Reflections on our first physics practicum

We are currently in the later part of our Constant Velocity Particle Model (CVPM) unit in my physics class.  So far, we have developed 4 models that only represent one particular type of motion, constant velocity.

• position-time (x-t) graphs
• velocity-time (V-t) graphs
• motion maps
• equation (Xf = Vt + Xi)

Throughout the development of these models, I constantly try to remind my students why it is that we're even building them in the first place.  Without going into too much detail in this post, my explanation revolves around the idea that in all fields of science, we rely on models to make predictions about reality and eventually better understand it.  If reality conflicts with our models that we make, then something must either be modified about the model or the entire model itself must be thrown out.  Models, if they are correct, essentially allow us to predict the future in addition to allowing us to deepen our understanding of how the universe works.  

So.....we put our models to the test!!  My challenge to them was short and sweet

Determine how long it will take for your buggy (car) to go from one position to another.  You cannot perform any practice trials.

I provided them with 2 bits of info and tools to help them gather data
Info:

• I gave each group an initial and final position (Xi and Xf)

Tools:

• Vernier motion detectors and a computer with Vernier's LoggerPro software

Based on our previous work with position-time graphs, several students caught on to the idea that maybe they should use the motion detector to come up with a position-time graph for their car.  Because they needed velocity to solve for the amount of time it would take to go from A to B, they knew all they needed to determine was the slope of their position-time graph.  Once that idea buzzed around the room, I told groups that they should probably perform 3-4 trials each in order to get a more accurate determination of their velocity.

Once each group had their velocity, I required them to make 4 things:

1. A quantitative position-time graph describing the motion of their car
2. A quantitative velocity-time graph describing the motion of their car
3. A quantitative motion map describing the motion of their car
4. An equation that is solved with their work shown so that I can see how their time was calculated

When they were finished with that, then it was time to test their models!  I connected 3 big whiteboards and made a position line that extended roughly 3m with intervals of .1m throughout.  Because groups had been given an initial and final position (each group had different ones by the way), they knew where to start their car.

The actual setup was simple.  Place your car at its starting position, place my iPad with the stopwatch up on one side of the position line, and I'll video tape the finish line in slow motion (120 fps) with my iPhone.  This allowed us to actually see what time the car crossed the finish line (their final position).  The results were great!!!  EVERY single group got within .6 sec of their predicted time and one group even made a PERFECT prediction!!  I've provided a couple samples below:

I took a screenshot so that you could see how much time passed by when their car crossed the line:

As you can see, their final position was 1.3 m.  What was their predicted time?????

5.80 seconds!!!!

This was so cool because not only was I excited about their result but I immediately saw the smile on their faces.  The members of this group were not your typical "do-gooders" in school and yet they made the best prediction in class!

A different group had a different car show below:

 Again, here is snapshot of their car crossing the finish line (2.7m) and its corresponding time

This group's predicted time was 4.21 seconds......awesome!!!

In the end, all 7 groups made awesome predictions and several of them were within .09 sec of their predicted time.

This practicum provided 2 important things:

1. It told us that our models accurately represent reality--at least with respect to constant velocity.  AWESOME
2. It was fun!  The kids had a fun time gathering around the whiteboard track and closely watching their car make its run.  Once groups had gone, they stuck around and watched other groups and it sort of naturally became a competition to see who made the best prediction.

This was so cool because it gave my students an opportunity to learn science by actually doing science.  Gather your data, make your models and test your models against reality.  Boom!

I will be doing another practicum next week where I give each group a specific time interval and an initial position and they have to tell me (based on their models) where their car will be at that time.  Can't wait to see the results!