I’m sure everyone has a topic they teach where they teach it, the students look blank, you teach it differently, still blank, you then do it even differently, same response. Doubt, panic, fear! This happens to me every time I’ve taught Newton’s third law and then tried to bring back in balanced and unbalanced forces on one object.
In isolation, the two topics are fine. It’s at the point where they need to hold both concepts in their minds together that they realise they just don’t get it.
I don’t get it, miss
I can’t do physics
This is too hard
I don’t understand
The worst phrases for me to hear in my classroom. I must have taught these two topics somewhere between 5 and 10 times, to different groups. I know I’ll be teaching it at least to two different groups next year. It’s my teaching Achilles’ heel.
So why am I writing this and even admitting it? Well, firstly I’d like to reassure my employer that I get there in the end with my students. After a few lessons of working through it, exam questions, thinking, reflecting and (most importantly) giving them time to digest the new ideas and sort it out in their own minds, they understand the two topics. But I’d dearly like to be able to teach these topics in a way that doesn’t seem to require my students going through a confusing, doubt-their-own-ability phase. It doesn’t happen to anywhere near this degree with any other topic. I want to know if it’s just me? Is there a better way? is it just very difficult for year 10 to understand?
I’d also like to reassure other teachers that this happens (I hope?!) and we all (probably) have topics we find tricky to teach. Well, I do anyway.
So what’s the problem?
The two topics are very similar, but distinct. My students seem to have trouble distinguishing them. I’ve simplified it down to:
Interaction pairs: 2 objects, equal and opposite forces, forces are the same type and act on different objects.
Balanced forces: 1 object, forces can be different types, If they are not equal and opposite then you get acceleration.
The difficulty seems to be that the phrase ‘equal and opposite’ is thrown all over the place. I emphasise the fact that one situation involves looking at all the forces on 1 object, the other is about 2 objects interacting. We look at examples, do practical work. I’ve done it in different orders.
How can something be moving if the forces on it are equal and opposite?
Because the forces on that object are not all balanced. There is a resultant force on that particular object causing it to accelerate. The interaction pairs to the forces on that object are on other things. Look at the gravitational force, for example…
I can see why it’s quite confusing.
Is it just too difficult for year 10? I don’t think so. I see it’s challenging and makes them think. Perhaps it’s one of the first times they’ve had to actually understand a concept to be able to apply the rules to a particular problem? They try to apply the simple rules but find they need to figure out which of the two situations they are looking at and this is where a lot of them struggle. Last year I told my (very bright, top set) class that they would likely struggle with the next topic, but it’s ok, normal, and they will get there. They didn’t believe me, then everything I’ve described above happened.
Some students do get it straight away. Thank goodness.
I’ve talked to colleagues. They agree it’s tricky.
I’ve read lots of physics books in order to refine my explanations. I’m aiming for perfect clarity. I know I understand the concepts myself and this isn’t the source of the problem. (honest!)
I’ve read Making Sense of Secondary Science – Rosalind Driver et al and in here these issues are highlighted. I’ve followed the advice.
I’ve asked twitter for advice and shown my pupils the marvellous Veritasium video: Best film on Newton’s Third Law. Ever. (i.e. when despairing get someone else to explain it 😉 )
Is there a better way? Well, there must be. What is it? help me find a better way 🙂
NOTE: If you are unaware of the topics I’m referring to, you can find out more about them here using this link: forces. It is the BBC bitesize summary of the topic and you need to look at three pages.