Re: [Phys-L] sharing an activity re circular motion free-body diagrams

[Philip Keller <pkeller@holmdelschools.org>]

I agree -- in fact, that's exactly how we do it when we start.  But 
later, it becomes convenient to have quick,  one -letter names for the 
common forces.  Still, your system is likely to reduce one common 
student error: putting "normal" forces everywhere, even on objects in 
mid-air!  Less likely to put "Ftable" on a diagram for an object not 
actually in contact with a table!

On 12/9/2013 8:29 PM, Bruce Sherwood wrote:
> Nice exercises!
>
> One of the instructions is "Only include in your diagrams FORCES that you
> have learned about this year, such as tensions, normal forces, friction,
> and weight."
>
> Having chosen an inertial reference frame, you might consider asking that
> students identify the object in the surroundings that is responsible for
> the force. Naming objects is a general way to avoid noninertial forces
> and/or possible double counting. In other words, "string" instead of
> "tension"; "table" (perpendicular component) instead of "normal force";
> "table" (parallel component) instead of "friction"; "Earth" instead of
> "weight" or "gravity". You might also wish to ask students to identify the
> kind of interaction (electric or gravitational).
>
> Bruce
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