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For both designed and natural systems, conditions that affect stability and factors that control rates of change are critical elements to consider and understand.

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Below is the progression of the Crosscutting Concept of Structure and Function, followed by Performance Expectations that make use of this Crosscutting Concept.

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Tracking energy and matter flows, into, out of, and within systems helps one understand their system’s behavior.

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Below is the progression of the Crosscutting Concept of Systems and System Models, followed by Performance Expectations that make use of this Crosscutting Concept.

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In considering phenomena, it is critical to recognize what is relevant at different size, time, and energy scales, and to recognize proportional relationships between different quantities as scales change

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Events have causes, sometimes simple, sometimes multifaceted. Deciphering causal relationships, and the mechanisms by which they are mediated, is a major activity of science and engineering.

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Observed patterns in nature guide organization and classification and prompt questions about relationships and causes underlying them.