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] |
elementary
But if you *do* use a force probe then you can make the lab more
because you no longer have to analyze an Atwood Machine. The pulley andthe
mass at the end of the string are merely a way to apply the force, whichis
measured at the point of application. No need for mg either. The nextstep
is to get rid of the string and just push and pull the cart randomly bythe
force sensor, while logging F and a. Pasco should modify the software sogoing
that the force probe can be calibrated in arbitrary units. For this
experiment you don't want to measure force in newtons.
Related to this, I found something really nice when we were playing with
the Pasco track a few months back. The idea was to show that the
acceleration of a body projected upwards doesn't change as it goes up and
comes down again. The v-t graph should be a straight line, starting with
positive velocity, passing through zero at the top of the motion, and
negative as the body comes down. (Of course a terribly difficult graph toit
predict, sometimes even for people with a lot of basic physics behind
them). So we set the track at an incline and pushed the cart up, letting
come down again, while logging the motion with the little ultrasoundmagnitude
sensor. We got a distinct kink in the graph as it passed through zero
velocity. The acceleration while the cart is going up has bigger
than while it's coming down, and the graph makes two pretty good straight
lines. Assuming that this is because the friction changes sign at the top
of the motion, one can go on to estimate the size of the friction force
from this graph (you also need the mass of the cart). I was struck by how
easy it was to see and measure the effect with the datalogging stuff.
Mark