A model is a "simplified description of a complex entity or process". It often highlights some feature of the modeled entity or process by blatantly ignoring others. For example scale models of some particular airplane (e.g. XR-71) are faithful in appearance, but can't fly' other models of that same plane can fly but don't look much like an XR-71. Other models are not tangible, e.g. computer models of a nuclear reactor designed to simulate its performancethe supersonic air flow into the engines of the XR-71.
According to David Hestenes, one of the founding fathers of modeling instruction,
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