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course Phy 202
Tuesday, July 10, 2012, between 11:10 PM and 11:15 PM
The kinmodel experiment states that we're to email our instructor with our preliminary observations before proceeding to the next portion of the experiment. Because a) you've indicated a preference for receiving work via forms and b) using forms is equally compatible with the purpose of sending you our preliminary observations separately and in advance, namely to ensure that they're somewhat predictive rather than entirely descriptive, I'm using the Submit Work Form to send these observations; let me know if you'd prefer that I email them." "Preliminary Observation
Run the program kinmodel, accepting all defaults by using the 'Enter' key to answer the prompts on your computer (the computer will then automatically pick the selection with the asterisk) and observe the particles or 'billiard balls' bouncing around the screen and off one another. ???? I dug out an old Win98 laptop and was able to run the kinmodel.exe program on it. I'm now answering with respect to it, as opposed to the billiard_experiment_006b.exe program. ????
* Watch the KEx and KEy values as they change with each collision, representing the total x and y kinetic energies of the particles.
* Watch the 'red' particle for a couple of minutes, estimating the average time between its collisions and its average speed (one of the speeds given near the top of the screen corresponds to that of the 'red' particle--which is it?).
- - RESPONSE: The 'red' particle's average time between collisions appears to be about the same as for any other particle: Although the 'red' particle is moving more slowly than the average (median or mean) green one, that fact seems not to affect the frequency of collisions. (If it's moving more slowly, it stays out of the way of some particles but gets in the way of others. The lower velocity means that a) particles closer to it at any given point in time are more likely to strike it within a given amount of time and b) particles farther away from it at that time are less likely to strike it within that same time interval, but the likelihood of its being struck by some particle or another is identical. Of the two numbers to the right of the ""Speeds of last 2 molecules:"" text, the left/first is the speed of the red particle. (The right/second is the speed of the blue particle.)
* Watch the 'blue' particle, and speculate on what property of this particle is different from that of the other particles.
- - RESPONSE: The 'blue' particle is more massive than the others; see my earlier comments in Query 6 re: the red ball in the billiard_experiment_006b model.
* Watch as the 'red' particle sometimes turns yellow. What causes this? What property does the particle have when it is yellow?
- - RESPONSE: The color change to yellow, whether in the 'red' particle or in one or more of the 'green' ones, appears to indicate that the yellow particle(s) is/are currently the fastest-moving particle(s) in the model; think of this indicator as analogous to the ""yellow jersey"" in the Tour de France. The particle acquires this status when it is struck by and receives kinetic energy from another particle, usually another fast- (and in a plurality of cases the fastest-)moving particle.
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The 'yellow' condition is that the particle is in a certain range of velocities. The range is pretty high, but it's possible for a particle to exceed that range, in which case it would not change color.
However at that speed the particle would be very hard to identify; it probably wouldn't even register clearly on your retina. So the perception that the yellow particles are the fastest is very reasonable. This hypothesis probably couldn't be tested by the eye, at least not in real time.
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* What might the graphs represented at the right of the screen represent?
- - RESPONSE: The graphs at the right of the screen represent statistical distributions of speeds, with speed on the x-axis and number or percentage of particles on the y-axis. Assuming that the two graphs have the same scale, the red (top) graph is more rightward-shifted (reflective of a higher mean and median speed) than is the light-yellow (bottom) graph. The graphs don't specify whether they represent the various particles' speeds at any given point in time or whether they instead represent a longitudinal (across-time) compilation of mean or median speed at each of various sampled times. One graph could be a ""time-slice"" graph and one a longitudinal graph, or both could be longitudinal, with one a distribution of mean values and the other a distribution of median values. In the latter case, the presence of the slower and more massive blue particle would drag down the mean relative to the median, making a distribution of means have lower mean and median values (be more leftward-shifted) than would a distribution of medians. In that case, the red graph would represent a longitudinal sampling of median values, whereas the light-yellow graph would represent a longitudinal sampling of mean values.
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Good.
In fact, the program simply records the speed of one selected particle with each transition, and increments the corresponding 'bar' on the graph. The graph is also rescaled with every transition.
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* Strike the 'S' key to stop the simulation, and if you are done give the appropriate response to the prompt to quit the program. CTRL-ALT-DELETE will also stop the program, but if you're not careful it will reboot your computer so avoid that option if you can.
Before reading further email your instructor with your best answers to these questions. There are two good reasons for not reading ahead: If you get your answers by reading ahead your instructor will be able to tell, and if you read ahead you won't learn as much.
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&#Good work on this lab exercise. See my notes and let me know if you have questions.
Revision isn't requested, but if you do choose to submit revisions, clarifications or questions, please insert them into a copy of this document, and mark your insertions with &&&& (please mark each insertion at the beginning and at the end).
Be sure to include the entire document, including my notes. &#