So you do understand Physics – You just thought you didn’t

Could we try a new approach to learning physics?

What if we start with the premise that our students intuitively understand lots already. Having done a project with Arsenal on the physics of football with the Institute of Physics, I was struck that the players were applied physicists, they knew the laws of physics so well they could make the ball do pretty much everything they wanted. What they couldn’t do was communicate how they did it in scientific language. I could get the ball to pretty much do nothing that I wanted , but I could explain what they were doing (to a point)

If we used this paradigm that for many topics we can start with this understanding then add the knowledge and language to allow them to communicate it. We might then transform some people’s perception of physics from mysterious and difficult into something that makes sense to them.

What might this look like in a lesson? `these are early ideas so please feel free to comment and improve and develop.

Centre of Mass Lesson

I didnt have access to technology so instead of using socrative I used post-it notes. Asking the students to write what they knew about centre of mass and putting it on a window that displayed their confidence. High , Medium or Low confidence. I was interested in those with high competence, but low confidence, these are often girls, but far more important are the low competence and high confidence students, usually boys, these I am going to have to destroy their misconceptions before I can teach them.

It appeared most had no idea what centre of mass meant and confidence in what they had written was low.

I started with the matchbox trick . See the video below and immediately beat five of them. I could make my matchbox stand up and theirs all tipped over.  I also did a ridiculous suck and wobbled my finger slowly which was enough to fox them.

Can you work out what I did?


I then gave them an empty matchbox per table and they had to figure out my winning strategy.

Next was the juice carton dilemma. You have a full, empty and half full carton. What order will they fall over in if pushed until they topple?


“Which would fall over last? (at the greatest angle) Left hand up for full, right hand for empty and both for half.” Few got the right answer

“Find a person who disagrees with you and try and convince them you are right. You have two minutes before I ask again.” A slight increase in numbers with the right answer

“Lets see if you are right…(Lines up cartons) … Actually lets leave it “ Complaints from class, “we want to see it now!”

Its the Zeigarnik Effect in action – Keep them thinking for longer

“I’m now going to beat you in another competition…(Draws circle on the classroom floor) …”A simple competition to try and push each other out of the circle. Have we a volunteer?”  Biggest lad steps forward  “Now I am going to step outside and give you a minute to train your champion. How should he stand? What strategy should he use?”

Goes out of room.

Comes back after a minute and stand eyeball to eyeball with Mohammed – Mohammed couldn’t look me in the eye!

“So how have you told your champion to stand?”  Mohammed crouches low, with a wide stance.

“Hang on a minute, you told me you didn’t know anything about centre of mass, but you do understand it as well as stability.”

This is the different paradigm, the knowledge is shared with them at the point where they need it. Most people intuitively get physics, but are poor at communicating their understanding in the standard way that scientists need

Then we have a discussion about centre of mass, what it is, how to find it (balance point) and stability , wide base etc At this point it makes sense to them. They intuitively know it. I am just modelling a scientific way of describing what they already know. To give them the language they need in order to communicate their understanding effectively

I then tell them I’m not happy with their choice of champion and choose a small girl (have checked she is ok with this first) Outrage from class

“Whats your problem with this? “ Lots of discussion about size – size or mass? “So you understand how forces work too. For any given Force that I can exert there will be a bigger change in the motion of Anna than there will Mohammed” – Leads into a discussion of forces and Newton’s second law.

Back to the cartons

“Which one now? Hands up – Now persuade others you are right “ – now around 90%

“So let’s see….. actually lets leave it for next time.” One girl shouted out

“What! you are going to leave us in suspense? “

“I certainly am!”

“You are the most annoying teacher alive!”

“Thank you, I’ll take that as a compliment!!”

Other fun stuff to do with Centre of Mass

But who has a lower centre of mass . Men or women? and how can you find out without any equipment?

How can you balance on a single point on the side of a glass two forks and a toothpick ?

How is it possible to jump over a bar, but never have your centre of mass go over it? (fosbury flop)

3 thoughts on “So you do understand Physics – You just thought you didn’t

  1. Hey Neil, as a novice Physics teacher (3yrs) my fundamental approach to many aspects of what we teach is that they already know and understand what we’re going to talk about. I try to explain that it’s a phenomenon they see on a regular basis – I’ll just be teaching the language to express it scientifically. The same applies to moments – a brief demo and they realise they instinctively ‘know’. Doesn’t work for everything but as an attitude to Physics I find it reassuring for them.

    1. Hi Marvin, for many students it boosts their confidence, which in physics can be very fragile. Will be posting other lessons up in future – stay in touch and share your ideas please!

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