Unobservable Scales and Mechanisms – Scale, Proportion and Quantity in Middle School

January 4, 2020 2 Comments

I first ran across the terms “unobservable scales” and “unobservable mechanisms” early in my NGSS journey.  I had no idea what these were. Unfortunately, a  Google search didn't provide any answers.  Read this post to find out what the terms unobservable scales and mechanisms mean in the NGSS.

Where do these terms appear in the NGSS?

The term “unobservable” appears in the Science and Engineering Practice Developing and Using Models.  In Appendix F of the Standards, the following components of the practices mention the term “unobservable”:

  • Develop a model to describe unobservable mechanisms.
  • Develop and/or use a model to generate data to test ideas about phenomena in natural or designed systems, including those representing inputs and outputs, and those at unobservable scales.

Four different performance expectations include the term “unobservable mechanisms.”

  • MS-LS1-7. Develop a model to describe how food is rearranged through chemical reactions forming new molecules that support growth and/or release energy as this matter moves through an organism
  • MS-PS1-5. Develop and use a model to describe how the total number of atoms does not change in a chemical reaction, and thus, mass is conserved.
  • MS-PS3-2. Develop a model to describe that when the arrangement of objects interacting at a distance changes, different amounts of potential energy are stored in the system.
  • MS-ESS2-4. Develop a model to describe the cycling of water through Earth’s systems driven by energy from the sun and the force of gravity.

What are unobservable scales?

In elementary school, students make observations on the observable scale.  I often refer to this as the person-level because these are things that can be observed with the human eye.  For example, let's look at plant structures.  Elementary students will likely focus on components like the roots, stem, and leaves.

However,  middle school, students are asked to make observations at unobservable scales.  These are the microscopic and macroscopic scales.

I tell my students that microscopic refers to anything that can be seen with a microscope and everything smaller.  These are things that are very, very small.  I include things like atoms and molecules here.  Macroscopic relates to something that you can see with your telescope.  For example, planets exist at the macroscopic scale.  I also tell them that this includes things that are too large to see with a simple telescope, like the galaxy or universe.

Scale doesn't just refer to size or space.  Also,  time scales are also mentioned in NGSS.  For example, geological processes often occur at scales that are to slow to observe with the human eye.

Scientific Notation and Scale – An 8th Grade Math Tie-in

You likely are aware that this isn't the most accurate definition of the terms micro and macroscopic.  I could distinguish between microscopic and atomic-level.  However, I have found that students in middle school struggle with this distinction.  Students learn scientific notation in their 8th-grade math classes.  It is easier for students to quantify scale after they have learned this concept in their math class.

What are unobservable mechanisms?

In each of these performance expectations mentioned above, the Crosscutting Concept is Energy and Matter, except MS-PS3-2.  For this performance expectation, the Crosscutting Concept is Systems and System Models.  However, the subcomponent on the concept focuses on the flow of energy in the system.

Students in middle school should understand that energy provides mechanisms for observable changes, even if the energy can't be directly observed.  Students in this grade band make connections between observable and unobservable scales.

What questions do you have about the term “unobservable” in the Next Generation Science Standards?  Comment below! 

Want to learn more?

To learn more about modeling in middle school, check out these posts:

Erin Sadler

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  • Angela January 4, 2020 at 3:15 pm

    Thank you for sharing this information!!

    • Erin Sadler January 5, 2020 at 11:58 am

      You are so welcome. I hope it was helpful. It’s kind of obscure and difficult to explain.

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