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Re: Newton's Second Law Lab



Today John Gastineau described a great experiment to be
performed by those who have Vernier or Pasco equipment.
I was performing the very same experiment today (at a
workshop for teacher conducted by him) and was highly
impressed. It is the most powerful lab-based component
of learning and teaching F=m*a, in my opinion.

On the same screen you see three independent graphs.
One is above, showing F(t); one is below showing a(t).
Both are measured independently (several times each
second) as you are pushing and pulling the platform
back and forth through a forcemeter). The accelerometer
and the forcemeter are connected to a computer which
does nothing beside displaying. The F(t) and the a(t)
curves have identical shapes.

The third graph (on the side) shows the scatter plot
of instant values of F versus a, as they are measured.
The points are scattered near the straight line passing
through zero. (They would form a perfect straight line
if there were no experimental errors.) Jack Uretsky
would love this experiment, if it existed at MIT at
his good young days. Perhaps he would call himself
an experimentalist today.

I also learned at this workshop that the best way
to start using Vernier products today is to get the
LabPro interface (instead of their traditional ULI).
It costs $220. The accelerometer costs $90 and
the force meter costs $100. Aha, and you will need
one more item, the LogerPro software $65, which works
for hundreds different experiments, if you have more
probes. A package with many probes (forcemeter not
included) costs $800; it allows you to perform many
basic experiments.

No, unlike John, I am not associated with Vernier.
And John does not know that I am comosing this to
promote the company. They deserve to be promoted.
Take his hand-on workshop when it is offered again,
somewhere in your area.
Ludwik Kowalski.

John Gastineau wrote:
Use a force sensor and an accelerometer on a cart. Zero both. Start
collecting
data, and grab the hook of the force sensor. Wiggle the cart back
and forth so
that the only horizontal force applied to the cart is through the
force
sensor.

The graph of the acceleration will be the same random shape as the
force
graph, indicating that there is a deep connection between force and
acceleration. Then make a plot of force vs. acceleration. Regardless
of how
the cart was moved, the force vs. acceleration graph is a straight
line
passing through the origin. The slope is the (inertial) mass of the
cart and
sensors. Of course, this then begs the user to add mass to the cart
and try it
again.

The neat thing about doing the lab this way is that you're making
independent
measurements of force and acceleration, AND that you're showing the
second law
for general, time-varying forces, not just constant forces.

My apologies if this idea has already been posted; I'm at a
conference all
week and only have occasional Internet access.

__________________________________

John E. Gastineau john@gastineau.org
953 National Road, #163 (304) 243-9636 voice
Wheeling WV 26003-6440 (304) 243-9637 fax
USA http://gastineau.org
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