1. Comparing Model Environments Module 3
What is the Best Tool?
Comparing Model Environments
Module 3
Start by making a grid on the whiteboard. Excel, NetLogo and Vensim across the top.
Like, Dislike, Comfort Level down the right side.
On chart paper, record in the left-hand column the questions from Slide 6 for easy reference when looking at the various models. Across the top, put the 3 modeling tools – Excel, Vensim and NetLogo. Call this the FreeFall Chart.
Introduce the session by explaining that we will be looking at the three methods of modeling to compare how they represent the same problem.

2. Objectives
Big Idea: Different models can be used to represent the same thing. What model to use depends on its purpose. - AAAS Atlas of Science Literacy, Vol 2
Review the modeling tools used so far and the models observed
Determine the strengths and weaknesses of each of the modeling tools
Evaluate each tool for its usefulness in the classroom
Ask – is there a concept they teach where they use more than one model to help students understand?
Possible answers:
Physical cell models vs. Cell analogy to a city
Physical models of chemicals vs. models using software
Others?
Have participants expand their answers by asking – What are the strengths and weaknesses of each model approach?
Ask “Why do we show the students different models?”. Participants should mention multiple intelligences and multiple representations. The instructor can bring in examples from their own classroom experience to illustrate.
Address the objectives by noting that we are going to explore the three tools we have used in other models with an eye toward learning which model is the “best” to use for a particular concept, class or student.
If participants are interested, the NSTA has a book which expands the modeling concept for Earth Science approaches. The book is somewhat dated but is a good overview for thinking about the use of models in the secondary science classroom.

3. Agenda Review past models and environments
Compare the 3 environments using
Enzyme
Tailgate
Predator – Prey
Discuss possible applications for the classroom
Quickly outline the agenda

4. Quick Review Excel models NetLogo / Agent models Vensim models
Ask participants – what models have we seen using each of these tools
These are the possible models (as the modules evolve this list may change):
Excel – Flipping pennies, stacking cups, interpolation, regression, Boyle’s law, coffee cooling
Netlogo / Agent – Fire, virus, chemical reactions, pollination, NetLogo model library
VenSim – Fire, cockroaches, coffee cooling, models from MVHS website
Then ask –
What do they like / dislike about each tool?
Which would they be most comfortable using in the classroom at the moment?
Which might have the most impact on student learning?
You might want to chart answers so that they can be revisited at the end of the module.

5. Free fall What should students know about free fall?
What might you want a model to show?
What graphs would you like a student to be able to interpret?
Ask the question – what is free fall? Free fall means that you are dropping an object from a certain height. The force that makes it fall is gravity.
Lead the participants in discussion of the questions. Make sure everyone in the room understands the concept.
Have the questions posted on chart paper and chart participant answers
Possible answers:
Students should understand that an object in free fall is continually accelerating at -9.8 m/s2
Independence of vectors
No other forces
Idealized – all objects fall the same way
A model might show how objects fall with different accelerations or different initial velocities.
Position and velocity graphs showing different starting positions, different initial velocities and different accelerations.
Illustrate the expected graphs – position vs. time is half of a parabola, velocity vs. time is a line with a negative slope

6. Free Fall – Excel Model Open FreeFall.xls
Explore the model using the sliders and buttons
What does the model show?
Does the model address the knowledge student should understand about free fall?
Does the model extend student skills in graph interpretation?
Does the model have any obvious weaknesses?
Look under the hood. How is the model constructed?
Have participants open the Excel Free Fall model and explore it briefly.
Point out the sliders and the radio buttons – use them to explore various scenarios
Then solicit answers to the questions on the slide (Write answers in the Excel column of the Free fall Chart)
Have participants refer back to the concepts they charted to answer the second question.
Question 4 – The vertical height can go negative – should the model use an if - then construct to zero out negative results?
The user might want modify the model to input his/her own values for gravity, or plot multiple heights on the same graph.
Question 5 – Note that there are long columns of calculations on the left. These can be hidden for student use.

7. Free Fall – VenSim model
Open FreeFall.mdl
Explore the model using the sliders
What does the model show?
Does the model address the knowledge student should understand about free fall?
Does the model extend student skills in graph interpretation?
Does the model have any obvious weaknesses?
Look under the hood. How is the model constructed?
Compare this model to the Excel model
Have participants open the model and explore it with the sliders
Lead a discussion of the questions and chart answers in the Vensim column of the Free Fall Chart
Again – have the participants refer to their charted ideas from slide 5 to answer question 2
Question 6:
Three obvious differences
There are only 3 possible accelerations in the Excel model – but the VenSim model allows for a range of accelerations
There are two graphs in the Excel model and acceleration is not graphed. In the VenSim model, there is one graph, but all three values are plotted on it. This requires different interpretation skills. Go over the three scales on the y-axis and how to read them.
The programming is basic algebra – not too hard to setup

8. Free Fall – NetLogo Model
Open FreeFall.nlogo
Explore the model using the sliders
What does the model show?
Does the model address the knowledge student should understand about free fall?
Does the model extend student skills in graph interpretation?
Does the model have any obvious weaknesses?
Look under the hood. How is the model constructed?
Compare this model to the Excel and VenSim models
Have participants open the model and explore it with the sliders
Lead a discussion of the questions
Again – have the participants refer to their charted ideas from slide 5 to answer question 2
Also chart answers in the NetLogo column of the Free Fall Chart
Question 4
One obvious weakness – for certain velocities – the blue object doesn’t quite hit the ground
Question 5
Note the specificity of the commands to ensure the physical model is consistent
Question 6
This model doesn’t allow changes in acceleration – all three objects have the same acceleration (how do you know? – slopes of velocity graphs are identical)
This model actually lets the user see the objects in motion
There are two graphs, but they show a comparison of the motion of three objects at once.
NetLogo has the visual display of the object falling that the other models lack.
NetLogo specific question – remind the participants that when they first saw NetLogo – it was pointed out that each run of the model, for the same initial settings, could produce different outcomes, because the models are usually based on probability and randomness. Was that the case in this model?
(no)
Ask them to watch for this in the models that will be looking at.
NetLogo models are good introductory models to use before Vensim or Excel because of the visual display that allows the student to see the motion.

9. Free Fall – Comparison Which is best?
Which would you be inclined to use in your classroom?
Would you use another model with certain changes? What would those be?
Participant responses will vary.
Q1: It depends on the students and the learning goals.
Q2: Reflect on your own classroom.
Q3: Already discussed in each version.

10. More examples to compare
Tailgate
Another physics example
Initially appeared in The Physics Teacher as an Excel model
Predator – Prey
Common model
This particular version – prey is mice and predator is owl
Enzyme
Began as an exercise during a summer workshop
Explain that in a moment the group will divide to explore one concept presented in three different models. Quickly identify the three concepts.
Might want to have copies of the Tailgate article available.
May want to distribute copies of the enzyme article comparing the three or wait until after the group presentations. Enzyme group can look at two different VenSim models.
Explain to participants how to find the files.

11. What to compare?
Be sure to note how multiple runs with the same setting behave in each version
Compare output of each model – how are the graphs the same? Different? Any other output?
What variables are available?
What is realistic? What needs “fixing” in each model?
Look under the hood. How is the model constructed?
Go over these questions with the entire group before moving on.
A handout with the questions and pictures of the 3 models is available for groups to organize their thoughts around.

12. Comparing models Divide into 3 groups
Each group compare three models for one concept
Chart
What the models illustrate
Strengths and weaknesses of each version
Stand and deliver / gallery walk
Have each participant choose one of the three concepts – Tailgate, Predator-prey or Enzyme. Re-group so that those who are exploring the same concept are in proximity to each other. Give the participants minutes to explore the three available models for their concepts and chart the strengths and weaknesses of each model. Check in with each group to make sure that they understand the purpose of the model and are comfortable with the science behind it.
Allow about 5 minutes for the stand and deliver period.
Refer to the Model Comparison Guide for the Instructor for possible ideas to help participants as they compare models and create their charts.

13. What to compare?
Be sure to note how multiple runs with the same setting behave in each version
Compare output of each model – how are the graphs the same? Different? Any other output?
What variables are available?
What is realistic? What needs “fixing” in each model?
Look under the hood. How is the model constructed?
Keep this slide posted while the groups are working.
After the comparison charts are made, have the groups post their charts for a gallery walk OR ask each group to present their findings to the entire class.
Findings:
Agreed that showing all three versions to students is a good idea. Start with NetLogo and then move to Vensim and Excel.

14. Reflect and evaluate Revisit thoughts from beginning of session
What do they like / dislike about each tool?
Which would they be most comfortable using in the classroom at the moment?
Which might have the most impact on student learning?
Do you feel you have a better idea about the uses of each tool?
Which tool(s) do you want more information about?
Lead a discussion – referring to the chart begun at the beginning of the module
Inform participants that the second group of modules will take them deeper into each of the tools and close with a session where they can build a simple model in each tool as well as build a model of their choice in the tool of their choice.
If participants don’t mention it, bring up that every modeling tool has trade-offs. Each tool has both limitations and strengths.

15. Classroom use
How will you use what you have learned in your classroom?
How will you use this to help students?
Lead a discussion – participant answers will vary.