Re: Significant figures - a Modest Proposal

[Glenn Knapp <kahuna@VCN.COM>]

>> At 06:03 -0700 8/30/99, Robert A Cohen wrote:

>>

>> >While I'm on the topic, I should mention that I will be emphasizing the

>> >distinction between precision and resolution and that both contribute to

>> >the accuracy of the measurement (I haven't done so in the past).  The

>> >activity above is designed to introduce the idea of resolution and its

>> >effect on calculations.  The second activity is designed to introduce the

>> >idea of precision and its effect on calculations (they time cars and see

>> >how many are speeding - the timer provides measurements to the hundreths

>> >of a second but the precision is not that good).  If anyone has any

>> >experience with teaching this, I'd appreciate pointers.

>> Leigh

I've found that very few of my students know how to properly make a measurement.  I have several meter sticks that I made myself.  The first is a stick that is 1 meter long -- this is given to a student who then is tasked with measuring the length of a board (which only need by less than a meter  in length).  The student gets one number  in the measurement, maybe 0.6 m.  The next meter stick is divided into 10's.  This time the board is 0.57 m long.  The next one is divided into centimeters  -- get 3 numbers in the measurement.  The last one is a standard meter stick.

I also have the student reverse the process.  I provide the measurement and they describe the instrument that made it.  If the length was 105 m,  what type of markings would the tape measure that made it have to have? 

Using photo gates, students often get measurements like "1.23056 m/s".  Because it came from a computer, they consider it to be an extremely precise measurement.  It takes a lot of work to convince them that the accuracy of the measurement really depends on their accuracy measuring the flag that went through the photo gate.

I also agree with you on the use of a stop watch.  Another factor that affects their accuracy is judging when a moving object starts and when it crosses the finish line.  When is an object dropped and when does it actually hit the floor?  All this on top of the reaction time.

Do any of you do the old drop the ruler between the poised fingers demo to determine reaction time?

Glenn

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