The context doesn’t change the laws of physics

No, I didn’t stay up to watch the New Zealand v Slovakia game last night. Based on the grand sample size of one match each, NZ is as good as England. Not sure who that compliments / insults, though for you UK readers (I know there are some), the public reaction here to a 1-1 draw is somewhat more positive than it will have been back in Blighty on Saturday night. Total delerium would be one way of putting it – anyone would think that NZ has won the whole tournament, rather than just a point.

Anyway, that’s a sidetrack. Today I visited one of the local Hamilton schools following a request from a teacher to help his top students do some preparation for the scholarship physics exam. Before I went, I did a bit of preparation by looking at the previous year’s exam paper and the examiners’ comments on it. As usual, there are a few themes that I have read before.

The first one is ‘read the question’. I’ve mentioned this a lot before, but really, for those of you sitting exams (any kind of exam) it is the most important thing you can do. What I mean is read the question properly, and answer the question that has actually been asked, not the question that you would like to have been asked, or the one that you think should be asked.

Another one is that students seemed to get into a flap about the laws of physics when confronted with a context they hadn’t seen before. No, the examiners didn’t use the phrase ‘in a flap’, that’s my colloquial paraphrasing, meaning that students, when seeing something that looked new, forgot their physics principles. 

An example – conservation of momentum applies wherever you are (so long as their are no external forces). It doesn’t matter if your collision is between equal mass frictionless pucks on an air table (a familiar context to physicists) or two cars on a road resulting in debris strewn over tens of metres, conservation of momentum is going to be appropriate. The situation may be unfamiliar, but the laws of physics don’t change, and still apply. The trick is to see how to apply them to the particular situation you have. It’s not always easy, and takes a bit of practice.

So here’s an example question , for would-be scholarship examinees. Estimate the force that Winston Reid applied to the ball in his stunning header last night. In the spirit of Dan Meyer, I give no details about the velocity of Shane Smeltz’s cross, the mass of the new football, the distance of Reid from the goal, etc.  That’s for you to estimate. But I remind you that, as always,  normal laws of physics apply. 

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