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Using The Rope Model of Electricity
In the next podcast we inevitably talk about the rope model. I tried it a few times in the past and hated it ?. It was only in making the podcast that I finally understood how to do it and how good it is. Not knowing how to do it is as much a function of my comfort with the donation model as it is my being alone in my school with no other physicist to talk to. But talking to Robin and Stuart about electricity really got me thinking.
When I did the rope model it didn’t work because I had quite a few kids involved in the demo. I found it really hard to make the rope run smoothly through their hands (not least because the rope had a huge knot in it!) and it was a very static sort of demo. There was no fluidity at all, no flow. I had visions of attaching pulleys to the walls of the room to make it work (I like big scale). I chatted to Stuart about this and he was able to tell me a way to do it that worked. It works so well, and is so easy to do. I was bowled over.
my recipe for an effective rope model demo:
- Have a rope that is in a 3-4m loop where the join is as smooth as possible. (Cutting and melting together a rope is ideal).
- Choose one student only.
- Hold the loop and pass the other end to the student. Tell them to grip it lightly (they don’t want rope burns) in one hand with the rope passing vertically down through their fist (this is the detail I never understood – one student, one hand).
- Explain that the rope is the electrons and the grip is the resistance.
- Pull the rope hand over hand through their (one, stationary) hand.
- Question: What do you feel in your hand?
- Answer you want: Warmer
- Tell them to add another hand, holding with the same light grip. The rope will get harder to pull, make this obvious, it will naturally run more slowly.
- Question: why is the rope moving more slowly?
- Answer you want: because there is more resistance.
- Question: how can I increase the current to make it move as fast as before?
- Answer you want: Pull harder.
- Explain that this means more energy being delivered by the cell to the rope, or greater pd.
- Pull harder, to make the rope move at the original speed again.
- Tell them to grip tighter with one hand, but not to tell you which hand that is.
- Question: what has happened to the rope speed?
- Answer you want: slower.
- Question: does the rope/the pd know which hand is gripping harder?
- Answer you want: no.
- Question: what is happening at the tighter hand?
- Answer you want: warmer.
- Explain how this is energy transfer
- Question: are the electrons in any way different before and after the hands?
- Answer you want: no.
- Remind them that electrons just go where they are pushed/pulled by the pd, they aren’t changed, they don’t make a choice, they just go where they go.
- Get another rope, get them to hold one loop in each hand, but you pull them together. You can model parallel with this but I wouldn’t go too far as the model does tend to break down a bit.
- You can show AC nicely too. Remove one loop then tell them to hold their fist horizontally, not vertically. Now grip the loop in both your hands and pull it backwards and forwards. The hand gets warm just the same.
Good luck with this. Maybe report back in the forum?
Somebody Out There Likes Us
Robin and I started with very limited ambitions, it wasn’t quite “more listeners than presenters” but not far off. We agreed to do episodes until the end of the academic year and then see where we stood. At that point we had not got much further than me telling Robin he and I should start a podcast and then months later him finding the statistic that about 50% of schools in the UK have one or zero physics teachers. We just wanted to try something, try to build a community and see what happened. I am a regular listener of The Cycling Podcast and modelled a lot of our approach on them.
As we started I had no idea about format, content, approach, social media, iTunes ratings, post production, how to talk to a microphone and had never considered a T-shirt or shop (or adding a forum) But I am top loaded with running web sites and general geekery, so I figured I would muddle through.
It was a revelation to me (physics teacher, but never an audiophile) to find that a microphone has preferred orientation. Listening back you can tell the episode where I worked out where to point my mouth when recording. I found a great T-shirt supplier when looking for somewhere to buy a jokey shirt for Robin. They actually make the shirts on demand and provide a WordPress plugin, so one thing led to another and now… a shop! Just a bit of fun of course, as Robin says in Episode 9, this is nothing about money… But if it helps build a community then that’s brilliant.
As I went to sleep on the night before episode 1 I was not convinced I wouldn’t grab my phone at 4am and cancel it. Now, as we approach the recording of episode 10 I feel more comfortable hearing my own voice. I’ve also been dragged kicking and screaming in to social media and I feel a community is growing. (We have had a few emails thanking us for doing it and the interaction on Twitter has been fun). It has also been hugely enjoyable talking to different people and learning from them: I recorded another PIM this week which will most likely be in Episode 11. Please do continue to send us ideas. We love hearing them all. You can use the form below.
Finally, to get some 5* ratings in iTunes is pretty stunning to be honest, so thank you very much, listener(s!).
9. Mentors, Motors and Merch
Robin hadn’t heard about the recent Falcon landing failure so Thomas filled him in. Cutting-edge space technology is still frontier science: we need your students to be the engineers of tomorrow! Regular listeners will know how much Matt Groening influences the podcast, and just in time fro Christmas, we have launched our first ‘merch’, setting up a shop on the web site. A shop where you can buy the T-Shirt? Yes, all your Christmas present problems are solved! Listen out for a secret (??) code that allows you to get your shirt at cost. This time next year we may be stocking TPTP box sets and underpants: our ambition knows no limits.
Care in the community…
Physics teachers can be empathetic too! Robin worries about how hard this time of year can be, and especially for young-in-service teachers and the terrific Jo Kent draws on her wealth of experience to give her advice. She highlights how an empathetic ear can make all the difference, and on a more practical note, how networking can help to build communities. She specifically mentions TalkPhysics and Thomas compares it to PTNC. (The IoP has a page where several other ways of networking are listed). Jo goes on to tell us about her Pint Pot Motors in a Practical In Memoriam. Below you can see the images she talks about below and she also sent us her PowerPoint and the video her father made.
It remains a privilege and a joy making this podcast for you. We love hearing from you and you are a very big part of the adventure; guide us, tell us what you want to hear about. It really is your podcast, so please get in touch: teachers of physics are our very favourite superheroes!
Jo’s Pictorial Instructions
A Working Motor
The Motor Jo’s Dad made:
Also Thomas made the motor and shared it on Twitter:
Join in!
Please share ideas or successes – or indeed questions by messaging us on BlueSky: https://bsky.app/profile/physicstp.bsky.social . You can also message us via our website contact form on every page of the web site at the.physicsteachingpodcast.com, or email using the address given in the podcast (if we remember). We are moving away from X but can be found there as @physicstp.
Music
- Season 7: Physics Is Our Business by Miracles of Modern Science.
- Seasons 5 and 6: Crescents by Ketsa.
- Seasons 3 and 4: Disco Sheik by Podington Bear.
- Seasons 1 and 2: One legged equilibrist polka by Circus Homunculus.
- Occasionally we also use Cantina Rag by Jackson F. Smith.
The music is used under the Attribution-NonCommercial 3.0 International License
8. Venn Hats, Meows and a Mysterious Tube
Mr Benjie As David Bowie once mused “Is there seismic activity on Mars?” ( I think that’s what he said…), and who are we to argue? So we kicked off discussing NASA Mars Insight Lander and then Robin confessed to group about his tendency to get on a self-righteous soapbox (see episode 7!). Luckily this week’s chat was the perfect antidote to stress as he chatted to Carole Kenrick: primary teacher, secondary teacher, artist and PhD student, she wears many metaphorical hats … and has a podcasting cat called Mr Benjie.
Carole tells us about two of the practicals she likes the most: decay-dice and mystery tubes. Decay dice take the simplicity of rolling one die, developing it in to a beautiful mathematical model. She uses mystery tubes from the Berkley Understanding Science web site and they kindly provide instructions to make them. Thomas couldn’t resist making a mystery tube of his own and “Thomas from the future” appears to tell how he got on.
Thomas’ early prototype Carole also introduces us to “Physics Fairy” (no, really, check it out!) and explained how it came into non-existence from working with Force Goggles from the Supporting Physics Teaching web site.
New Competition – Closes 13th December
Help us with our planned “Electricity” episode by giving us your top tips… and pitfalls. Either tweet us with the hash tag #physicstpelectricity or comment in the thread on our Facebook page. Thomas and Robin will choose a winner on the 13th of December and will send you a signed copy of Ben Rogers’ wonderful book The Big Ideas in Physics and How to Teach Them.
It remains an enthralling and educational adventure making this podcast for you. We love hearing from you and you are a very big part of the adventure; guide us, tell us what you want to hear about. It really is your podcast, so please get in touch: teachers of physics are our very favourite superheroes!
Join in!
Please share ideas or successes – or indeed questions by messaging us on BlueSky: https://bsky.app/profile/physicstp.bsky.social . You can also message us via our website contact form on every page of the web site at the.physicsteachingpodcast.com, or email using the address given in the podcast (if we remember). We are moving away from X but can be found there as @physicstp.
Music
- Season 7: Physics Is Our Business by Miracles of Modern Science.
- Seasons 5 and 6: Crescents by Ketsa.
- Seasons 3 and 4: Disco Sheik by Podington Bear.
- Seasons 1 and 2: One legged equilibrist polka by Circus Homunculus.
- Occasionally we also use Cantina Rag by Jackson F. Smith.
The music is used under the Attribution-NonCommercial 3.0 International License
Refutation Text for the Jelly Chair
I said in Episode 6 I would share what I came up with for the Jelly Chair lesson and refutation texts. I did put some thought in to this but think that there is room for improvement. I ended up writing a few sentences for the kids to do:
- The ancient Greeks thought that arrows were pushed through the air by the god Apollo. We know this is wrong because…
- Many people think that objects will slow down and come to rest if no resultant force acts upon them but really…
- A typical GCSE level understanding of balanced forces allows a person to sit on a chair made of jelly. This is false because…
- Galileo showed that two balls of different weights accelerate at the same rate when dropped.. Before this people thought heavier objects fell faster but this is wrong because…
- Some people think the International Space Station has no forces acting upon it because it is in Space, the evidence that they are wrong is…
- When a helicopter is hovering it is very common for people to think that the weight of the helicopter has an equal and opposite force that is the down-force from the rotors. This is wrong because…
I was particularly happy with the last one (though I have no idea if that is an actual misconception or not), and even happier when one of the students said something like:
The down-force is equal to the weight!
They had truly understood the situation, and was able to explain to their partner that the weight and down-force must be equal in magnitude and in the same direction as weight if the helicopter is hovering (not equal and opposite).
As I roamed the class and spoke to the students I was pretty confident the refutation sentences were having impact. The challenge is to use them again and again and embed them in my practice.
The podcast strikes again. Thank you Ben Rogers!
Kicking a Rock on the Moon
In Episode 6 I mentioned a thought experiment with a concrete-filled rugby ball. I have used this model for years and knew it came from a text book long ago and I have since been searching for it. I was convinced it came from Peter Warren, the head of department where I did my teacher training and author of one of the books that was used to teach me back in the early 80s. It turns out that Pete is still teaching, but did not draw the cartoon.
It actually came from Physics for You by Keith Johnson, and it is still available, new from Amazon in the 5th addition. I actually own a Johnson (it has sat on a shelf in my office untouched for years) and did not think to look in it until I had sourced a couple of Warrens from amazon. The character kicking the rock (in this case) is Professor Messer. I assume Johnson drew them all himself, as did Pete in all the cartoons in his books. I excitedly looked up @ProfessorMesser on twitter to see if he had an online presence but it turns out to be a real person.
One of the Warren books I sourced is a gold mine. It is the advanced physics laboratory book and this would be a super resource for anyone new to A level teaching. I got it for 20p just a week ago but a quick check on amazon shows it is now £28+! It contains many practicals that I consider routine but has given me some new ideas too. For example, my school does not have a position sensor/force sensor etc. so I have not been able to datalog damping. This book has a beautifully simple way of doing it: attach a magnet to a hanger boinging on a spring, bounce it up and down inside a coil and measure the current in the coil.
7. Ben, Big Ideas and beginnings
Thomas and Robin talk about the podcast’s roots and where it all started, to help all teachers of physics to feel a sense of professional community. You can help by sharing it with your friends, and if you do that you have a chance to win a podcast T-Shirt! The competition lasts until 30th November 2018 and the winner will be announced in the Episode 8.
We were joined by author and all-round lovely man Ben Rogers, whose books The Big Ideas in Physics and How to Teach Them is taking the physics teaching community by storm. Ben tells us about cognitive science (links below); why he is not opposed to practical work, and how he came up with all the history and characters in the book.
Thomas enthuses about the versorium needle (everyone should make one).
Robin was on his soapbox again (it happens, just ignore him) encouraging teachers to avoid the temptation to treat new ideas as how they should be teaching, rather to use the ideas to enhance the good practice you’ve built up.
Versorium (needle)
Ben’s References for Cognitive Science
- John Hattie – Visible Learning
- Twitter Daniel Willingham has a web site and is on twitter as @DTWillingham, Dylan William (@dylanwiliam)
- Niki Kaiser (@chemdrk) is a chemistry teacher and gatherer of people – she’s very well informed in CogSci and you can read her blog.
- Learning scientists (http://www.learningscientists.org/) have podcasts and downloadable resources.
…and finally
Don’t forget to enter our first competition. Win a beautiful podcast T-shirt (in the colour of your choice) by interacting! To win, tell us why you like listening. There are many ways to do this:
- You could tweet us (@physicstp).
- You could use the contact form below.
- You could share our Facebook page.
- You could follow us on the new Instagram page (@physics_teaching_podcast)
- You could leave a voice memo to +44 7898 814716 on WhatsApp or Telegram (don’t forget to say your name)
Thomas and Robin will pick a winner and announce it in Episode 8.
It remains an engrossing and uplifting adventure making this podcast for you. You’ve already taken it in directions we weren’t expecting; it really is your podcast, so please get in touch: teachers of physics are our very favourite breed of hero!
Join in!
Please share ideas or successes – or indeed questions by messaging us on BlueSky: https://bsky.app/profile/physicstp.bsky.social . You can also message us via our website contact form on every page of the web site at the.physicsteachingpodcast.com, or email using the address given in the podcast (if we remember). We are moving away from X but can be found there as @physicstp.
Music
- Season 7: Physics Is Our Business by Miracles of Modern Science.
- Seasons 5 and 6: Crescents by Ketsa.
- Seasons 3 and 4: Disco Sheik by Podington Bear.
- Seasons 1 and 2: One legged equilibrist polka by Circus Homunculus.
- Occasionally we also use Cantina Rag by Jackson F. Smith.
The music is used under the Attribution-NonCommercial 3.0 International License
Entries! and Momentum Round-Up
We put out the competition not really knowing quite what to expect. Four entries before 8:15am was an exciting start to the day though as I write at 4:30pm it is still four, which has brought me down to Earth somewhat!
Momentum Day
Today was “Momentum” day. After talking with Ben Rogers about cognitive Science (that is in the next episode) I changed the demo away from play (the students making the rockets) and in to a demo so they could concentrate on the key idea of impulse (Ft) being more for the longer rocket, and hence v being higher. I made four rockets myself before the lesson. Showing them the rockets was actually a good way to mention to them that a vernier can be used for internal diameters too. I tried to make all the tubes the same diameter, but it was pretty hard and I think this led to the inevitable inconsistencies in the heights.
There was much uncertainty! The pump was definitely pretty rough at the low pressures I needed to keep the long one below the ceiling, the diameters of the rockets and the release of pressure through the valve all affected each launch. The results were not quantitative at all (my main aim) but it was clear that the longer went higher (on average). I think if I made better rockets on fixed tubes it would be more successful, it is certainly worth pursuing. More massive ones would allow more pressure too.
But as a learning demo it was very good. The idea of the force being constant as the rocket launches and the longer rocket being in contact for a greater time made it easy to imagine impulse and relate it to velocity. At least I thought so. Time will tell.
An Unexpected Misconception
What surprised me was that one person thought that the smallest rocket would go the highest. I’d said that all were made from one sheet of A4 so all were the same mass, but suspect that they were thinking “small is light”.
6. What happens when your jelly won’t hold your weight? Is it time to lose some mass?
Jelly chair aftermath Thomas and Robin got together in the same room for a chat this week. Don’t worry, as a good physicist and a good engineer they avoided eye contact*. The big news last week was the redefinition of the kilogram which was originally based on the mass of Napoleon’s leg**, but latterly on a lump of metal held in what looked suspiciously like a cake container. So we discussed misconceptions about mass and weight and about one of Thomas’ favourite experiments: the jelly chair.
*Well, that’s an unhelpful stereotype! In fact we were highly empathetic and talked about our feelings extensively.
**completely made up
Competition!
Now we have listeners, AND an Instagram page (@physics_teaching_podcast) we thought we would encourage you to share the podcast by having our first competition. Win a beautiful podcast T-shirt (in the colour of your choice) by interacting! To win, tell us why you like listening. There are many ways to do this:
- You could tweet us (@physicstp).
- You could use the contact form below.
- You could share our Facebook page.
- You could follow us on the new Instagram page (@physics_teaching_podcast)
- You could leave a voice memo to +44 7898 814716 on WhatsApp or Telegram (don’t forget to say your name)
Thomas and Robin will pick a winner in a couple of weeks.
It remains an enthralling and inspiring adventure making this podcast for you. You’ve already taken it in directions we weren’t expecting; it really is your podcast, so please get in touch: teachers of physics are our very favourite breed of hero!
Join in!
Please share ideas or successes – or indeed questions by messaging us on BlueSky: https://bsky.app/profile/physicstp.bsky.social . You can also message us via our website contact form on every page of the web site at the.physicsteachingpodcast.com, or email using the address given in the podcast (if we remember). We are moving away from X but can be found there as @physicstp.
Music
- Season 7: Physics Is Our Business by Miracles of Modern Science.
- Seasons 5 and 6: Crescents by Ketsa.
- Seasons 3 and 4: Disco Sheik by Podington Bear.
- Seasons 1 and 2: One legged equilibrist polka by Circus Homunculus.
- Occasionally we also use Cantina Rag by Jackson F. Smith.
The music is used under the Attribution-NonCommercial 3.0 International License
Interact and Win a T-Shirt!
Now we have listeners, and an Instagram page (@physics_teaching_podcast) we thought we would encourage you to share the podcast by having our first competition. Join us at the bottom of an exponential by winning a beautiful podcast T-shirt (in the colour of your choice) by interacting! To win, tell us why you like listening. There are many ways to do this:
- You could tweet us (@physicstp).
- You could use the contact form below.
- You could share our Facebook page.
- You could follow us on the new Instagram page (@physics_teaching_podcast)
- You could leave a voice memo to +44 7898 814716 on WhatsApp or Telegram (don’t forget to say your name)
Thomas and Robin will pick a winner in a couple of weeks.