20 April 2020

Understanding experimental physics is critical - even in 2020 with no lab design question!

I'm often asked, "Give me a straight answer - will experiments be tested on the 2020 online AP Physics 1 exams?" 


The straight answer has two parts: (1) While in a normal year one question is devoted predominantly to experimental design, such a question will not be included on the special 2020 exam.  (2) All physics refers to real experiments. You must therefore understand the physical -not just mathematical - context of every question!



Here's how I explained this on the April 8 AP prep show:


I teach at Woodberry Forest School, a country club for dogs in central Virginia.  Or, at least that’s what our empty campus feels like in the evenings, as the faculty take their nightly dog walks en masse – a mass of dogs. Usually, the dogs are far outnumbered by 400 boys living in the dorms.  And I long for those usual days to return.

We know what kinds of problems you’ll see on the AP Physics 1 exam on May 14.  The second problem will have a 15 minute time limit, and will ask you in large part to respond with a “clear, coherent, paragraph length response.” Think of that the same way you’d think of a “justify your answer” question – just use about five sentences instead of about two.

The first problem will have a 25 minute time limit, and will be a “qualitative-quantitative translation” question. Think of that as just a normal physics problem, but one unlikely to use numbers. You’ll be asked to relate algebraic expressions to physical behavior. That is, here’s some math, here’s an experiment, explain what features of the math explain the behavior of the experiment.

Notice I said “experiment.”  Wait, I thought the “experimental design” question wasn’t on the 2020 exam!  It’s not.  But every physics problem that can possibly be posed must be based on a real experiment – otherwise it’d be an abstract mathematics problem, not a physics problem.

See, that’s what physics is, at its very heart – predicting how the natural world behaves, using mathematics. 

So don’t be surprised when that first question asks something like “What would happen if we increase the cart’s mass?  Explain without using equations.”  You will have to use your experience, along with a conceptual understanding of physics principles, to imagine and describe how an experiment would behave. 

How do you prepare for this kind of question?  By doing the kinds of problems that you've been doing all year - including experimental design questions. Not just “what is the numerical value of the cart’s acceleration” but also “how would that acceleration change and why,” “explain in words how you determined the cart’s acceleration”, and even “what does an acceleration of 4 m/s2 mean about the motion of the cart?”  In other words, just do physics.  And that includes an understanding of how mathematics describes... experiments.  

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