tag:blogger.com,1999:blog-5088860151651047897.post8705592451483494050..comments2024-03-25T10:56:59.380-04:00Comments on Jacobs Physics: Graphs in laboratory -- a rubricGreg Jacobshttp://www.blogger.com/profile/03854009948036330746noreply@blogger.comBlogger3125tag:blogger.com,1999:blog-5088860151651047897.post-84672081089396236922011-06-28T15:49:29.479-04:002011-06-28T15:49:29.479-04:00The original question is from the 2010 AP Physics ...The original question is from the 2010 AP Physics B exam. I can't post it here because the College Board's lawyers would hunt me down. But the original question begins by deriving the formula relating displaced volume and mass... which gives a function with a nonzero y-intercept. That's why the best fit should not be forced through the origin here. <br /><br />As for log scales, you're right that scientists commonly use them. However, since I've never seen such a graph on either AP exam, I don't bother teaching their use except occasionally to my research course.<br /><br />GCJ<br />GCJGreg Jacobshttps://www.blogger.com/profile/03854009948036330746noreply@blogger.comtag:blogger.com,1999:blog-5088860151651047897.post-46634292594999275702011-06-28T15:39:58.161-04:002011-06-28T15:39:58.161-04:00There is something very wrong with Point 4.
If th...There is something very wrong with Point 4.<br /><br />If the model you are fitting is m = c v, with only one free variable c, then the line should be forced through 0. Fitting m = a v + b is incorrect, as that is not the model being fitted. Just because that is the best straight line for the data does not make it the correct model to fit!<br /><br />The underlying question determines what sort of curve to fit. If you are just trying to determine the density (and not questioning whether mass is directly proportional to volume), then only fits that go through 0 should be accepted.<br /><br />Also, it is actually extremely common as a scientist to use log scales or other non-linear scales rather than linear scales (though for this particular problem, linear scales are the most appropriate).Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-5088860151651047897.post-84746913522008665152011-06-17T15:55:49.311-04:002011-06-17T15:55:49.311-04:00Really good point, you can also set part of your l...Really good point, you can also set part of your lab rubric based off of experiment questions dealing with the following<br /><br />Draw a diagram of the experimental setup (2005 question 4, 2006 question 2)<br /><br />Showing explicitly how the equations are used to determine the experimental value (a lot of the experiment questions deal with this)Mr. Adam B. Kellamhttps://www.blogger.com/profile/07520550441007568844noreply@blogger.com