Sunday, October 12, 2008

Letting go of Newtonian mechanics

I'm finishing my unit on uniform circular motion and gravity. We'll test on that this week and move on to momentum.

In the rearview? Preliminaries, motion and inertia, force and interaction. That is, kinematics and Newton's laws. By week's end, I'll be done with the first of California's 9-12 Physics Standard Sets (Motion and Forces) and started on the second (Conservation of Energy and Momentum).

I say this as someone who will not make it through all California's Physics Standards by the time the Physics CST strikes in April.

And I say it as someone who imagines there are many California high school physics teachers out there not as far into the curriculum in mid-October. I know we all love our mechanics topics and could spend the entire year deeply immersed in them, but that typically requires sacrificing rainbows and blue skies.

It's worth mentioning The Hewitt Doctrine: "Don't Let Kinematics Become a Black Hole of Physics Instruction." Conceptual Physics author, Paul Hewitt worries that we'll spend half the year working with ticker-tape timers and increasingly trickier graphical and algebraic kinematics puzzles, only to run out of time before giving students even the most rudimentary exposure to electricity, magnetism, optics, or many other fascinating topics in introductory physics.

Conscientious physics teachers fear that without a thorough understanding of motion and forces, students will not be able to grasp subsequent topics in physics. This turns out to not be the case. Very little of the sky falls if you move on from mechanics before it's fully fermented.

The deep understanding of kinematics and Newton's laws that most physics teachers obtained on their way out of college should not be expected of high school students in their first exposure to the topics. They don't all really need it.

I recommend letting it go and moving on.

If anything, students need more time with electricity and magnetism. These topics are very abstract, so lab work and slow development of concepts is called for. Of course, the year is finite (180ish days). If you're going to have a chance at E&M, you're going to have to get out of mechanics earlier.

Just a thought. Double your money back if the advice doesn't work for you.


dt said...

Dean, I quite agree with your letting go theme...having finished circular motion and working to let go of Gravitational Forces...

I usually go to E & M next with Momentum etc in December.

Any comments to guide me about the advantage of Momentum before Electricity and Magnetism?

David Tillay
Vallejo High School

Brian said...

Hi there! Just came across your blog and have been enjoying it.

It's interesting that you posted this as it is something that I am struggling with this year as I adopt a modeling approach to teaching physics. Modeling takes such a long time to accomplish that I am really worried about dropping a significant portion of the material.