Re: Interactive Physics graphing...

[gastineau@badgerden.com (John E. Gastineau)]

about IP graphing:

The default graphical display in IP is potentially confusing since 
it does an autoscale every time the data trace goes offscreen. It's 
easy to lose track of where the zero-velocity spot is on the vertical 
axis. Once I know what range of values a graph will need, I think 
it's helpful to the class to turn off the autoscaling. 

Or, could it be that rather than asking IP to display a velocity
graph you asked for a speed graph? Then you'd get a vee-shape.
Otherwise, with no air resistance you'd get the expected line of
constant negative slope. 

As far as a scale, you can ask IP to display a numerical scale as you 
like. Double-click on the graph to adjust its settings. 

All that's in the manual, of course. But here's a suggestion that
I've used a number of times in my simulations in class. I got the
idea from a simulation that Bob Beichner did several years ago, and
developed it in to a simulation that has been  a wonderful in-class
exercise in my intro classes. 

In Arnold Arons' book on intro physics teaching he suggests
considering  the following situation: A ball is bouncing on the 
floor. It bounces three times, each time rising a little less high. 
Sketch graphs of the ball's position, velocity and acceleration as a 
function of time. 

Most classes have a hard time doing these sketches. I programmed IP
to do the bounce, then the bounce with a y-position graph. Bob
Beichner's idea is position a large y-position graph right next to
the ball, with the graph stretched so that an inch of ball travel is
represented by an inch of y-axis scale. Then it just jumps at the
class that there is a correlation between the graphical
representation and the physical travel of the ball. 

(A feature of IP that few people seem to know about is that you can 
resize a graph by dragging the corners, and that you can get rid of 
the ugly borders and add axes with scales in the properties and 
appearances dialog boxes. I wish the default graph appearance were 
different. Perhaps version 3 of IP, which is supposedly on its way to 
me now, will be better.)

Of course, the next steps are to ask the class to sketch the velocity 
graph. (Be sure every student completes a sketch first. ) And you can 
fill in the rest. 

I challenged a group of physicists at an AAPT meeting to do this task 
a while back. The results were, well, amusing. 

JEG


Oh yes--these an other simulations are still on the ftp site I used 
while at NCSU-- check out ftp.pas.ncsu.edu, and look in the pcep_out 
directory. They are intended for in-class discussion starting use. 








> 	Greetings.  Today I was showing our school's math teacher the 
> Interactive Physics 2.5 that is on one of the school computers.  I was 
> helping him to understand as to what happens when you throw a ball straight 
> up.  I had the simulation keep track of the ball (position, velocity, and 
> acceleration) on the Y-axis.  My first question is when I switch to 
> graphing the ball and it's showing the position, velocity, acceleration, 
> the velocity line does not seem right.  I noticed this when the ball 
> reached its highest point and started coming back down, the velocity line 
> did not seem to reflect the change of the velocity.  Am I right about 
> what is being displayed for an object rising and falling?
> 	My next question is if it is possible to put a scale to the 
> graph.  The graph gives an idea as to what is happening, but it would be 
> nice to set it to a scale.
> 	Finally, is it possible to set up a table of each increment that 
> goes by.  For example is it possible to set up a data table (position, 
> velocity, acceleration, etc.) for each one second interval?
>
> 	Any information that someone has would be greatly appreciated.  I 
> know there has to be a manual somewhere, but unfortunately I'm new there 
> and the teacher responsible for putting it on is no longer around.
>
> Thanks,
> Dwight
> dsouder@ashland.edu
-=================
John E. Gastineau
304 296 1966
Morgantown, WV 
http://www.badgerden.com/~gastineau
email: gastineau@badgerden.com   <==== NEW as of 10/1/96