that are present in a complex signal. Represented by a frequency spectrum [graphics equalizer?] or manifested by using a diffraction grating [especially for a line spectrum]
Only then can we go on to explain the behaviour of waves [no diffraction/interference in GCSE?] utility of waves and their fitness for purpose [ultrasound, X-rays, etc.].
On the whole snapshot line of discussion. I’m a fan of Randall Knights Five easy lessons and there is lots in the book I really love. When I first got the book, it was the first time I’d seen someone really try and pick apart a way of teaching – what a wave is doing and what the particles in a wave ate doing in a really structured way.
He suggests teaching ‘snapshot graphs’ showing displacement vs position at a point in time and ‘history graphs’ showing displacement vs time at a position in space. And then these together as a pair offer a way of representing the wave. It all seemed to make sense and I spent a while working through it all. I then ran a session for teachers and it just was a disaster, providing more confusion that help. One teacher commented “James you seem to have to tried to offer a solution to a problem that I didn’t think I had and still don’t and all you solution has done is confuse and upset me”. I can see how we need to separate the movement of the wave propagating ‘thing’ from the wave itself and this is key, but each time I’ve returned to Knight’s suggestion I’ve never really made much progress myself or with other teachers.
I cannot find an easy way to add images but on page 158/159 if you have the book you’ll see what he suggests, which I’m just not convinced by. Seems the effort:reward ratio doesn’t work in favour of the teacher or learner.
In the end I got a slinky and/or rope. Wobbled it and then tied a ribbon on to a point and then cued people in to look at that – seemed to do all I needed to separate the wave/oscillator.
The idea of "snapshots" is very powerful and I wonder if it's far more accessible now we have so many cheap cameras. We can do snapshots - where we have a set of physical descriptors that relate to a moment in time. But we can also do videos - where we have patterns in changes and relationships between physical descriptors.
The newsletter made me think about how we start with waves and some of the teaching limitations. One obvious one is teaching that "sound" is a wave. This is tricky because we are very good at hearing - if we were any better we'd hear thermal noise. So we can hear things that are very small effects. Thinking about the source - medium - detector model, being able to show that sound passes through the medium as a wave would be very nice. Except I can't think how we do it, especially given the comment I already made. So we could resort to showing that the source acts in a wavelike way, and likewise with the detector. That then leaves the medium acting in the same way as being quite probable, with a bit more evidence later in the form of Kundts tube. Does a Rubens Tube supply more evidence? I'd like to be convinced but I'm not. You can see sound here: https://www.youtube.com/watch?v=px3oVGXr4mo but it doesn't look that wave like and it's rather complicated to understand what you're looking at. It could be presented as evidence from authority, backed up by some socially constructed knowledge. But I think showing sounds travels as a wave in a medium is quite difficult and possibly a limiting concept?
Thank you both for kicking off this conversation.
I think Tony's "some pattern [of 'wobbles'] that happens further away and/or later than it does here and now" was exactly what I was trying to catch in my slogan of "do like me - but later", trying to bring in imagined action to make it more concrete. (Also created as an interactive diagram - ending up with https://slowthinkingphysics.net/WvMultiMimicrySineUpDownLongIRE – Videos of lines of long-passed-on student waving their arms about did not seem appropriate...).
And I think there is an issue with interpreting what gets displayed on a cro. A suggestion, perhaps particularly when supporting colleagues whose specialism is not physics is to avoid or limit the use of the cro(http://supportingphysicsteaching.net/So02TLnugget07.html, but there are more positive suggestions here – https://eric.ed.gov/?id=EJ775652). Maybe the cro display is so potentially confusing that it is best avoided until the cro becomes a tool for students to measure with?
And anyone have a good suggestion for Gary about how to show traveling sound waves in a medium, or a convincing story/sequence of demonastrations that make it seem strongly "more than likely'?
I think there is a mismatch between the Cartesian graph and what we are keen that other should understand . James - I'd blame the tools and not the wielder of the tools. Came across this today, which seems to 'fit' the lack of fit....
"Like all the best formalisms his diagrams avoided the need for thought. They had a structure that naturally implied where the next pieces had to fit. If you want to know what comes next.
as Feynman put it, ‘it’s like asking a centipede which leg comes after the other’."
Barrow: Cosmic imagery, p.504.
He was writing about Feynman diagrams, but here also I just would not start with the graphs - experiences with deciphering exam questions about snapshots fed into the sequence suggested in IRE01.
Two things that seem crucial are:
1.What IS a wave?
We need the exam board answer [transfer of matter without transfer of energy...]but perhaps something to help them get their heads around the concept. I have been moved by:
'some pattern [of 'wobbles'] that happens further away and/or later than it does here and now'. This certainly helped me with the idea of gravitational waves and it sort of caters for Mexican [crowd] Waves.
2. How can waves be represented?
(a) The diagram that lets us 'see' wavelength - A SNAPSHOT
Represented be a photograph of a wave [slinky or Rubens tube] at one instant
(b) The diagram that lets us 'see' period - A SHORT STORY or BIOGRAPHY of one particle or point.
Represented by some form of CRO or picoscope trace.
The big problem here, of course, is that the sinusiodal images look the same and students want to ascribe wavelength to the second diagram
(c) [And this probably doesn't apply at 11-16] An indication of the various frequencies/wavelengths that are present in a complex signal. Represented by a frequency spectrum [graphics equalizer?] or manifested by using a diffraction grating [especially for a line spectrum]
Only then can we go on to explain the behaviour of waves [no diffraction/interference in GCSE?] utility of waves and their fitness for purpose [ultrasound, X-rays, etc.].
On the whole snapshot line of discussion. I’m a fan of Randall Knights Five easy lessons and there is lots in the book I really love. When I first got the book, it was the first time I’d seen someone really try and pick apart a way of teaching – what a wave is doing and what the particles in a wave ate doing in a really structured way.
He suggests teaching ‘snapshot graphs’ showing displacement vs position at a point in time and ‘history graphs’ showing displacement vs time at a position in space. And then these together as a pair offer a way of representing the wave. It all seemed to make sense and I spent a while working through it all. I then ran a session for teachers and it just was a disaster, providing more confusion that help. One teacher commented “James you seem to have to tried to offer a solution to a problem that I didn’t think I had and still don’t and all you solution has done is confuse and upset me”. I can see how we need to separate the movement of the wave propagating ‘thing’ from the wave itself and this is key, but each time I’ve returned to Knight’s suggestion I’ve never really made much progress myself or with other teachers.
I cannot find an easy way to add images but on page 158/159 if you have the book you’ll see what he suggests, which I’m just not convinced by. Seems the effort:reward ratio doesn’t work in favour of the teacher or learner.
In the end I got a slinky and/or rope. Wobbled it and then tied a ribbon on to a point and then cued people in to look at that – seemed to do all I needed to separate the wave/oscillator.
The idea of "snapshots" is very powerful and I wonder if it's far more accessible now we have so many cheap cameras. We can do snapshots - where we have a set of physical descriptors that relate to a moment in time. But we can also do videos - where we have patterns in changes and relationships between physical descriptors.
This might help for CROs etc https://www.youtube.com/watch?v=IlgKpYJTwyM
The newsletter made me think about how we start with waves and some of the teaching limitations. One obvious one is teaching that "sound" is a wave. This is tricky because we are very good at hearing - if we were any better we'd hear thermal noise. So we can hear things that are very small effects. Thinking about the source - medium - detector model, being able to show that sound passes through the medium as a wave would be very nice. Except I can't think how we do it, especially given the comment I already made. So we could resort to showing that the source acts in a wavelike way, and likewise with the detector. That then leaves the medium acting in the same way as being quite probable, with a bit more evidence later in the form of Kundts tube. Does a Rubens Tube supply more evidence? I'd like to be convinced but I'm not. You can see sound here: https://www.youtube.com/watch?v=px3oVGXr4mo but it doesn't look that wave like and it's rather complicated to understand what you're looking at. It could be presented as evidence from authority, backed up by some socially constructed knowledge. But I think showing sounds travels as a wave in a medium is quite difficult and possibly a limiting concept?