Re: Kinematics - a vs. t graphs

[Ludwik Kowalski <kowalskil@MAIL.MONTCLAIR.EDU>]

We will start using the motion detectors next week.  Then
 I will investigate the "noise."  As I remember, the plot is
a practically noiseless horizontal line when the detector
faces a wall.

Now suppose the "wall" starts moving slowly toward me.
I suspect that the display will be a stepwise function of x
versus t. The ADC (analog-to-digital convertor) has only
7 bits (?) and this is likely to produce steps. The 9-bits
ADC should display 4 times smaller steps. Ideally the ADC
error should be much smaller than fluctuations on the
analog side. Does anybody know how accurate are
distance measurements on the analog side? What can
be done to reduce them?
Ludwik Kowalski

On Wednesday, September 17, Gary Hemminger wrote:

> "You cannot reliably infer the acceleration from samples
> of the x and t coordinates, not without some nontrivial
> regularization assumptions."
>
> We are using old Vernier software and motion detectors for Workshop
> Physics labs in which we generate d, v, and  a vs. t graphs. The a vs t
> graphs are always noisy, and generally look like the edge of a
> carpenter's saw.  I'm not familiar with the latest software and
> equipment, and wonder if cleaner graphs are now possible.
>
> Despite the difficulties mentioned in the thread above, I expect that
> the main issue here is coming from the propagation of error.  If the
> motion detector takes say 30 readings per second, then I assume that it
> calculates 30 average velocities per second, and uses Ludwik's method
> to find 30 average accelerations per second.  I find that the noise
> varies
> from one machine to another in my room despite similar setups and
> conditions.