Chapter 4.8 - Real World Models

Time Estimate: 45 minutes

4.8.1. Introduction and Goals

In this unit, we have learned a number of important factors for building and using models.

• abstraction is used to remove extraneous details and focus the model on essential aspects of the problem.

• pseudorandomness is used to model events, such as coin flips

• plan what the model represents and how it accomplishes that representation

• consider how the model can be used for making and testing hypotheses

Learning Objectives: I will learn to

• describe the benefits of creating models and simulations

• compare and contrast models to identify the strengths and weaknesses of each

Language Objectives: I will be able to

• make hypotheses and predict outcomes of a simulation as well as describe experiment results

• use target vocabulary, such as model, simulation, and hypothesis to discuss how computers can mimic the real world, with the support of concept definitions and vocabulary notes from this lesson

4.8.2. Learning Activities

Model 1 Video | Model 2 Video | Model 3 Video | POGIL worksheet

Solar System Models

Models and simulations are most useful when real-world events are impractical for experiments (e.g., too big, too small, too fast, too slow, too expensive, or too dangerous). Watch the following videos, paying particular attention to the different ways in which the models abstract away certain details from the real world situations that are being modeled. Discuss with your classmates which features of the solar system each model chose to include and to exclude. How do those choices align with the educational goals of each model?

Bill Nye's Model

Bill Nye illustrates the problem of trying to build a scale model of the solar system by using his bicycle to demonstrate the relative sizes and the relative distances between the planets.

7-Mile Long Scale Model

Starting with an Earth the size of a marble, these folks built a full-scale model of our solar system across 7 miles of Nevada desert.

Second Life 3D Model

This solar system model is built in Second Life, on online virtual world. Think about the differences between this model and the others.

POGIL Activity for the Classroom (30 minutes)

Break into POGIL teams of 4. Each team member should take the following roles. Record your answers using this worksheet. (File-Make a Copy to have a version you can edit.)

Role	Responsibility
Facilitator	Records the teams predictions and observations.
Spokesperson	Reports the teams results and conclusions.
Quality Control	Validates the team's results and conclusions.
Process Analyst	Keeps track of the teams progress and assesses its performance.

This simulation of rabbits and wolves shows how nature attempts to stay balanced. Read the Learner's Tab about how the simulation works and then complete the following activities. (Note that this simulator works best in the Firefox browser).

1. On the Activity tab, click Start Simulation. You can open the population graphs at any point to see how they change over time. Record your groups observations about how the population of rabbits and wolves changed over time.

2. Hypothesis: What would happen if there were lots more bunnies than there were wolves? Would the bunnies take over and live forever? Experiment: Test the hypothesis by first resetting the simulation. Then click the View/Modify Parameters button followed by the View/Modify Start Parameters (Note that the View/Modify parameters button does not currently work in Chrome, but does work in Firefox). Adjust the settings to increase the initial number of rabbits. Record your observations. Did your prediction match with the results? How was it different than the first run of the simulation?

3. (Portfolio) Reverse the hypothesis: What would happen if there were lots more wolves than there are bunnies? Would the wolves live forever? Record your hypothesis, prediction and experiment results. (Don't forget to reset the simulation before changing the parameters.)

4. Explain how the rabbits and wolves live in balance in this simulation.

5. (Portfolio) This model chose to include certain features and exclude other features. For example, this simulation only includes rabbits, wolves, and grass but there are other predators of rabbits and other food sources for rabbits. Why do you think the creators focused on these data elements and not others? How might this introduce bias (concentration on or interest in a particular area) into the simulation?

4.8.3. Summary

In this lesson, you learned how to:

Learning Objective AAP-3.F.a: For simulations: a. Explain how computers can be used to represent real-world phenomena or outcomes.

Learning Objective AAP-3.F.b: For simulations: b. Compare simulations with real-world contexts.

4.8.4. Still Curious?

Here are a couple of interesting simulation and modeling examples:

• What if the Moon was 1 pixel is an interactive scale model of the solar system based on the assumption that the moon is 1 pixel. It really captures the idea that space is mostly empty.

• Rapunzel's Hair is a physics-based simulation model of Rapunzel's hair. This work was done by Trinity CS alumna Kelly Ward (PhD, UNC), who currently is a senior software engineer at Disney.

• The Scale of the Universe is an interactive model of that provides a sense of the relative size of different objects in the universe — DNA, earthworms, states, planetary moons, nebula, etc.

• Here are some more sample models and simulations including a similar sheep/wolves model.

4.8.5. Sample AP CSP Exam Question

Q-1: Which of the following statements describes a limitation of using a computer simulation to model a real-world object or system?

A. Computer simulations only run on very powerful computers that are not available to the general public.

B. Computer simulations usually make some simplifying assumptions about the real-world object or system being modeled.

C. It is difficult to change input parameters or conditions when using computer simulations.

D. Computer simulations can only be built after the real-world object or system has been created.

4.8.6. Reflection: For Your Portfolio

Answer the following portfolio reflection questions as directed by your instructor. Questions are also available in this Google Doc where you may use File > Make a Copy to make your own editable copy.