Unit #1

Activity 5
Modeling Microworlds

Activity Overview

Models can be used to help us understand and predict the behavior of super balls and atoms.

Part A: An explanation of how modeling can take different forms is given. Then students play the role of superballs in their first kinesthetic modeling experience.

Part B: Using Workbench software students interact with a computer model of a super ball. They will have the ability to "throw" or launch the ball around the box and be able to modify various properties, such as the mass of the ball, initial speed of the ball, and elasticity of its collision with the walls. Then, using ZoomIt, students zoom in from outer space down through the powers of ten to the atomic level where they find a single atom contained in a box.

Learning Objectives

• Using a computer model, demonstrate the necessary conditions for having an atom/ball not convert any kinetic energy to other forms.
• Predict the behavior of an atom with 100% elasticity that is set in motion.
• Investigate two characteristics which affect the kinetic energy of an object.
• Describe how the motion and mass of an atom correlates with a graph of its kinetic energy.
• Describe two different kinds of modeling, one which is an idea or theory, and one which is something that acts out the idea or theory.

Conceptual Prologue

Macro-Micro Connection

To understand what happens to the hot air balloon (or any other observable phenomenon), students need to be able to think in terms of what is occurring at the atomic level. Throughout this unit modeling will be used to help students visualize the behavior of atoms. Using models is one tool in helping to achieve that understanding.

Science Concepts

Imagine you were in an empty room floating in outer space. Super balls set in motion inside this room would move in a straight line until they collide with something. Each time they collide they would convert some of their energy to other forms of energy, primarily heat and sound. Depending on the elasticity of the super ball, more or less kinetic energy would be converted to other forms of energy. A super ball with high elasticity would take a very long time before it stopped moving.

Atoms and molecules, however, behave as superballs with 100% elasticity! This means that none of their kinetic energy is converted into other forms of energy. A superball with 100% elasticity would bounce around that room forever.

This activity will be the students’ first experience with computer modeling and kinesthetic modeling [using their bodies to act out the rules of a model]. The concept of a model is now extended from the simple representation of an idea or theory to an actual mechanism for testing these ideas. For example, one can have two levels of modeling traffic congestion:

On the idea level, a model could be: Traffic congestion is due to people driving fast enough that they catch up to the person in front of them, causing them to slow down more than necessary resulting in congestion.

On the mechanism level: A computer could simulate this behavior buy having shapes on the screen move according to the rule of accelerating until meeting another shape. This second type of model is a dynamic model which can be used to see if the congestion does actually result from this type of driving behavior. The person setting up the model can now change various parameters like, how many cars, how fast they drive, how many lanes there are, etc.

Students will use computer models and even their own bodies as elements of models to explore how an atom behaves.

Naive Conceptions

• Kinetic energy is only related to velocity.

Kinetic energy is related to both mass and velocity. Often students forget about the mass component of kinetic energy.

• Energy is not conserved.

Energy is conserved. When a superball bounces to a lower and lower height, students often think that it is losing energy. In fact, some of its kinetic energy is converted to other forms, such as heat and sound. The air around the moving ball is warmed as the ball moves through it, the ball and floor are warmed during each impact, and sound is emitted during impacts.*

• Computer models are always "right".

Computer models, like all models of reality, have limitations and flaws. Nothing can behave exactly like reality except for reality. However, we can learn how to make good predictions of how reality will behave.

• The word "model" doesn't have any scientific meaning.

Model, in scientific terms, can mean several things. In this activity the term model is used most loosely to refer to an idea or theory of how something works. A more useful idea of a model which will be explored in later activities is something which based on certain rules can make predictions about various phenomena, like behavior of gasses, the weather, and the economy. Students may hear the word "model" and think: fashion, a good example, a small replica, etc.

*Sound is also emitted as the ball moves through the air, but usually at a level too soft to hear.

Activity Design and Execution

Major Science Concepts:	• Kinetic energy • Conservation of Energy • Dynamic Modeling
Assumed Previous Knowledge:	• Experience with using the ZoomIt software
Time:	• Part A: approximately 30 minutes • Part B: approximately 30 minutes
Materials:	• Popsicle sticks (a box) • Computers with Workbench software
Advanced Preparation: (if any)	• None

Investigative Question: What is modeling and how can it show us the behavior of atoms?

Part A:

1. Remind students about the idea of a model, that a model can represent a theory or idea about how something works.
2. Explain to them that a model can also be something more than just an idea, that a model can be something which follows certain rules described by an idea or theory. Also explain that scientists use models to help them try out various theories and make predictions about natural phenomena.
3. Tell them that today they are going to do "kinesthetic modeling", which will involve them acting like superballs or modeling superballs. Ask them to describe how a person would move if they were pretending to be a superball rolling around in a box lying on a table. List the rules the class comes up with. (They should have things such as: the person should move in a straight line until they hit a wall; the person should bounce off of the walls; the person should slow down a little bit each time they bounce off; the person should convert some of their kinetic energy into other forms of energy; etc.)
4. Set up the class such that most of the students form a square.
5. Have one student be the super ball. Give this student 10 popsicle sticks all facing the same way (remember to color one or both sides of the sticks). This will represent the student's/ball's kinetic energy.
6. Have this student move in a straight line until they collide with a wall and stop. Ask students what should happen to the energy now. They should respond that some of the kinetic energy should be converted to heat energy and given to the wall. Have them hand over one stick to whomever they bump into at the "wall". Then have the student continue on his or her way until they have no more kinetic energy sticks.
7. Try doing this simulation several times but vary how many sticks the student/ball starts with and how much energy is converted during collisions. Ask students to predict what should happen in these circumstances.
8. Tell students that what they just did was a form of modeling called kinesthetic modeling in which they used their bodies to model how a super ball behaves. Have a discussion of modeling using the following questions to frame the discussion:
   • What was this exercise a model of?
   • What were all the pieces of the model necessary for it to work? [Be sure they bring up the rules and the people who were part of the model.]
   • What did you learn from the model?
   • Every model has limitations. What is "wrong" with this model? How does it not behave like a superball?
   • How does this idea of a model differ from your previous idea about models?
9. Then tell them that the computer can also be used to model how balls behave.

Part B:

1. Using Workbench software, have students bring up the "Modeling a Super Ball" activity.
2. The software will then explain the controls and graph to the students (you may also want to demo this on an LCD projector if possible).
3. The software will then ask them to experiment with the various controls and run the model several times.
4. It will ask the following questions
   • In what ways does this model do a good job of simulating how a super ball would behave and in what ways is there “something wrong” with the model that is different from how a superball really behaves?
   • What relationship is there between the length of the velocity vector, the color of the ball, and the kinetic energy depicted in the graph on the right?
   • How does the velocity of a ball affect the kinetic energy of that ball?
   • How does the mass of a ball affect the kinetic energy of a ball?
   • What is the best combination of mass and velocity to get a ball with the highest kinetic energy?
   • Try setting the elasticity slider for various levels and observe what happens to the kinetic energy of the ball. Explain what happens to the kinetic energy using the graph, the velocity vector on the ball, and the color of the atom as examples of why you know the kinetic energy is changing or not.
   • How can you set up the model so that the ball doesn't ever loose any kinetic energy?
5. The software will then pop up a window of the questions and their answer, so you can go over them together.
6. Explain to students that atoms behave just like super super balls, ones that have 100% elasticity. Ask them to predict what they would see if they could see an atom bouncing around in a box. How would it behave, and would its kinetic energy decrease or always stay the same?
7. Have the students use the ZoomIt software to zoom down to a single atom bouncing around in a box. Ask the students to notice how small the atom is and ask them to observe the kinetic energy of the atom. (They should notice that it doesn't decrease.)

Assessment

Have students write several things in their notebooks:

1. What are the two major factors that affect the kinetic energy of an object?
2. On a separate piece of paper write all of the rules you can for creating a model of how an atom behaves. You will be adding more rules to this in later activities.
3. Explain the difference between the type of models that we used today and the type models that we came up with when we described how a hot air balloon might work.
4. If atoms behave like superballs with 100% elasticity and you could directly observe atoms, would they more likely be in motion or standing still? Why?

Internal Notes:
• See Computer Lab A for mock up of Part B of this activity.