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I have some reservations about the mbl experiments for Newton's second law,boxes
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
this may be OK, but I like the students to have some idea of what thesensor
does.too
The force sensor is OK since it works by stretching, and the difficulty is
with the unit only, but I much prefer getting the acceleration
kinematically. Yes, the data can be messy if you "double difference" the
position measurements, but it's easy and quick enough to do straight line
fits to v-t graphs for a series of constant forces, and the graph is not
bad for the experiment that John Gastineau describes below.time
Mark
At 08:56 10-12-98 +0100, John Gastineau wrote:
...discussion of half-Atwood experiment deleted...
only
A much cleaner experiment is possible using a force sensor and an
accelerometer. Attach both devices to a cart; move the cart by hand using
the force sensor. Record both the force vs. time and acceleration vs.
withdata, then plot force vs. acceleration. The points should be on a line
butslope m, where m is the total mass of the cart, accelerometer and forcecomputerized
sensor. Now change mass of the cart. New slope.
This experiment is much, much cleaner than the old half-Atwood method for
doing Newton II. The half-Atwood approach done with MBL is just a
version of a non-computer method.
You can also do this experiment with a motion detector and force sensor,
tothe data quality suffers considerably since you must work with a second
derivative to get the acceleration data, while the accelerometer gives it
you directly.
I can point you to more details if needed.
JEG
Mark Sylvester
UWC of the Adriatic
34013 Duino TS
Italy
msylvest@spin.it