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26 October 2017

Vertical motion simulator for changing g

Screenshot from vertical motion simulator
at computercow.net
One of my favorite early-season assignments asks how much higher or lower a ball will fly when g doubles.  Most students recognize, or guess, that doubling g leads to a halved maximum height.  To their chagrin, they also discover that doubling both the launch speed and the gravitational field does NOT lead to "canceled out" effects and the same maximum height.*

* ...because height goes as launch speed squared.

Even in the first weeks of class, my students expect experimental verification of mathematical predictions, especially counter-intuitive predictions.  But, I can't easily take my PASCO projectile launcher to a planet with gravitational field 2g.

And here, then, is a perfect place to insert an animated simulation.  I stay away from simulations because they're emphatically NOT real.  Physics is in the business of predicting how the natural world works, not how programmers make it seem to work.  Nevertheless, appropriate programmed simulations can be useful for giving students a feel for experiments that can't be quickly or easily set up in lab.  

Problem is: I've never found a free-fall simulation that allows me to change both g and the initial vertical speed with which an object is launched.  There are some wonderful dropped-ball simulators, and others that do a good job with projectiles.  But nothing purely vertical with a varying g and v0.  If you know of a free simulation that does what I want, please let me know in the comments.

(Barry Panas, the Official Humorist of the AP Physics Reading and master Manitoban physics teacher, is right now screaming at me the same way I scream at baseball commentators: The Interactive Physics platform will do exactly what I describe!  When I had IP installed on my old computers, I used to use it.  Barry taught me everything I know about using IP.  But, I don't have that program anymore.  I need something free and quick. Sorry, Barry.)

Good news - I have a student this year who's a programmer.  I explained what I was looking for; in a day, he had something basic but useful.  Take a look at this link. I don't exactly understand how the "pixel" button works, but it allows me to zoom in or out.

And so, after we did this problem, I projected this simulation in front of the class.  We doubled both g and v0, and wouldn't you know, the maximum height didn't remain the same.  Physics works.

Disclosure - the link is to my son Milo's site; he is the student who programmed the simulation.

08 October 2017

Should universities award credit for AP Physics 1? Yes, a thousand times yes.

Gary writes with a big-picture question about teaching college physics at the high school level:

A college physics course would be either 4 or more likely 5 credits.  A history or language course is often  a 3 credit college class.  Why do so many high schools  treat AP Physics the same as the other AP courses?  It is difficult to explain to students, parents, school boards etc that the AP Physics will require much more time and effort than students are used to... I know that many universities are concerned about giving AP Credit especially to science majors.

Firstly, a university "concerned" about giving credit at some level for AP Physics 1 either hasn't done their research, or is operating from a set of assumptions about what "credit" means which is as out of touch with the reality of my students' experience as the Republican party is out of touch with contemporary musical theater.

The answer to Gary's first question is sort of sad, and often damning to the credibility of high school science courses.  Teaching rigorous high school physics is incredibly challenging, because we have to know our content backwards and forwards, we have to develop unique pedagogy... but we also have to navigate the most difficult political environment this side of congress.  As far as I can tell from extensive anecdotal evidence and personal experience: 

1. Most high school administrations have no clue about the comparative difficulty of the AP courses.  They understand *that* lab exists, but they don't have a real clue why or how laboratory work should be done.  They see their students write baloney with big words in English class, and earn passing scores; but then the same technique earns a 1 on the AP physics exam because physics can't be finessed.

2. Sometimes when the administration does recognize that physics is a different animal, it's not politically possible to treat physics differently.  Let's say they give AP physics more class time, or more academic credit, or a smaller student-teacher ratio, or they give an AP physics teacher an extra planning period to set up laboratory work... there WILL be complaints about "fairness" from other AP teachers.  Not just administrators, but lots of other teachers think that school should be about reading a book, remembering what's in it, then BSing the way through a discussion and a paper.  Why should physics be any different?  After all, they hated physics.

But what I don't understand is why any of that should impact universities awarding credit for good scores on the AP Physics 1 exam.  

The AP Physics 1 (and AP Physics 2) exam is outstanding and challenging - much more challenging than a typical college physics exam.  A student who earns a 5 has not only shown extraordinary mastery of the requisite concepts and skills, but also the aptitude to handle any further physics topic you can throw at her or him.  A student who earns a 3 has not just thrown dung at the exam hoping some would stick; such a student has shown considerable though incomplete mastery of the topic.

As a rule, scores from the old AP Physics B exam have shifted down one number.  Students who get 4s on AP physics 1 would have gotten 5s on AP Physics B.  Most importantly, those who used to pass (i.e. earn at least a 3) on the old physics B exam do NOT pass the physics 1 exam.   Why?  Because a mathematically talented student without physics knowledge could, on a physics B exam,* plug random numbers into random equations and earn enough credit to pass.  Not so in AP physics 1.  There are no "pity points" of any sort.  If you pass, you understand.  

* and in most college courses - that's the university level's dirty secret

In my mind, universities should be actively seeking out students with passing AP Physics 1 scores in order to give them credit and woo them to their school.  They are well prepared: perhaps for a physics major eventually, definitely for any rigorous quantitative work at the university level.  And the ones with 4s and 5s - department chairs should be recruiting them as they would a quarterback with NFL potential.