Day 92: Circular Force Diagrams and Motion Pillars take 2

Advanced Physics:

Today we discussed the rotational kinematics assessment the kids took on Friday.  It continues to amaze me that even after a full semester with me, most of my students still reach for the equations….Here is  problem I gave them on the assessment

Screen Shot 2015-01-26 at 8.27.11 PM

It is REALLY easy to solve with an angular velocity-time graph, but tougher and longer with the equations… sigh.

We also looked at sample tangential velocity problem I asked the students work on over the weekend.

Screen Shot 2015-01-26 at 8.30.18 PM

That’s a picture of some wind turbines all my students have seen many, many times.   I asked them to determine the speed in miles/hour for the tip of the blade.  I provided them with the pdf of the design specs. The blade length is 134 ft and the operational rate is 14.4 rev/min….. the answer surprises most  138mi/hr.


After that we developed the concept of radial (or centripetal) acceleration.  I prefer radial because they are less likely to confuse it with centrifugal AND we hit a vertical circle we can discuss a tangential acceleration more easily.


General Physics:

We WB’ed the same set of motion pillars we used with the Advanced class.  I had 3 groups CYOP (create your own problem). One I used as an exit formative assessment, the other twoI will use as additional formative assessments.  We also just briefly started discussing how to draw force diagrams.  More on this tomorrow.


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