AP® Physics: The Scaffolded Block Scenarios

Spring break is over and my seniors are struggling to find the purpose behind all of the work they are doing (or sort of doing) at school.  I'm not gonna lie: this is the hardest part of the year for me.  Not only is class time a struggle as I often feel like I'm dragging my kiddos through our last bits of content, but I'm also missing them already.  I can't believe how soon they are graduating!

To cope with my aftermentioned struggles, my thoughts always turn optimistically to next year.  What can I do better?  What did I love and want to do more?  What will I never do again?  I'm going to share something I want to do more of, but haven't quite figured out how.

In AP® Physics this year, I did something different when introducing Newton's Second Law and drawing free body diagrams (FBDs).  Typically, I would give the students a variety of scenarios to examine.  This time, I decided to take two critical scenarios for a block and examine every possible presentation.

Below, I have included what this investigation looked like in my forces packet.  Side note: I provide a packet at the start of each unit that students must bring to class.  The packet includes a section for notes, guided discussions, simple investigations, and problems.

Block on a Ramp

For this investigation, the students were presented with a block on a ramp.  By investigating each listed condition, the students:

1. were introduced to symbolic analysis of problems as they are used to numerical answers at this early point in the year.
2. realized that "at rest" and "at rest while on the verge of slipping" are different, even though the block is behaving the exact same way!
3. discovered at rest and moving at constant velocity are nearly the same (both balanced)!  The friction simply shifts from static to kinetic.
4. determined the component of gravity responsible causing the block's acceleration and that, like in free fall, the mass of the block doesn't contribute to acceleration.

Now, I am not saying any of this is ground-breaking.  In previous years, I covered these examples.  But this was the first time I did it all at once and so repeatedly and deliberately.  Now that I have done it, it seems so silly I didn't think of this before!  This year, more than any other, I have had fewer students simply assuming that any object at rest must be experiencing maximum static friction.  This was a pretty big win for me!  I'm confident other physics teachers out there can relate.

Stack of Blocks

For this investigation, the students were presented with a stack of blocks with the bottom block being pulled by a horizontal force.  This one was the most fun for me, especially when slipping began between the top and bottom block (condition 5)!  Through this investigation, my students:

1. reaffirmed the conditions for static and kinetic friction from the previous investigation.
2. found out they could look at a system of individual boxes or the boxes together!  This was really good for them to see and emphasized the importance of Newton's 3rd law.
3. discovered that, when the blocks had two different accelerations, they could not be combined into one system for second law (conditions 5 and 6)!
4. analyzed how the direction of friction changes with the direction of acceleration.

Again, I used to cover all of this in a series of problems over the course of the unit.  But doing this work all at once allowed the students to make the listed connections more strongly and more permanently than before.  Having them dig so deeply into these two examples made them incredibly aware of their own thinking as they constantly had to ask themselves what changed from the last time and does it matter.  I guess I'm saying I felt the increased "meta" going on.

Where do I want to go from here?

I want to shift the format of my packets to include much more of this deep-dive investigation.  Right now, my packets consist mostly of just really nice problems that touch upon all of the nuances I want my students to experience before we leave a unit.  I think they would benefit so much more from this deliberate, broken-down approach instead of tackling disparate problems right away.

I am adding this to my list of summer goals!