We just did an N2 lab in which the acceleration of a cart was measured
for various applied forces. Friction was not mentioned. The students get
nice linear data which they graph and model in the form y = mx + b. (F
= mass x acceleration + friction). The y-intercept is the cart's
friction. In talking about the straight line graph of a vs F, I used the
term "directly proportional" to describe the relationship between F and
a. One of my students called me on this pointing out that in math class
they had just learned that it was only "direct variation" if 'b' was
zero. He's right. Of course Fnet (in this case F minus 'b') and 'a' ARE
directly proportional. But what about y and x in y = mx + b?
My question is, what do I correctly call the relationship between F and
'a' as graphed. Is just "linear" the right term to use? Is there another
name I should use?
Dave
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David A. Simmons
St. John's Jesuit High School
Toledo OH
<dsimmon@uoft02.utoledo.edu>