## Saturday, February 23, 2019

### CAST Reference Sheet: The Good, the Meh, the Bad, and the Wha?

With the NGSS-based California Science Test (CAST) set for its maiden administration this spring, a reference sheet has been prepared. Students have access to the reference sheet while they take the exam. Here's the reference sheet.

CAST High School Reference Sheet

Reference sheet development can awaken passions that physics instructors didn't know they harbored. So let's go through it. (It might be helpful to print the sheet or have it open on another screen. Blood pressure medication? A preemptive dose might save a life here.)

FORCES AND ENERGY
Good: Newton's Second Law, the weight equation, universal gravitation, Coulomb's law, gravitational potential energy, kinetic energy, work-energy theorem. All good.

Meh: Using w for weight. A little bit non-standard, but the judges will allow it.

MOTION
Good: Ft = mv, the use of ∆v in the equation for acceleration: the ∆ is critical here.

Meh: The use of ∆t rather than t. We never create problems involving isolated clock readings (t); intervals (∆t) are always given. The ∆ in front of the x in the equation for speed? I can take it or leave it.

Meh: The use of J for momentum. That's a rare one. I've seen it, but it is not common. I prefer ∆p, and I don't think I'm alone.

Bad: s for speed. I am reminded of a line from Star Trek: "A Vulcan would not cry out so." In this case, I will turn that phrase to "A physics teacher would never, ever use s to denote speed. Ever." I hope I'm not being ambiguous here. The very use of s for speed makes me wonder if anyone associated with physics instruction was involved in developing this reference sheet. A math teacher might make such a miscue, but not a physics teacher.

Wha?: Using the Greek letter, rho (ρ), for momentum. Why? Lowercase ρ is a symbol used to represent density in high school or college courses. It is also used to represent resistivity. Nobody ever uses ρ to represent momentum. Anywhere, ever! Momentum is represented with the letter p. Extra effort is required to insert the letter ρ. I am dumbfounded.

KEPLER'S LAWS
These are here for the benefit of items addressing Earth Science PE, HS-ESS1-4. I'll let them "Meh" or "Wha?" the notion that e = f/d is among Kepler's Laws.

WAVES
Good: The wave equation and the Planck-Einstein relation. I would have put them in that order, but okay.

Wha?: The reference sheet is set in a sans serif font. In high school, we use lowercase f for frequency. Someone at CAASPP seems to have found the special character, ƒ, which bears a striking resemblance to an italicized, lowercase f. If a pianist sees two of those in a row (ƒƒ), they'll hit the keys hard. The symbol, itself, is called "F with hook," or "florin symbol" and is used to denote the Dutch guilder, for example. This has been Sheldon Cooper's "Fun with Fonts" with your host, Sheldon Cooper.

EXPERIMENTAL DESIGN
Mostly good. It it's me, I'd use a cross (×) rather than a bullet (•) to indicate multiplication. The bullet really isn't a multiplication symbol. The dot (·) is, but the cross is more appropriate here.

At the risk of belaboring a point made in the post critiquing the practice items, I will point out to our gentle readers that no reference to index of refraction appears on the reference sheet. No n = c/v and (thankfully) no Snell's law. Recall that one of the practice items expected students to be familiar with the meaning of index of refraction.

CONSTANTS
If someone at CAASPP sees this, please explore the use of the dot symbol ·. On my Mac, I hold down  the shift and option keys while typing a 9. It's more professional than the big bullet • that you get with option+8. And drop the spaces in unit configurations.

I see N·m as better than N • m for newton-meters.

In all, the reference sheet is more good than meh, bad, or wha? But I wouldn't be keen to print it up and have students use it throughout the year. Replace the speed s with a v and the momentum rho with a p, and I can live with the remaining quirks.

## Thursday, February 21, 2019

### CAST Practice—An Analysis of the Physics Questions

The California Department of Education's California Assessment of Student Performance and Progress program has released a set of High School Practice Items in connection to the state-mandated exams to be administered this spring.

As detailed in a previous post, six of the 50 released items relate to high school physics topics. Sixteen are from Life Science, 15 from Earth Science, 9 from chemistry, and 4 from Engineering Design.

Remember: chemistry and physics topics have been combined into the more omnibus "Physical Science" realm of the high school science Performance Expectations (PEs). While NGSS's HS-PS1: Matter and Its Interactions is predominantly chemistry, HS-PS2 Motion and Stability: Forces and Interactions, HS-PS3 Energy, and HS-PS4 Waves and Their Applications in Technologies for Information Transfer are predominantly physics PEs.

Nevertheless, 9 of the 15 released HS-PS items assessed HS-PS1 while 6 were shared among PS2, PS3, and PS4. If there is a blueprint available for the composition of the operational exam, I am not aware of it. So the Practice Items may or may not reflect the mix of the operational exams.

UPDATE: I found the blueprint: for the high school test, see page 8 of the CAST Blueprint. Not surprisingly, it appears the operational exam will include physics items in greater proportion than in the released practice items.

Let's take a look at those six. I will state each item's Item-Level Claim Statement (ILCS). Click the ILCS to see the actual item. My analysis will follow each ILCS.

Identify the relationship between mass and acceleration. [Click to see item.]
In general, the item is perfectly reasonable. It speaks to the interpretation of graphed data obtained through a laboratory activity that might be done in a high school setting. The item links solidly with the corresponding PE (HS-PS2-1: Analyze data to support the claim that Newton’s second law of motion describes the mathematical relationship among the net force on a macroscopic object, its mass, and its acceleration.).

But there is a problem. And I say this as someone who had the privilege of sifting through many, many potential exam items offered by ETS for use in state-mandated testing from 2003 to 2013. The problem is the title of the graph.

Classroom teachers come across as dictatorial joy-crushers when they make any attempt to direct their students to conform to established conventions. Titling a graph is but one such challenge. The title of a scientific graph is Dependent Variable vs. Independent Variable.

The graph on this item is correctly constructed as Acceleration vs. Mass: experimenters would have measured the acceleration of a cart while varying the cart's mass. But the graph is titled Mass vs. Acceleration. I have to assume this was an oversight on the part of ETS and anyone (if there was anyone) tasked with content review.

Mathematically determine the properties of the system using the conservation of momentum of objects in the system.
A fair enough item to assess the corresponding PE (HS-PS2.2: Use mathematical representations to support the claim that the total momentum of a system of objects is conserved when there is no net force on the system.).

Some might object that the mathematics is simplified too much in this item. It does leave open the question of how deep the arithmetic might go in operational items. If you make this question about a neutron and a deuteron combining to form a triton, the principle is same, but the numbers are more formidable.

In the event that anyone tries to champion the new assessments as ground-breakingly novel, consider this released test question from the old Academic Content Standards era: Conservation of Momentum RTQ. In fairness, the new one does have color. And kilograms, rather than tons!

But this brings up an ongoing problem suffered by standards exam item-writers. Standards (now PEs) are often important-sounding principles that turn out to be difficult to write a variety of items for.

Select the design solution that best meets the provided criteria about momentum and force during a collision.
This item reveals the challenges associated with writing questions for PEs like HS-PS2-3: Apply scientific and engineering ideas to design, evaluate, and refine a device that minimizes the force on a macroscopic object during a collision. The item has a very long stem leading to the answer choices. And the choices are quite word-heavy, too.

Students with a firm grasp of the fact that increasing impact time reduces impact force will find their way to the correct answer. The item will make them work for it, though. I'm not faulting anyone here: awkwardness is in the nature of writing items aligned to standards (PEs) like this.

Create a correct mathematical representation to determine the components of gravitational potential energy in the Earth-ball system and kinetic energy.
This one requires a written response and is graded with a rubric.

It is linked to 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.

Might it connect more directly to 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 motions of particles (objects) and energy associated with the relative position of particles (objects)? The clarifications on PS3-2 say "Examples of phenomena ... could include the conversion of kinetic energy to ... energy stored due to position of an object above the earth. Examples of models could include diagrams, drawings, descriptions, ...]

Aligning items to PEs is sometimes a dark art; I'm inclined to grant CAASPP latitude on this matter.

I have reason to suspect Rhett Allain will not approve of dropping a tennis ball from the top of a building and stating that air resistance is negligible. Neglecting air resistance is a simplifying step. Dropping a tennis ball might be a requirement of item-writing guidelines that prohibit scenarios that might cause significant injury. Dropping a cannon ball would inherently render air resistance more negligible, but would also present a greater potential (!) for damage if carried out in real life.

There's some contrivance at work here: Determining the kinetic energy of a dropped ball in reality would involve measuring its mass and its speed. The speed, alone, allows one to determine the height from which the ball was dropped. But the standard demands items, so here we are.

Describe how wavelength is related to the change in the medium.
The PE being addressed here is HS-PS4-1: Use mathematical representations to support a claim regarding relationships among the frequency, wavelength, and speed of waves traveling in various media. The Disciplinary Core Idea expands this to: The wavelength and frequency of a wave are related to one another by the speed of travel of the wave, which depends on the type of wave and the medium through which it is passing.

One word that doesn't appear anywhere in the HS-PS PEs is "refraction". So we have a judgment call here. Do we assess attainment of this PE by asking about what does or doesn't change at an optical boundary during the process of refraction?

Students must also know what index of refraction refers to and that greater values indicate slower transmission speed in transparent materials. I'm delighted to teach the material; no one gets through my course not knowing how rainbows work. But I might have omitted index of refraction thinking no harm would come to my students based on a strict reading of the PEs and DCIs. I would have been wrong.

There are certainly topics I am skipping based on my reading of NGSS. Which ones will show up in the assessments? Time will tell. I'm not a huge fan of surprises like this.

Minor point: Numerical values were used for the indices of refraction and for the wavelength of the laser. I'm not sure why an infrared wavelength was chosen. When I use lasers in class, I prefer to stick to visible light varieties.

Quantify the change in energy associated with the appropriate change in the relative orientation of the two objects.
The item is a pretty spot-on assessment of the PE here, HS-PS3-5: Develop and use a model of two objects interacting through electric or magnetic fields to illustrate the forces between objects and the changes in energy of the objects due to the interaction.

I like this one because it shows a weakness in my own instruction that will require a bit of patching up.

During classroom instruction, students should be able to examine a number of systems and understand how potential energy changes within them. A rock and the Earth, two opposite charges, two like charges, magnets, springs... Students should know where potential energy is zero and where it is maximized in a given system.

I'll need to work on more explicit instruction of that beyond gravitational systems.

If you made it all the way to the end, pat yourself on the back. This was a long one. I will nourish a hope that we get more released items each year. I was unambiguous about this priority when I served on California's Assessment Review Panel. But panelist's wishes were not always accommodated. I really am trying to be subtle here! In any case, I will try to maintain cautious optimism.

Having said that, I will add that the most fun I had practicing and honing the craft of teaching physics occurred in the years when my students were not assessed with end-of-course exams intended to enforce a measure of accountability. My students in that era did not leave my course with woeful gaps in their physics knowledge. But that's just me shaking my fist at the sky.

## Monday, February 18, 2019

### Roadmap to the End of Physics

I believe the first time Physics was offered at Rio Americano High School, it was for the 1966-67 school year. My now-retired former colleague, Marion Gribskov taught the course for 19 years until he was called upon to teach Chemistry in 1985-86. I began teaching Physics in 1986. Based on my current reading of the tea leaves, I will teach Rio's final Physics classes in 2020-21.

In 2021-22, I will begin teaching Physics of the Universe (PotU). This will be our school's adaptation to the Next Generation Science Standards and the California Science Framework's digestion of NGSS.

As with most transitions of magnitude, there will be some awkwardness. I have penciled out a roadmap that will take my school from where we are now to where we need to be in 2023.

Here are the accompanying notes, for what they're worth.

PotU/11-12: Physics of the Universe for Juniors and Seniors. “Algebra 1”-equivalent prerequisite. These juniors and seniors will have had the opportunity to enroll in Biology of the Living Earth and Chemistry in the Earth as freshmen and sophomores.

PotU/11-12 might be a transitional course for use during Rio’s migration to the NGSS Three-Course model. It will be taught in 2021-22 and 2022-23 only. For 2023-24 and beyond, PotU will be a 9-10-level course. PotU/11-12 might be retained to accommodate juniors and seniors who did not enroll in PotU/9-10 but aren’t up to the challenge of AP Physics 1.

PotU/11-12 will omit physics topics not included in the California Framework Physics of the Universe course model, and add earth science topics as needed.

PotU/9-10: Physics of the Universe for Freshmen and Sophomores can omit the math prerequisite but will need to integrate some elements of algebra instruction.

Concurrent offerings of PotU/11-12 and PotU/9-10 in 2021-22 and 2022-23 are to prevent classrooms populated with freshmen through seniors. We put an end to this practice with Earth Science in 2016 with the introduction of Conceptual Physics. Earth Science was restricted to freshmen and sophomores while Conceptual Physics was restricted to juniors and seniors..

Development of Rio’s Physics of the Universe courses will be undertaken during all available collaboration time in 2019-20 and 2020-21 and additional time as needed and approved.

*Beginning in 2022-23, the prerequisite for AP Physics 2 will be “successful completion of AP Physics 1.” [The previous prerequisite had been “successful completion of Physics or AP Physics 1.”]

**Beginning in 2023-24, PotU/11-12 will be discontinued and PotU/9-10 will be the sole non-AP Physics course.

It should be noted that my district has not adopted physics textbooks since 2008. While the district has opted for the three-course model, it doesn't seem any textbook/curriculum program exists for this new course.

It seems there is an assumption among NGSS visionaries that they have provided a grand vision, and now it's up to classroom instructors to develop the curriculum that will implement their vision. That's simply not going to happen. I'm delighted to develop curriculum... to implement my own vision of what high school physics instruction should be. Anyone else who has a vision needs to provide their corresponding curriculum if the hope for implementation.

Between now and then, things may change in terms of the process. This is version 1.0 of how I think it will all go.

## Sunday, February 17, 2019

### Practice items for California's upcoming NGSS test

The time has come for students of science in California. That's right, CDE's CAASPP's NGSS CAST from ETS goes operational this spring.

That wasn't a cat walking across my keyboard; that was the initialisms and acronyms that spell out the new state-mandated assessment regime in California.

NGSS is, of course, the Next Generation Science Standards. CAASPP is the CAlifornia Assessment of Student Performance and Progress. CAST is CAlifornia Science Test. (I'm suddenly envious of the science tests given in Missouri and Virginia, less so for those in Colorado, Delaware, Georgia, Hawaii, Maine, Nebraska, Rhode Island, Washington, Wisconsin, and lastly, Louisiana. ETA: Looks like I missed Michigan and passed Pennsylvania. I'll be here all weak.)

NGSS has been around for some time now, with its multi-colored documentation of Performance Expectations, Science and Engineering Practices, Disciplinary Core Ideas, and Crosscutting Concepts. California has digested NGSS into its own Science Framework. The Framework and NGSS articulate broad, sweeping visions of science instruction.

CAASPP is the program tasked with testing. The previous iteration of this (in California) was State Testing And Reporting (STAR). This is where the lofty visions presented in the vision documents (NGSS/Framework this time) must be broken down into test questions ("assessment items"). As it was during the STAR era, the California Department of Education (CDE) has contracted the services of Educational Testing Services (ETS) to develop the CAST. (The proliferation of initialisms and acronyms indicate the importance of the enterprise.)

Assessments are where the rubber of the grand visions meet the road of perceived accountability. I say this as someone who served on the Golden State Exam development committee and was appointed by the State Board of Education to serve on CDE's CRP (Content Review Panel, later rebranded as the ARP: Assessment Review Panel).

I am a relentless advocate for released test questions (RTQs). The vision documents are necessary, I suppose. But they never really specify measurable outcomes. The visions boil down to "all students should be knowledgeable in science and capable of performing scientific analysis and related tasks." But vision documents quickly blow up into phonebook sized documents with webs of interrelated objectives that can make tri-level chess seem simple by comparison. But with a sufficient bank of RTQs, I will know exactly what your vision was. Inductive reasoning is really the only way to connect standards and assessments, here.

Until recently, there were just a handful of CAST RTQs available. You can find them on the California Science Test Training Items Scoring Guide: High School (PDF).  The mix of topics (PE/DCIs) left much to be desired.

Life Science: 6 - Earth Science: 1 - Physical Science: 0 - Engineering Design: 0

Remember that in NGSS, high school science opposes three domains: Life Science, Earth Science, and Physical Science. The old subjects known as "chemistry" and "physics" have been combined into Physical Science. But not even one RTQ covered anything in Physical Science.

More recently, a raft of 50 RTQs has been launched. You can find them on the California Science Test Practice Items Scoring Guide: High School (PDF). The mix seems a bit better:

Life Science: 16 - Earth Science: 15 - Physical Science: 15 - Engineering Design: 4

Of the 14 items tagged as Physical Science, 6 related to topics covered in physics. The other 9 were chemistry questions.

Comments and criticism of specific items will be offered in a later post.

## Saturday, February 16, 2019

### The Lessons of Phyz — 2019

The Lessons of Phyz store at Teachers Pay Teachers is now one year old and features even more items than it did last time I posted about it. I know, right? It began with question sets for the classic, Mechanical Universe: High School Adaptation—a video series that you can neither buy nor stream in 2019. Since then, I've added video question sets to more than cover your next jury duty needs. Here are all the delicious digital documents on offer as of February, 2019.

Cosmos: A Personal Journey by Carl Sagan [1980]. Question sets for all 13 episodes: The Shores of the Cosmic Ocean, One Voice in the Cosmic Fugue, Harmony of the Worlds, Heaven and Hell, Blues for a Red Planet, Travellers' Tales, The Backbone of Night, Journeys in Space and Time, The Lives of the Stars, The Edge of Forever, The Persistence of Memory, Encyclopaedia Galactica, Who Speaks for Earth?

Cosmos: A Spacetime Odyssey hosted by Neil deGrasse Tyson [2014]. Question sets for all 13 episodes: Standing Up in the Milky Way, Some of the Things That Molecules Do, When Knowledge Conquered Fear, A Sky Full of Ghosts, Hiding in the Light, Deeper Deeper Deeper Still, The Clean Room, Sisters of the Sun, Hidden Worlds of Planet Earth, The Electric Boy, The Immortals, The World Set Free, Unafriad of the Dark.

How Earth Made Us | How the Earth Changed History by Professor Iain Stewart. Question sets for all five episodes: Deep Earth | Beneath the Crust, Water | Water World, Wind | The Skies Above, Fire | The Gift of Fire, Human Planet | The Human Era.

Physics: Electricity and Magnetism. Question sets for documentary program episodes, Lightning!, Search for the Super Battery, Magnetic Storm, Aurora - Fire in the Sky.

Physics: Modern Physics. Question sets for feature-length documentary films, Einstein's Big Idea and Atomic Café.

The Singles Series
Single-item question sets. Some are included in modules elsewhere in The Lessons of Phyz.
Merchants of Doubt
Before the Flood
Secrets of the Psychics

The Mechanical Universe: High School Adaptation
Mechanical Universe 1: Motion and Forces
The Law of Falling Bodies, The Law of Inertia, Newton’s Laws, Moving in Circles

Mechanical Universe 2: Gravity
Kepler’s Laws, The Apple and The Moon, Navigating in Space, Curved Space and Black Holes

Mechanical Universe 3: Conservation
Conservation of Energy, Conservation of Momentum, Angular Momentum

Mechanical Universe 4: Temperature, Vibrations, and Waves
Temperature and the Gas Laws, Harmonic Motion, Introduction to Waves

Mechanical Universe 5: Electrostatics
Electric Fields and Forces, Equipotentials and Fields, Potential Difference and Capacitance, The Millikan Experiment

Mechanical Universe 6: Circuits And Magnetism
Simple DC Circuits, Magnetic Fields, Electromagnetic Induction, Alternating Current

Mechanical Universe 7: Light And The Atom
Wave Nature of Light, Models of the Atom, Wave-Particle Duality

The Earth Science Series
Earth Science 1: Science, Mapping, and Water
Secret of the Psychics, Lost at Sea: The Search for Longitude, Water, Earth Under Water

Earth Science 2: Atmosphere and Weather
Our Atmosphere, Predicting Weather, Wind

Earth Science 3: Climate Change and Human Impact
Megastorm Aftermath, Before the Flood, Human Planet

Earth Science 4: Tectonics, Volcanoes, and Earthquakes

Earth Science 5: Astronomy in the Solar System
Meteor Strike, Life Beyond Earth: 1. Are We Alone?, 2. Moons & Beyond, Secrets of the Sun

Earth Science 6: Astronomy Beyond the Solar System
Life & Death of a Star, Invisible Universe Revealed, Alien Planets Revealed, Alien Galaxies

Question sets covering Paul Hewitt's Conceptual Physics Alive! video series are available from Arbor Scientific in two ways: The Complete Edition (hard copies and PDFs on DVD) and Disk Edition (PDFs on DVD).

## Monday, February 11, 2019

### The Inverse Leidenfrost Effect at Veritasium

Here at The Blog of Phyz, we're big fans of the Leidenfrost effect. If you search "Leidenfrost" here, you'll see exactly how much we love it. I blame Jearl Walker.

As always, Veritasium's Derek Muller gets us.

Inverse Leidenfrost? What can that possibly be about? Take a look:

The Inverse Leidenfrost Effect

## Sunday, February 10, 2019

### Physics Fun on Localish

Ray Hall is a California physics professor and a skeptic friend from way back. So yes, he is made of win.

He has also crafted arguably the best account on Instagram: physicsfun. And by "arguably" I mean that you and I might have an argument if you think there's a better Instagram account out there.

As a delightful bonus, physicsfun passed the million follower mark months ago: a reason to be hopeful for the future.

If you don't have an account on Instagram, physicsfun is a reason to get one.

Folks are taking note. ABC's Localish produced a nice segment on Ray and his Instagram.

S1E31 Crazy for Physics on Instagram

Instagram: physicsfun

## Saturday, February 09, 2019

### It's scientist valentines time!

The album is here. The movie is here. And the printable is here. Enjoy!

## Wednesday, February 06, 2019

### Which way is north? Not so fast...

It isn't where we left it.

Over the course of geologic time, magnetic north wanders like the oft-maligned "drunken sailor". And it reverses polarity on a not-entirely-stochastic basis. It seems the pole is on the move again—with faster than normal speed—and models will need to be updated to keep pace.

As Magnetic North Pole Zooms Toward Siberia, Scientists Update World Magnetic Model

The North Magnetic Pole Is Shifting East, Fast

Even in the era of GPS, Earth's magnetic field is still an important component in terrestrial navigation.

## Sunday, February 03, 2019

### Torque-Master Challenge 2019

After completing the "Torque Feeler" / "It's All in the Wrist" Conceptual Physics Lab Manual activity, we add the Torque-Master Challenge.

We again repurpose our five-foot aluminum tube from the Pasco Scientific Lenz's Law Demonstration set. Sometimes we use it as a blow gun. Sometimes we use it for examples of resonance. This time, we tie an ordinary 500-mL water bottle to the end. Challengers must hold the arrangement level for ten seconds.

Over the years, I have found that very few of my students can do this. I can, and I am not young, cut, ripped, or chiseled. And I do not lift. I mean, look at me in the video. Honestly!

Torque-Master Challenge 2019

Why I can do this while so few of my students can is a mystery I have no answer to. Now that I think of it, though, very few of them can match my speed when we use this tube as a blow gun. I have no explanation.

When we find students cannot match my blow gun speed, I admonish all of them to quit smoking!