Day 68: More Force Diagrams and Graphically solving ca problems

Advanced Physics:

As I mentioned yesterday, we finished the force diagram practice sheet.  Here is a picture of the set-up I used to check how the tension forces change withe length of the string and the angle they are at.


It is a bit hard to see, but the tension for on the right is larger than the one on the left because of the angle each makes, even though the string is shorter… this was a bit o a disconnect for some students.  I started this sequence with the same two strings at the same angle, so the tension forces were the same.

Here is another type of force diagram they did:

Screen Shot 2014-12-08 at 8.32.11 PM

I like this one because it is open to some interpretation (cv or ca) and it requires the students pay attention to third law pairs.


General Physics:

We finished WB’ing the graphical approaches to the constant acceleration problems.  The last one we worked on in small groups was a goal-less problem about a cheetah running at cv, the ca, then more cv.  The problem they solved in small groups once the had created the v-t graph was to find an instantaneous velocity during a period of acceleration.  It could easily be solved by just looking at the graph, although some students found the acceleration, then used it as the slope to determine the velocity.  One young lady asked what the area trapped by an acceleration graph represented!!  AWESOME.  We worked through what it represented as a class and then we decided that we could also solve the instantaneous velocity problem using this approach because the initial velocity was known.  Did I mention AWESOME.


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