Lab always takes longer than you think...

I just finished this year's Conceptual Physics Summer Institute.  It's always fun to share laboratory ideas, especially the "come and show me" exercises that form the ground state of my courses.  

At the institute, participating teachers did two of these activities - one with motion graphs, one with circuits.  The question I was asked throughout the weekend was, "how long do you spend on these labs in your class?"  And the answer is, for activities that took only minutes for each individual teacher, I generally spend a full week of class.  

Folks were a bit incredulous, I think.  That's a long time for what seem to be simple "worksheets".  Why do they take so long?  I've got two reasons, among others that people can suggest in the comments:

(1) I'm not just expecting students to get answers and experimental results.  For the prediction portion of the lab exercise, I'm expecting thorough justifications in exactly the format and style I've modeled for them.  No shortcuts are allowed - I only allow them to do the experiment once I've checked their prediction for that thoroughness.  

For the experimental portion of the exercise, I expect clear data that stands up to scrutiny.  At least one second of motion detector data that matches the predicted graph.  Properly obtained speeds, masses, or times that match prediction within 20%.  (For most exercises other than resistors-in-series, if they don't match prediction, they redo either the prediction or the experiment.  We don't just say "human error" and move on.  Grrr.)

(2) Teachers - myself included! - oft underestimate the discrepancy between those tasks which we can do on automatic, and those which the students can NOT.  See, even teachers who are unfamiliar with the "come and show me" methodology are familiar with the ideas that underlie the facts and equations used for prediction.  Students are not.  No, not even if you spend 10-20 minutes going over the facts and equations with the students, showing them exactly how they apply to the exact situations they'll be dealing with.  Your class is starting from square one, and the only way for them to advance to [square>1] is through slow engagement.  They must find the right fact - even if sometimes they find the wrong fact and have to try again.  They must use the equation correctly - even if they not only use the equation incorrectly, but they also are using the wrong equation to begin with.

Oh, then consider the data collection process itself!  Making the simple measurements I ask for with motion detectors, photogates, smartcarts, voltmeters, etc. should be a two minute process - 90 seconds to set up, 30 seconds to acquire the data.  I even demonstrate this two minute data collection process for the class.  Yet.  Figuring out the simplest of ideas - like, how do I quadruple the distance this cart travels along a track? - takes forever for an inexperienced student.  Not because they're dumb, not because they're a lazy slacker, but because they are utterly ignorant, ignorant of not just lab equipment uses but of life in general.*  

* My wife found this out the hard way in her ceramics class.  The class had made cylindrical mugs from molds.  She gave everyone string and rulers, and asked them to measure the circumference of the mug so that they could cut a wraparound decoration to the right length.  She was astounded that very few students could even figure out how to make this measurement at all, and that even those who made the measurement got it way wrong.  

I'm in no way intending a negative rant about the danged kids these days!  I'm just making an observation about the reality of our students' practical skills upon entry to our class.  

One of the hoped-for outcomes of a physics (or ceramics) class is that students have gained some kinesthetic experience with how the world works.  Few school courses outside art or science require students to work with their hands.  So don't expect your class to be able to do simple tasks at all quickly.  Everything in lab always, always takes longer than it should.  And that's okay.  It's time well spent.