There are big things on the horizon for Maine science teachers -- big topics, that is. Maine's revised Learning Results contain a new section called Unifying Themes. These larger ideas stretch beyond any one science topic to appear in all areas of science. In our regular featured site-wide segments this year, MSTA will provide a look into each of these unifying themes. We begin our journey with models.

Models are Everywhere

Models are a concept that you and your students students likely use in science every day. But unless you've really stopped to think about it, chances are that you have hardly recognized them. All right, those pretty wooden molecules are certainly models. But that may seem like one of the only times models come to mind. Well, by one basic definition, a model is "any system of objects or symbols that represents some aspect of another system" (Gilbert and Ireton. 2003). In reality, this ends up involving practically everything!

Models are everywhere

So models are truly everywhere. How about some basic categories? We hope you'll agree that models could be split into four basic categories:

Four types of models

• Models that "look like"
• Models that "function like"
• Descriptive models
• Explanatory or causal models

Models that "look like"

Many of the things that come to mind when you hear the word "model" are of this type. A model plane or car contains some physical aspects that are similar to the actual item. A globe does the same thing. All of these examples leave out some features and distort others -- a plane has an engine, cars have working window wipers and the Earth does not actually have different colored countries.

Models that "function like"

Some models aim to work like the things they try to represent. This means they might look pretty ugly, but as we all know, looks aren't everything. (If you need convincing, take a look at Bill Gates...) Models that act like something else help to show how things work or how their pieces relate to one another. You may have seen plastic models of the solar system that show how different planets and moons rotate and revolve, or have seen students build models of how elbows function. These examples can do a good job of showing how things function, their main purpose. Because of this, matching the appearance of the thing they are representing takes a back seat. Portions may be left out, or distances distorted. This is important to remember when using these types of models with students, since students themselves may not realize these differences in appearance.

Descriptive Models

When is a model not a model? Descriptive models often bear no resemblance to the things they represent. Graphs, formulas and tables that measure represent parts of a system are all examples of descriptive models. Graphs may represent stream flow rates, and tables of numbers may represent nutritive values for food, but neither could be said to look like the thing being represented. Because they are efficient, descriptive models can be very powerful, and students should become comfortable with them and know how and when to create and use them.

Explanatory or Causal Models

When scientists want to understand or describe systems, they look for simple explanations that are consistent with the things they observe about the natural world. When we try to explain things that we know is controlled by something we can't directly observe or measure, we naturally search for these types of models. A description of how pollutants get into the ocean or how the inside of a bicycle pump works would usually be an explanatory or causal model. When they observe things in the lab for the first time, your students are almost guaranteed to begin developing explanatory or causal models for what they see. These models are very useful to scientists, and are an important step in the process of constructing complete models of scientific phenomena and processes.

Learning the differences between these models can help you as a teacher decide when to use any one, and how best to help your students make sense of science in the world around them. For more information about these typse of models, consult one of the references below.

References: