Re: [Phys-L] Sequence?

[jbellina <inquirybellina@comcast.net>]

The only thing about doing balanced forces after constant velocity that concerns me is that it perhaps may lead students to remain Aristotelean, thinking that forces create velocity rather than change in velocity.  What if you did changing velocity leading to the idea of force, then balanced forces.  
I have had  students do a number of real experiments and some simulations to see that when the velocity changes, the change in velocity can be associated with a force acting in the same direction as the chance in velocity.  This is all done with vector drawings and geometry, but no algebra.  The focus is on determining the direction of change in velocity not the magnitude.
Examples of the motions are starting and stopping, making a right angle turn, and going in a circle.
You could to the same thing in terms of momentum.  As I recall there is some evidence that doing momentum before force is useful, but others will be much more aware of that.

cheers,

joe

On Jun 21, 2012, at 10:27 PM, James Cibulka wrote:

> I've been thinking of following Kelly O'Shea's example and doing constant velocity, then balanced forces, then uniform acceleration followed by unbalanced forces with my 9th graders next year. 
> I was thinking it might help students to have another unit before uniform acceleration and it's curved graphs; as well as give some more meaning to what is happening when we squeeze projectile motion into the end of the uniform acceleration unit. 
> Any thoughts?  
>
> My current sequence:
> 1. Science skills ( now heavy on three act like tasks ala Dan Meyer)
> 2. Constant velocity
> 3. Uniform acceleration ( I currently do two days of projectile motion - I'd love to do more- it is interesting!)
> 4. Balanced forces
> 5. Unbalanced forces
> 6. Energy ( even though I believe it does not really exist) 
> 7. Mechanical waves and light ( end of the year whatever you get to is great unit!)
>
> Thanks!
>
> Jimc
> Kirkwood High School
>
> Btw, my unit assessments are now all goal less problems, graded on a rubric scale. 
> The students go as deep into the water as they can swim. Some swim very well, others not so much. All can do more in the water than when they got to swim class. I may not be highly anything, but I Model the best I can!
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Joseph J. Bellina, Jr. Ph.D.
Emeritus Professor of Physics
Co-Director
Northern Indiana Science, Mathematics, and Engineering Collaborative
574-276-8294
inquirybellina@comcast.net