Models in Science

Science Models Models are an essential and inseparable part of all scientific activity. Scientist use special skills and technique to design and build models that produce insightful, reliable, and useful results.

Why do scientists use models? Models help us understand and talk about things that are too small to see (like DNA) or too large to see all at once (like the solar system). Scientists can manipulate models and use them to see what changes in the real world would look like. Scientists can update models as new information becomes available. Scientists use different modeling techniques to understand processes that are not visible or easily observed. Modeling techniques help study different interactions and behaviors expressed in environments that cannot be manipulated with instruments at the macro and nano scale.

DIfferent models, different needs The models that scientists develop take many different forms. In some cases they are images, physical constructions, mathematical models, computer simulations, etc. Other modeling techniques include statistical methods, computer simulations, system identification, and sensitivity analysis, but also include less complex methods such as the creation of drawings and the construction of three-dimensional physical representations. However, none of these is as important as the ability to understand the underlying dynamics of a complex system. These insights are needed to assess whether the assumptions of a model are correct and complete.

Types of Models: Images Images can help scientists "see" something that cannot actually be seen, such as names or position of things. In some cases they are images that are developed in an effort to picture something unseen, such as the names or position of things. In this model of the solar system, the size of the planets is done to emphasize different properties of the planets, even if the size is not accurate. The planets are visualized as orbiting the sun, they are aligned to demonstrate the order of the planets.

Types of Models: 3D objects Representation of movement, orbits, scale. A good example of this kind of model would be one that represents the Solar system as small plastic spheres that are mechanically moved in such a way as to illustrate the orbits and order of the planets, their color, size and so forth. Demonstrate the physical model if available and have a class discussion of other characteristics present in this model. Discuss what is represented with this model that is not in the image. Discussion could focus on movement (mechanics), time, orbits, size and scale inaccuracies. 6

Computer Simulations Simulations could include drawings or 3D representations, they can be manipulated and react to the input or change of variables. Demonstrate the application and talk about the three types of representations shown, what it means for something to be a drawing vs. 3d, vs. computer simulation. Have them start to generate reasons why you might need to use these models to understand the solar system. This slide will come back later in more depth, it’s only used here to start the discussion.

Mathematical Models Other models are mathematical in nature and depend on algebraic or other kinds of statements to describe a phenomenon or object. Rays of light are good examples, as these can be treated as waves and equations can be developed that describe the properties of waves in great detail. The graphs of the sine and cosine functions are sinusoids of different phases.

Scientists must be able to recognize what aspects of a model reflect reality, and judge the usefulness of that model with consideration to accuracies and inaccuracies. Scientists must be able to recognize what aspects of a model reflect reality, the usefulness of that model with consideration of inaccuracies, and the role of multiple models in building a better picture of a concept, and then be able to identify and deal with divergences between theory and data. The usual approach to model development is to characterize the system, make some assumptions about how it works and translate these into drawings, three dimensional objects, equations or computer simulations.

Drawings 3D objects Computer Simulations Talk about the three types of representations shown, what it means for something to be a drawing vs. 3d, vs. computer simulation. Have them start to generate reasons why you might need to use these models to understand the solar system. This slide will come back later in more depth, it’s only used here to start the discussion. Computer Simulations

What in these pictures is represented accurately or inaccurately about the Solar System? 1 Notes: some possible accuracies and inaccuracies might center around: Size/Scale (not represented correctly because things would be too large, or too small) Manipulation (Things in motion are mobile parts in the model, it helps when we want to study dynamic systems) Interactions (being able to manipulate models, and observing the behaviors) Accuracy (can very large or small things be accurate, to the point of real life representations? cars, airplanes, etc. ) Limitations (trying to model things that take millions of years or happen very very fast, are limitations to study phenomena) Assumptions Realistic (things are orbiting around the sun), Fun, Dimensionality (drawing is 2D, 3d model) Color (Colors can be used to help understand the concepts better) Rigidity (When studying mobile systems, a mobile model may reflect reality better) Try to lead the discussion toward the ways that a 3-D model could be better/more accurate than this one (it might move, it might portray distance between the planets and the shapes of the planets more accurately, it might help you to know when a certain planet will cross another’s path, etc.), and have them write the pros/cons on the board. 2 3

3-D model of Solar System What is represented in this 3-D model? Notes: have the students write the pros/cons of this model on the board in a way that might lead them to think about ways a computer simulation might be better…for instance in order to make calculations about certain things, or to see a more accurate representation of the orbits, time it takes to go around the sun, relatively to other planets, etc. Does it reflect reality, if so, how?

Computer simulations Besides showing you what something looks like, computer simulations show you how that thing acts. Since we can’t control a lot of things in real life, scientists use models to learn how changes in the real world might affect the scientific system. A lot of these systems are very complex, so using a model can help scientists to simplify the systems in order to study them. Notes: make sure the students understand that we’ll be using computer simulations over the next couple of days, so it’s important for them to learn about them. For point one, emphasize that the solar system computer simulation would show you the planets in action, etc. For point two, talk about how this might be used for the solar system model. For point three, emphasize that scientists can manipulate certain parts of the system, one at a time, to experiment for example…

Models discussion Pros Cons Images 3D Model Computer Simulation Compare the pros and cons of the solar system models. Pros Cons Images 3D Model Computer Simulation Talk about Size/scale (not represented correctly because the sun would be too large, etc), Manipulation (things in motion are more helpful than static things, when we want to study dynamic systems), Interactions (being able to manipulate models, and observing the behaviors), Accuracy (can very large or small things be accurate, to the point of real life representations? cars, airplanes, etc. ), Limitations (trying to model things that take millions of years or happen very very fast, are limitations to study phenomena) Assumptions Realistic (things are orbiting around the sun), Fun, Dimensionality, Color, Rigidity ***This would be a good point to have the students fill out pros/cons sheet for the DNA models they have used so far (paper/pencil, beads). If there is time, you should go over the pros/cons for this, trying to lead up to the idea of a computer simulation.***

DNA Discussion What is DNA? Where can it be found? How big is DNA? How do police use DNA to solve crimes? Find out students’ current ideas of DNA: what it is, its size, and where it can be found, and how they think the police use DNA to solve crimes.