🚀 go-pugleaf

According to chem@uwpg02.uwinnipeg.ca:
>
> Hi. I know this group is for sharing resources but I need
> some help from human resources.  Being a novice high school
> Physics teacher, I've come across some problems with those
> pesky positive and negative signs with Coulomb's Law.
> Would I say to the students that two unlike charges experience
> an attractive force of -1 N (for example) or +1 N. Can the magnitude
> of ANYTHING have a negative sign in front of it? Thanks for any
> information. I appreciate it. Marsh Carroll
> internet:  chem@uwpg02.uwinnipeg.ca
>

My procedure: calculate the force using only magnitudes (absolute values
of the charges) and then use the picture of the layout to get the
direction of the force.  A force has magnitude and direction - it is a
vector.  Use the equation to get just the magnitude.  Use the picture to
get the direction.

I always found it hard to get the concept over that we are calculating
the force on one charge caused by another.  For example if we have this
setup:          |<----- 4m ---->|
                *               *
                q1              q2
                +2e-5 coul      -3e-5 coul

then the force on q1 caused by q2 is to the right.  The force on q2
caused by q1 is to the left.  The students seeing this for the first
time will usually draw the vectors representing these forces incorrectly
until I carefully coach them about it.

The force on q1 is given by:
                        |(9e9)(2e-5)(3e-5)|
                        -------------------=.3375 N to the right
                               (4*4)

-- Hope this helps.
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T. Boyd Moore - Physics & Math teacher, Caroline High School,
Milford, VA 22514.  KO4WK.  Galatians 2:20  e-mail:tbmoore@vdoe386.vak12ed.edu
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