This unit builds toward these performance expectations:

• HS-ESS1-4 Use mathematical or computational representations to predict the motion of orbiting objects in the solar system.
• HS-ESS1-6 Apply scientific reasoning and evidence from ancient Earth materials, meteorites, and other planetary surfaces to construct an account of Earth’s formation and early history.
• HS-PS2-4† Use mathematical representations of Newton’s Law of Gravitation and Coulomb’s Law to describe and predict the gravitational and electrostatic forces between objects.
• HS-PS3-1† Create a computational model to calculate the change in the energy of one component in a system when the change in energy of the other component(s) and energy flows in and out of the system are known.
• HS-PS3-2† Develop and use models to illustrate that energy at the macroscopic scale can be accounted for as a combination of energy associated with the motion of particles (objects) and energy associated with the relative positions of particles (objects).

†This performance expectation is developed across multiple courses.

ESS1.B: Earth and the Solar System

• Kepler’s laws describe common features of the motions of orbiting objects, including their elliptical paths around the sun. Orbits may change due to the gravitational effects from, or collisions with, other objects in the solar system. (HS-ESS1-4)

ESS1.C: The History of Planet Earth

• Although active geologic processes, such as plate tectonics and erosion, have destroyed or altered most of the very early rock record on Earth, other objects in the solar system, such as lunar rocks, asteroids, and meteorites, have changed little over billions of years. Studying these objects can provide information about Earth’s formation and early history. (HS-ESS1-6)

PS2.B: Types of Interactions

• Newton’s law of universal gravitation and Coulomb’s law provide the mathematical models to describe and predict the effects of gravitational and electrostatic forces between distant objects. (HS-PS2-4)
• Forces at a distance are explained by fields (gravitational, electrical, and magnetic) permeating space that can transfer energy through space. Magnets or electrical currents cause magnetic fields; electrical charges or changing magnetic fields cause electrical fields. (HS-PS2-4),(HS-PS2-5)

PS3.A: Definitions of Energy

• At the macroscopic scale, energy manifests itself in multiple ways, such as in motion, sound, light, and thermal energy. (HSPS3-2) (HS-PS3-3)
• These relationships are better understood at the microscopic scale, at which all of the different manifestations of energy can be modeled as a combination of energy associated with the motion of particles and energy associated with the configuration (relative position of the particles). In some cases the relative position energy can be thought of as stored in fields (which mediate interactions between particles). This last concept includes radiation, a phenomenon in which energy stored in fields moves across space. (HS-PS3-2)

PS3.B: Conservation of Energy and Energy Transfer

• Energy cannot be created or destroyed, but it can be transported from one place to another and transferred between systems. (HS-PS3-1),(HS-PS3-4)
• Mathematical expressions, which quantify how the stored energy in a system depends on its configuration (e.g., relative positions of charged particles, compression of a spring) and how kinetic energy depends on mass and speed, allow the concept of conservation of energy to be used to predict and describe system behavior. (HS-PS3-1)
• The availability of energy limits what can occur in any system. (HS-PS3-1)

Developing and Using Models: This unit intentionally develops students’ engagement in this practice element:

• 2.3 Develop, revise, and/or use a model based on evidence to illustrate and/or predict the relationships between systems or between components of a system.

Analyzing and Interpreting Data: This unit intentionally develops students’ engagement in this practice element:

• 4.1 Analyze data using tools, technologies, and/or models (e.g., computational, mathematical) in order to make valid and reliable scientific claims or determine an optimal design solution.

Using Mathematics and Computational Thinking: This unit intentionally develops students’ engagement in this practice element:

• 5.2 Use mathematical, computational, and/or algorithmic representations of phenomena or design solutions to describe and/or support claims and/or explanations.

The following practices are also key to the sensemaking in this unit:

• Asking Questions and Defining Problems
• Planning and Carrying Out Investigations
• Constructing Explanations and Designing Solutions
• Engaging in Argument from Evidence
• Obtaining, Evaluating, and Communicating Information

Scale, Proportion, and Quantity: This unit intentionally develops students’ use of these crosscutting concept elements.

• 3.1 The significance of a phenomenon is dependent on the scale, proportion, and quantity at which it occurs.
• 3.2 Some systems can only be studied indirectly as they are too small, too large, too fast, or too slow to observe directly.
• 3.5 Algebraic thinking is used to examine scientific data and predict the effect of a change in one variable on another (e.g., linear growth vs. exponential growth).

The following crosscutting concepts are also key to the sensemaking in this unit:

• Patterns
• Cause and Effect: Mechanism and Prediction
• Systems and System Models
• Energy and Matter in Systems: Flows, Cycles, and Conservation
• Stability and Change of Systems

Which elements of NOS are developed in the unit?

• Scientific Investigations Use a Variety of Methods. Science investigations use diverse methods and do not always use the same set of procedures to obtain data.
• Science Models, Laws, Mechanisms, and Theories Explain Natural Phenomena. Laws are statements or descriptions of the relationships among observable phenomena.
• Science Models, Laws, Mechanisms, and Theories Explain Natural Phenomena. Models, mechanisms, and explanations collectively serve as tools in the development of a scientific theory.

This unit is anchored by a montage of video clips showing a fireball over Chelyabinsk in Siberia in 2013 that caused millions of dollars in damage and thousands of minor injuries, although thankfully nobody was killed. This phenomenon provides the context in which to investigate forces at a distance, energy transfer, and the mechanics of orbits, including Kepler’s laws and Newton’s universal law of gravitation. By the end of the first lesson set, students will be able to explain how different strategies of meteor deflection to protect Earth from meteor impacts work. Based on field-test data and our own tests, this phenomenon will also elicit questions about the likelihood of similar events happening in the near future. To answer these questions, students will explore multiple data sets of empirical evidence about the surface of Earth and other space objects to investigate how the frequency of these events has changed over time. Students will investigate the effects of meteor impact events from the past on Earth and other solar system bodies, including the history-altering Chicxulub event, which was most likely the primary cause of the extinction of the dinosaurs and about 75% of life on Earth at the end of the Cretaceous period. Finally, they will use their ideas to analyze the evidence that supports a theory about the formation of the Moon.

The Chelyabinsk anchoring phenomenon was chosen from a group of phenomena aligned with the target performance expectations based on the results of a survey administered to almost 1,000 students from across the country and in consultation with external advisory panels that include teachers, subject matter experts, and state science administrators. The full physics course is designed to purposefully highlight a variety of different types of phenomena. While we design to privilege the interests of students to whom we owe an educational debt, we must not essentialize minoritized groups by assuming that a trend in the data equates to homogenous interests and experiences. Providing a diverse suite of entry points into content and practices creates more opportunities for every student to connect with the content.

The Chelyabinsk phenomenon was chosen for the following reasons:

• Students showed high interest in explaining fireballs and related phenomena.
• Teachers and administrators saw the phenomenon as interesting and on grade band.
• Explaining the mechanics of meteors using physics concepts grounds abstract ideas about orbital motion, gravity, and energy.
• Explaining the phenomenon addresses all the DCIs in the bundle at a high school level.
• Explaining the phenomenon requires the use of mathematical thinking at a high school level.

This unit is the fourth in the OpenSciEd High School Physics course sequence. It is designed to build on student ideas about energy from the first and second units of the course and about forces from the second and third units of the course. In the first unit of OpenSciEd HS Physics, students developed ideas around energy transfer and conservation in the context of charged particles (electrons) colliding with other electrons (electricity) to transfer energy across great distances. In the second unit of the course, earth science phenomena that transfer energy differently across scales of time and space motivated the need for forces to explain our observations. In the third unit, students developed a more robust understanding of forces as vectors and used conservation of momentum to make predictions about the outcomes of collisions. In this fourth unit, students expand their model of forces to include forces of gravity at great distances, using ideas about fields developed in the first unit to understand the relationships between gravity and energy transfer.

In the unit that follows this one, students use energy transfer, electromagnetism, wave mechanics, and forces at a distance to explain how food heats up in a microwave and if or how this technology might be dangerous for humans. In the final unit of the course, students explore cosmology and the Big Bang, applying ideas about forces and energy from all five previous units on the largest scales.

The unit is organized into two main lesson sets. In Lesson Set 1 (Lessons 1-7) students investigate how gravity between two objects changes over distance. They mathematically model gravitational forces at far distances by investigating magnetic forces at tangible distances. They then investigate how forces and tangential velocity can cause objects to move in circles and how this describes how gravity keeps objects in orbit instead of crashing into Earth or the Sun. They derive the relationship between orbital period and radius (Kepler’s third law) through combining the mathematical models for gravity and circular motion, and they reason that meteors like the one they observed during the anchor are not likely to move in circular orbits. Next, they investigate noncircular orbits and learn that all orbits are elliptical (Kepler’s first law), with variation in eccentricity. They reason that this variation of orbit shape can cause orbit paths to cross, creating a potential risk of collision between objects. They model the energy transfer that occurs between the Sun, an orbiting object, and the gravitational field between them to conceptualize the changes in velocity of an object in an eccentric orbit (Kepler’s second law). They use this to consider how we can model the potential for an object to collide with Earth. Finally, they consider the limitation of Kepler’s laws to two-body systems and explore how contact and noncontact forces can change the orbital path of space objects. Students end the lesson set wondering how these concepts of gravity and interactions with nearby objects have and will affect Earth. At the end of this lesson set, students use their ideas to explain how a kinetic impactor and a gravity tractor, two asteroid-deflection strategies, work.

In Lesson Set 2 (Lessons 8-15) students consider Earth’s history and future. They start by analyzing data about objects that recently came close to colliding with Earth and use this to predict the probability of a high-energy collision event. They return to the DQB to evaluate the questions they have answered and brainstorm additional questions based on these data. To answer these new questions, students carry out an investigation to explain which meteor property, its mass or velocity upon impact, can have a larger effect on the amount of damage it can cause. They analyze data on how small objects burn up in Earth’s atmosphere, preventing them from hitting Earth’s surface. They analyze evidence of cratering activity on solar system objects that do not have atmospheres and identify patterns that suggest changes in the frequency of small and large meteors hitting the Earth-Moon system over time. They also analyze evidence of cratering activity on Earth and explore geological processes that help explain the lack of large craters on Earth. They read about an especially large crater in Chicxulub that dates to the same time that there was a mass extinction event on Earth and use these ideas to explain how the impactor led to both short-term and longer-term effects that caused the extinction of only some types of organisms and not others. Finally, they return to the DQB to evaluate the questions they have answered and complete a transfer task on the formation of the Moon.

The following are example options to shorten or condense parts of the unit without eliminating important sensemaking:

• Lesson 3: Students can use the Circular Motion Investigation to collect qualitative data instead of taking actual measurements of the period of revolution using the physical model. This approach allows students to understand the relationship between force and velocity while saving time.
• Lessons 8 and 9: You can condense these lessons into a single lesson and use it as a re-anchor to motivate the lessons in the second lesson set.
• Lessons 12-15: These lessons primarily address Earth and Space performance expectations. If these are not a priority for your school or district, you can conclude the unit after completing Lesson 8. However, students will miss the opportunity to consider the probability of future and past impacts of space objects with our planet.

To extend or enhance the unit, consider the following:

• Lesson 1: Invite students to consider objects they have seen falling from the sky, either from personal experience or from videos. As the unit progresses, ask them to make inferences about these objects, such as their mass or velocity, to help explain the damage or lack thereof upon impact with Earth’s surface.
• Lesson 7: Consider asking students to use a momentum-change perspective to explain how the kinetic impactor strategy works. This will allow you to assess the DCI PS2.A: Forces and Motion.
• Lesson 15: As an end-of-unit project, consider having students design solutions to protect a community or our planet from a collision with a space object.
• All lessons: Remove scaffolds provided with Science and Engineering Practices (SEPs) as a way to give students more independent work with the elements of these practices.

• Diego Rojas-Perilla, Revision Unit Lead, BSCS Science Learning
• Michael Novak, Field Test Unit Co-Lead, Northwestern University
• Laura Zeller, Field Test Unit Co-Lead, BSCS Science Learning
• Zoë Buck Bracey, Coherence Reviewer and Writer, BSCS Science Learning
• Kathryn Fleegal, Writer, Denver Public Schools
• Althea Hoard, Writer, Relay GSE
• Whitney Mills, Writer, BSCS Science Learning
• Madelyn Percy, Writer, Denver Public Schools
• Ann Rivet, Advisor on ESS Integration, Teachers College, Columbia University
• Christopher Soldat, Writer, Van Allen Science Teaching Center
• Alexis Vargas, Writer, Anaheim Union High School District
• Dan Voss, Writer, Northwestern University
• Rabi Whitaker, Writer, New York City Department of Education

• Madison Hammer, Production Manager, University of Colorado Boulder
• Erin Howe, Project Manager, University of Colorado Boulder
• Stacey Luce, Copy Editor, BSCS Science Learning
• Tyler Morris-Rains, Production Support, BSCS Science Learning

An integral component of OpenSciEd’s development process is external validation of alignment to the Next Generation Science Standards by NextGenScience’s Science Peer Review Panel using the EQuIP Rubric for Science. We are proud that this unit has been identified as a quality example of a science unit. You can find additional information about the EQuIP rubric and the peer review process at the nextgenscience.org website.