Re: [Phys-l] What are your answers for this teacher?

["Anthony Lapinski" <Anthony_Lapinski@pds.org>]

I've heard of this method. I've never used this method. None of my
students have either. But if it works, I see no problems with it. However,
many problems in physics require multiple steps with unit checks. Here's
one from electricity for my regular physics class (juniors and seniors).

You connect a bulb to a 6-V battery, which delivers 81 kJ to the bulb in
five hours. What is the resistance of the bulb?

Not a simple "plug and chug" type of problem. You have to know your
physics to get the correct answer.


Forum for Physics Educators <phys-l@carnot.physics.buffalo.edu> writes:
> Today's first PTSOS post:
>
> My 9th grade physics students were taught a method for solving speed
> problems in middle school that does not require algebra. The variables
> are separated in a diagram of a triangle (or a circle). When you cover up
> the variable you are solving for, the diagram shows you the recipe on how
> to solve the problem. If you're not familiar with what I'm talking about,
> here's a link to an example using Ohm's Law:
> http://www.electronics-tutorials.ws/dccircuits/dcp_2.html
>
> I have avoided use of this device for a variety of reasons. First of all,
> it has zero meaning. I feel that it is important to reinforce my
> students' algebra skills, which this method completely skips. I also
> prefer Hewitt's method on using equations as "guides to thinking" which
> these triangles/circles avoid. Finally, I have found in the past that
> various memory devices in math (e.g. FOIL, cross multiplication, etc.)
> have limited function and students tend to use them incorrectly much of
> the time.
>
> However, I am wondering if I should reconsider my stubborn position. I
> have had many students approach me this year showing me the triangle and
> claiming "here's an easier way to solve the problems!" In addition, at
> the NSTA conference I was introduced to a text entitled "Active Physics"
> by Arthur Eisenkraft which uses the circle for every equation given in
> the book.
>
> Again, these are 9th graders I am teaching, so maybe I should not be such
> a stickler on going through all the algebra. This device is primarily
> used for "plug and chug" problems anyway, which have little meaning
> themselves.
>
> Do any of you use this method with your students? Have you found it
> useful? Do you have any tips to make it more meaningful and universal? Do
> you see it as a hindrance?
>
> Thanks in advance for your collective knowledge and wisdom!
>
> bc thinks the picture is not a model.
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