Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: Newton's 2nd law Lab



-----Original Message-----

[mailto:PHYS-L@LISTS.NAU.EDU]On Behalf Of Mark Sylvester

I have some reservations about the MBL experiments for Newton's second law,
and wonder if they are shared.

Minor reservation: I don't like using a force sensor already calibrated in
newtons when we want to show the second law.

Bigger reservation: I don't like using an accelerometer which works by
inertia for this experiment. If we treat the sensors strictly as black boxes
this may be OK, but I like the students to have some idea of what the sensor
does.


If you treat the force sensor like a spring scale, and begin by defining force
as "what the spring scale (or force sensor) measures" then Mark's first issue
is less significant. The NII experiment then reveals an interesting
correlation between what the force sensor measures and the observed
acceleration.

Mark has a good second point here, but the accelerometer is a very useful
sensor. One way to make the accelerometer less of a black box is to do a
preliminary experiment using a motion detector and the accelerometer. Measure
the acceleration of a cart on a ramp using both sensors. The kinematical
calculation of acceleration from motion data should be easily understood by
students, and that the accelerometer data corresponds directly will
demonstrate clearly what this new sensor is measuring. This preliminary
experiment need be done only once, and serves as an introduction to numerous
other experiments.

(If you try this experiment, be sure to zero the accelerometer while the cart
is at rest but on the ramp.)

JEG

__________________________________

John E. Gastineau john@gastineau.org KC8IEW
900 B Ridgeway Ave. http://gastineau.home.mindspring.com
Morgantown WV 26505 (304) 296-1966 voice (304) 296-5035 fax
USA