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Practices of Science: Using Models

NGSS Science and Engineering Practices


SF Fig. 2.12. A model of a sodium atom

Image by Alyssa Gundersen

Science is about understanding the natural world. Building this understanding involves making and testing predictions, making observations, analyzing data, and drawing conclusions. Another important aspect of understanding the natural world is communicating scientific knowledge with others. Some parts of the natural world are easy for people to observe, such as different types of clouds in the sky or different kinds of shells on the beach. To communicate about clouds or shells, scientists can use photographs or drawings, sometimes in combination with descriptive words.



SF Fig. 2.13. A model of the solar system

Image courtesy of Nasco

Other aspects of the universe are more difficult to describe. Models are used to represent aspects of the natural world that are too small, large, complex, or difficult to observe or explain directly. For example, atoms are too small to observe directly, so models are used to visualize parts of atoms (SF Fig. 2.12).


Other things, like the solar system, are so expansive that they may be observed a bit at a time, but not all at once. In these cases, models make aspects like scale in a large system easier to visualize (SF Fig. 2.13).


Complex systems, like ecosystems, require an incredible amount of detail to fully describe. Models simplify complex systems to make them easier to understand (SF Fig. 2.14).


Image caption

SF Fig. 2.14. A model of an aquatic ecosystem, the Kaloko reef ecosystem on the island of Hawai‘i.

Image copyright and source

Image courtesy of Colette Wabnitz; adapted from National Oceanic and Atmospheric Administration (NOAA)

No one has seen the core of the earth, yet scientists have gathered sufficient evidence to be able to describe the layers of the planet, as modeled in SF Fig. 2.15.



SF Fig. 2.15. A model of the earth, showing the layers of the earth

Image adapted from Wikipedia

In these, and in many more instances, scientists use models to communicate scientific knowledge.


All models have two key features: (1) models provide a simplified, concrete way of representing a physical entity or an idea, and (2) models are able to provide explanations and allow a user to make testable predictions. Models can take many forms, including diagrams, three-dimensional models, and computer models. For example, the diagram in SF Fig. 2.12 shows a model of a sodium (Na) atom. This model simplifies the complex structure of an atom, while accurately representing the number of electrons in the atom and the energy levels of those electrons. Using this model, scientists can predict the configuration of electrons if one electron were lost or gained.



SF Fig. 2.16. A model of a sodium atom (A) alone and (B) as part of a network of sodium chloride ions

Images by Byron Inouye

Although models allow scientists to represent ideas and make predictions, models also have drawbacks that must be understood in order to use them effectively. For example, a model may be very effective at representing one aspect of a concept, but not as effective at representing a different aspect. For example, the model of the sodium atom accurately depicts the number of electrons, but not the number of protons or neutrons. Different types of models can convey the same idea, and may be appropriate in different situations. For example, when representing a sodium atom as part of a network of ions in sodium chloride, the detail shown in SF Fig. 2.12 would be overwhelming. In this case, representing a sodium ion as a purple circle, as in SF Fig. 2.16, is more appropriate.


The model of the solar system in SF Fig. 2.13 effectively shows the scale of the planetary bodies, but is not effective at conveying the distance between the planets and the sun. In SF Fig. 2.14, the model of the ecosystem is able to represent large ideas, but not details about the components of the ecosystem. The model of the earth in SF Fig. 2.15 represents the scale of the layers of the earth, but does not show any details about the composition of those layers.


In general, models help scientists represent concepts that are difficult to see easily.  Models assist scientists in making predictions. However, scientists must be aware of the advantages and disadvantages of every model in order to use models effectively.

Exploring Our Fluid Earth, a product of the Curriculum Research & Development Group (CRDG), College of Education. University of Hawaii, 2011. This document may be freely reproduced and distributed for non-profit educational purposes.