January/February 2018 – Vol. 31 No. 2

## The Teaching Length Scale

Posted: Tuesday, May 6th, 2014

by Galen T. Pickett

Physics can be organized by the size and duration of events. When we teach Newton’s mechanics, the examples we use typically are on length scales of meters and on time scales of seconds (tossing a ball, sliding into second base) and run up to solar system scales (tens of millions of kilometers for an Astronomical Unit, and tens of millions of seconds for a year). But, unless your classroom is equipped with technology at the extreme ends of the sophistication scale (chalkboards at the primitive end, and SmartBoards at the super-fancy end), you probably use ordinary whiteboards and erasable marker to make sketches and calculations for your students. The marks you make on this surface meet some basic criteria: they have to be wide enough (half a centimeter or so) to be clearly seen from every vantage in your room and they have to strongly absorb visible light – making a visibly saturated mark. The width of the marks is controlled by the properties of the pen tip, and the saturation of the marks is controlled by the pigment in the marker, but there is another, often overlooked length scale in your markings.

What is the thickness of the marks? It can’t be zero, and it can’t be on the order of millimeters (you can easily feel roughness on the scale of tenths of millimeters with your fingertips, the width of a single human hair). What I have below can be organized into a demonstration or a full experiment supporting topics in waves and optics.

• Have a supply of “wet” whiteboard markers on hand. A couple of different colors if you are doing a demonstration, enough for each group to have one if this is a class-wide exploration.
• Make several marks (or have your kids make marks on their whiteboard slabs), different orientations, curly-cues, some nice cursive if you can manage it, ask for what length scales your students observe.
• Ask about the thickness of the marks … how far from the surface of the whiteboard do they jut?
• Use a web-camera and a second light source to show what the marks look like up-close. Make sure you can see the marks “through” the reflection of your light source.
• If you see other colors … and you will … ask your students if that reminds them of anything. Rainbows, and soap-bubbles, oily sheen are what comes to my mind.
• What happens when marks “cross” each other? If you press hard when writing, where do you expect the marks to be thinnest?

Figure 1

Here is what is happening. The “green” and “yellow” rays add up “constructively.” (See Figure 1.) That is, they are in constructive interference so you see this wavelength strongly reflected, even if this color were not present in the pigments of the oily marker layer.

The presence of this “rainbow” (see Figures 2 and 3) indicates that there is some interference going on, so the thickness of the marker layer has to be comparable to the wavelength of visible light.

Green light is in the neighborhood of 500 nanometers in wavelength, or 0.5 micrometer. A human red blood cell is approximately a disk of thickness 5 micron, and radius 15 micron, so the marks you use to teach physics are a factor of ten smaller than that cellular scale. When you teach physics, astrophysics, mathematics, history and poetry, you are using one of the great sub-micron teaching technologies of the twentieth century.

Dr. Galen T. Pickett is with the Department of Physics and Astronomy at CSU Long Beach and a member of CSTA.

#### Written by Guest Contributor

From time to time CSTA receives contributions from guest contributors. The opinions and views expressed by these contributors are not necessarily those of CSTA. By publishing these articles CSTA does not make any endorsements or statements of support of the author or their contribution, either explicit or implicit. All links to outside sources are subject to CSTA’s Disclaimer Policy: http://www.classroomscience.org/disclaimer.

# LATEST POST

## Accelerating into NGSS – A Statewide Rollout Series Now Accepting Registrations

Posted: Friday, January 19th, 2018

Are you feeling behind on the implementation of NGSS? Then Accelerating into NGSS – the Statewide Rollout event – is right for you!

WHO SHOULD ATTEND
If you have not experienced Phases 1-4 of the Statewide Rollout, or are feeling behind with the implementation of NGSS, the Accelerating Into NGSS Statewide Rollout will provide you with the greatest hits from Phases 1-4!

OVERVIEW
Accelerating Into NGSS Statewide Rollout is a two-day training geared toward grade K-12 academic coaches, administrators, curriculum leads, and teacher leaders. Check-in for the two-day rollout begins at 7:30 a.m., followed by a continental breakfast. Sessions run from 8:00 a.m. to 4:15 p.m. on Day One and from 8:00 a.m. to 3:30 p.m. on Day Two.

Cost of training is \$250 per attendee. Fee includes all materials, continental breakfast, and lunch on both days. It is recommended that districts send teams of four to six, which include at least one administrator. Payment can be made by check or credit card. If paying by check, registration is NOT complete until payment has been received. All payments must be received prior to the Rollout location date you are attending. Paying by credit card secures your seat at time of registration. No purchase orders accepted. No participant cancellation refunds.

REGISTER

http://bit.ly/ACCELERATINGINTONGSS

DATES & LOCATIONS
MARCH 28-29, 2018
Host: San Mateo County Office of Education
Location: San Mateo County Office of Education, Redwood City

APRIL 10-11, 2018
Host: Orange County Office of Education
Location: Brandman University, Irvine

MAY 1-2, 2018
Host: Tulare County Office of Education
Location: Tulare County Office of Education, Visalia

MAY 3-4, 2018
Host: San Bernardino Superintendent of Schools
Location: West End Educational Service Center, Rancho Cucamonga

MAY 7-8, 2018
Host: Sacramento County Office of Education
Location: Sacramento County Office of Education Conference Center and David P. Meaney Education Center, Mather

JUNE 14-15, 2018
Host: Imperial County Office of Education
Location: Imperial Valley College, Imperial

Presented by the California Department of Education, California County Superintendents Educational Services Association/County Offices of Education, K-12 Alliance @WestEd, California Science Project, and the California Science Teachers Association.

#### Written by California Science Teachers Association

CSTA represents science educators statewide—in every science discipline at every grade level, Kindergarten through University.

## The Teaching and Learning Collaborative, Reflections from an Administrator

Posted: Friday, January 19th, 2018

by Kelly Patchen

My name is Mrs. Kelly Patchen, and I am proud to be an elementary assistant principal working in the Tracy Unified School District (TUSD) at Louis Bohn and McKinley Elementary Schools. Each of the schools I support are Title I K-5 schools with about 450 students, a diverse student population, a high percentage of English Language Learners, and students living in poverty. We’re also lucky to be part of the CA NGSS K-8 Early Implementation Initiative with the K-12 Alliance. Learn More…

#### Written by NGSS Early Implementer

In 2015 CSTA began to publish a series of articles written by teachers participating in the California NGSS k-8 Early Implementation Initiative. This article was written by an educator(s) participating in the initiative. CSTA thanks them for their contributions and for sharing their experience with the science teaching community.

## 2018 CSTA Conference Call for Proposals

Posted: Wednesday, January 17th, 2018

CSTA is pleased to announce that we are now accepting proposals for 90-minute workshops and three- and six-hour short courses for the 2018 California Science Education Conference. Workshops and short courses make up the bulk of the content and professional learning opportunities available at the conference. In recognition of their contribution, members who present a workshop or short course receive 50% off of their registration fees. Click for more information regarding proposals, or submit one today by following the links below.

Short Course Proposal

#### Written by California Science Teachers Association

CSTA represents science educators statewide—in every science discipline at every grade level, Kindergarten through University.

Posted: Monday, January 15th, 2018

by Holly Steele

The California Science Teachers Association’s mission is to promote high-quality science education, and one of the best practice’s we use to fulfill that mission is through the use of our Facebook group pages. CSTA hosts several closed and moderated Facebook group pages for specific grade levels, (Elementary, Middle, and High School), pages for district coaches and science education faculty, and the official CSTA Facebook page. These pages serve as an online resource for teachers and coaches to exchange teaching methods, materials, staying update on science events in California and asking questions. CSTA is happy to announce the creation of a 6th group page called, California Administrators Supporting Science. Learn More…

#### Written by Guest Contributor

From time to time CSTA receives contributions from guest contributors. The opinions and views expressed by these contributors are not necessarily those of CSTA. By publishing these articles CSTA does not make any endorsements or statements of support of the author or their contribution, either explicit or implicit. All links to outside sources are subject to CSTA’s Disclaimer Policy: http://www.classroomscience.org/disclaimer.

## Find Your Reason to Engage

Posted: Monday, January 15th, 2018

by Jill Grace

I was recently reflecting on events in the news and remembered that several years ago, National Public Radio had a story about a man named Stéphane Hessel, a World War II French resistance fighter, Nazi concentration camp survivor, and contributor to the United Nation’s Universal Declaration of Human Rights. The story focused on a book he had published, Time for Outrage (2010).

In it, Hessel makes the argument that the worst attitude is indifference:

“Who is in charge; who are the decision makers? It’s not always easy to discern. We’re not dealing with a small elite anymore, whose actions we can clearly identify. We are dealing with a vast, interdependent world that is interconnected in unprecedented ways. But there are unbearable things all around us. You have to look for them; search carefully. Open your eyes and you will see. This is what I tell young people: If you spend a little time searching, you will find your reasons to engage. The worst attitude is indifference. ‘There’s nothing I can do; I get by’ – adopting this mindset will deprive you of one of the fundamental qualities of being human: outrage.  Our capacity for protest is indispensable, as is our freedom to engage.”

His words make me take pause when I think of the status of science in the United States. A general “mistrust” of science is increasingly pervasive, as outlined in a New Yorker article from the summer of 2016. Learn More…