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Oh the joys of grading

  1. Oct 31, 2006 #1
    I have the good fortune to be a TA this year. I have never taught before, and this has turned out to be as much a learning experience (probably more so) for me as for the students.

    I think I have a nobel prize winner on my hands, though... In his/her discussion of the ballistic pendulum experiment, one student informed me s/he measured negative kinetic energy. I had to laugh... I know I know.. it's rotten to laugh.... but WOW.

    It rather frightens me that some of these students are going to go on to be engineers... no wonder rockets crash into the ocean... most of them can't convert units properly.

    Venting over.
  2. jcsd
  3. Oct 31, 2006 #2


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    Obviously I don't know his/her actual thoughts... but keep in mind that it's intellectually dishonest to fudge the results to conform to what is supposed to be true.

    I know on one occasion I had to report, in the conclusion to a chemistry lab, that something had negative mass. Of course, I know that's almost certainly wrong, so I probably messed up a measurement somewhere along the way. But... when I computed the mass, it was negative, and it would have been wrong to say otherwise.
  4. Oct 31, 2006 #3
    A friend of mine TA'd for an introductory astronomy class. He said in one of the lab reports the kid was complaining that there should be some sort of machine invented to deal with numbers more quickly than he can do them out on paper......
  5. Oct 31, 2006 #4
    heh, I did neglect to mention that in his data table the values were all positive.

    He also stated that his initial momentum was greater than his final, but upon looking at his numbers the opposite is in fact true, by almost a whole order of magnitude.
  6. Oct 31, 2006 #5
    Last year I set a question where they had to work out the length of a bunjee cord. It was a little disturbing that a large proportion of the class thought that the heavier guy warranted the longer cord...
  7. Oct 31, 2006 #6
    Damn I can't even make up some sort of misguided logical progression to find a reason why they would answer that! >.<
  8. Oct 31, 2006 #7


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    Incentive to go on a weight loss plan? :rofl:

    ptabor, don't give up hope. Plenty of students just rush through their assignments late at night the day before it's due, and as such, spend very little time actually thinking about it as they're just trying to get words or numbers on paper to turn in.

    Are you just grading, or do you actually help teach the class? If you're teaching, then you have an opportunity to help engage their brains back in gear here rather than letting them keep sliding along without thinking about what they put on paper. Or, to correct misunderstandings or lack of understandings of the concepts.

    Pick a few examples like that one, where the mistake shows they were not paying attention to basic concepts, not just a multiplication error somewhere, and as you hand back the lab reports, ask if there's a such thing as negative kinetic energy. Remind them that the best way to check for errors is to ask themselves if the answer makes sense. If you get a negative answer for something that can't be negative, you better check where you lost a sign somewhere. Hopefully this will catch the attention of at least some of the students and spare them from such errors in the future. Others will still treat classes as opportunities to nap between parties, but you can hope that the message will sink in eventually for them too.

    In order to keep from getting too frustrated, remember that they are taking classes because they need to learn, not because they know everything already (even if some have the attitude that they do). It's better to make mistakes and learn from them in the class than once they get out into a job where there's no tolerance for such mistakes.
  9. Oct 31, 2006 #8


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    I hear you. I had similar experiences when I was teaching graduate students. :surprised

    I once graded a paper that had negative number of neutrons (negative flux, with flux being a positive scalar). Now bear in mind the flux distribution was being described spatially by a trigonometric function (sine/cosine), and trig functions can be negative. However, the fact it didn't occur to the student that a negative number of something physical didn't make physical sense was very worrisome, and the fact the student was a graduate student. So, not singling out anyone, I had a discussion with the class.

    Students are expected to make mistakes, but hopefully by the time they graduate, they will be more thoughtful and careful.

    How many of us have been 100% correct, all the time, i.e. how many of us are so absolutely perfect that we never make a mistake?
  10. Oct 31, 2006 #9


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    PF Members are perfect, so who are you asking? :smile:
  11. Oct 31, 2006 #10


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    Dearly Missed

    I managed at one oral exam to forget to include the work of external forces in an energy balance consideration.
    When the professor harrumphed ominously and came with a well-deserved acid shot at me, I got back on track again and got a good grade.
  12. Oct 31, 2006 #11


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    In my oral qualifier for PhD, I conceded that I did not remember the specifics for calculating the dynamic quality of a two phase flow, but I did know where to find it. :biggrin: Thermodynamics of fluids was not my specialty, although I could have spent more time studying it.
  13. Oct 31, 2006 #12
    In one of the papers I marked, the student listed all the primes to brute force a question. Good thing there are only like 15 primes. :wink:
  14. Oct 31, 2006 #13


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    HAHA! I would have laughed.
  15. Nov 1, 2006 #14
    Often my math teacher would give us tests which consisted of multiple choice questions that we weren't supposed to answer. Instead we were asked stuff like "What mistake would a student who chose option A have made?" and also to use calculus to find the correct answer and do other stuff as well.

    Very good way of teaching to recognise common mistakes in my honest opinion.

    (What is funny is when half the people in the class get to the question which said "Why is A/B/C/D not the answer?" and they go "****, that's the one I would've chose")
  16. Nov 1, 2006 #15
    HAHA I would have laughed too:rofl:
  17. Nov 1, 2006 #16
    The student in question probably absent mindedly put a negative in again after squaring velocity and did not think about checking their math.
  18. Nov 1, 2006 #17


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    Wow! That's a great idea! I might have to incorporate a few like that into future exams. Did he ever get a student that went through and just circled choices? With enough years of teaching, surely there was one student who didn't read instructions and just filled out their multiple guess answers. :biggrin: :devil:
  19. Nov 1, 2006 #18
    Haha well there are big sections of questions in between. (usually 3-4 question per multiple choice). Like we got a multiple choice which was basically "Evaluate such and such an intergral" the questions we got were;

    "Can the value be negative?" - Of course, we're just evaluating, not finding the area under the graph.

    "Use your calculator to evaluate the integral" - The answer was -2 (what was funny is some people said no to the first question then put -2 for this one).

    "Use Calculus to determine the answer" - simple enough.

    "What mistake would someone choosing alternative E: 2, have made?" - Thinking that you can't have negatives, or having the evaluation of the integral the wrong way around (Like having 2 - 0 rather then 0 - 2).

    Also stuff like "What is the derivative of e^(x^2)" and "Why would a student be temped to choose B: 2xe^2x?"

    I think it's really handy way of teaching things, and it helps students to be more aware of stupid little mistakes, which I think is really good because most the time when I get a question wrong it was just some stupid freakin' mistake or miss-thinking that screwed me up. For instance in one test it asked me to evaluate the area under the graph of somethingorother from x = -2 to x = 2 and I for some stupid reason read it as "y= -2 to y = 2"! Luckily I figured out why I was so confused after a while haha.

    Another stupid mistake I did was anti-differentiation and evaluation bit, and I was just about to finish the evaluation when I realised I left out the most important bit, c. So I just added +c on the end of all my lines and of course forgot to multiply the c by 3 along with everything else, so I got c = 12 rather then c = 4. I was the only student to get that far, which was kind of ironic considering I thought the question was kind of easy, and they get better marks then me - because I haven't done a single lick of work since the start of the year. (I literally slept through classes - which wasn't a good idea, but I'm too lazy)

    I'm sorta lucky to get through high school unscathed though, my chemistry teacher wanted to fail me because I did no homework or anything - I did the required work (which are done in SACs in Australia, donno about other places). Just nothing else he wanted me to do. But that's when I got a B on my chemistry mid-year (The highest in the class was B+ only 1, then a few Bs and the rest were Cs, I donno if it was a hard exam or if the class is just stupid) so that ruined his chances of failing me. But he is a cool teacher and we talk a fair bit, he didn't want to fail me because he doesn't like me, just because I did no work and deserved a fail so badly.

    Anyway a ranted on a bit, that's basically my whole life. :P
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