This photo was taken near here
Dr. Tom Bensky
Professor of Physics
Cal Poly Physics Department
I like tinkering with teaching and am always looking for new ways of injecting modern ideas and technology into what I do. Here is some of my work.
I coded up an attendance system called Youhere.org that
allows teachers to take attendance by having students "check-in" to class using their
location-aware phones. Check it out!
As you probably know, the Arduino is a
hugely popular microcontroller. A while back, as part of our 'advanced electronics' class
(PHYS 357), I started using the Arduino as the core of a data-logger project. In this
project, students would choose a sensor (from dozens available, like temperature,
pressure, etc.) and interface it to an Arduino. They would then also interface the Arduino to
an SD-Card module, and program it to log readings from their sensor, to the SD-card, for
Construction of the data logger aside, the most creative element of this project
is in allowing the students to decide how and where to deploy the data-logger. I've seen students take it
on hikes, attach it to their cars or bikes, take into exercise classes, and even put it on a horse saddle while riding.
I've come to like this project because taking data in an automated fashion (i.e. no paper,
stopwatches, yardsticks, string, tape, etc.), retrieving the data, plotting the data, then
coming up plausible 'story' to describe the data is to me, the epitome of what a scientist
I have found this project to be remarkably adaptable to a variety of audiences.
Currently, I've done it witg advanced physics majors, high school juniors/seniors, and
freshman Liberal Studies majors.
Here are copies of my core lessons (thank you M.M. for proofreading these). These were run over 4 class sessions, using about four hours of class time,
culminating in a lesson on how to make a proper plot (title axes, etc.) and a presentation to the class on the
results (i.e. the 'story' behind the data).
The culminating event is when each group presents their project to the class. At all levels, I am always pleasantly surprised by the
creative (and sometimes crazy) scenarios students find for their data logger---and most of the time, I don't
know the details until their presentation. (A photo of their data logger "in action" is required in their presentation.)
Prolog and Symbolic Processing with Kinematics Problems
If you look carefully at physics problems in an introductory physics book, they can all be solved algorithmically. That is,
if you simply find or compute quantities, in the right order, using either 1) common sense, or 2) the equations given in the
book, you'll get the correct answer, every time. You just have to find that 'right order.'
This paper I wrote a while back
discusses this in the context of 1D kinematics problems, involving only one moving object. Here
is the code for it, if you want to investigate it further.
3D Printing Gotchas
No matter what brand of 3D printer you buy, it won't always work.
If it bends upward, increase the nozzle temperature in 5 deg C increments.
Build Plate Temperature
Glass at 80C
Build Plate Leveling
A piece of paper between nozzle and printbed should require a moderate amount of tugging to extract. You want that
first layer to be squished and flattened onto the build plate.
Quizable.org: Put deadlined questions in front of your students quickly (note: has a peer-reviewed, up/down-vote homework submission mode).
Quizable cuts down on the number of 'clicks' required to post a question (a la Moodle), by using a 'programmatic' approach
to describing questions.
Introductory Electricity and Magnetism
E&M tends to be a very "mathy" course. Thus, I started to use Sagemath (now CoCalc) in this class to help us
wade through the math. Here are some of my activities using CoCalc.
Use CoCalc to work out math issues that come up in a course like this.
Spreadsheet to compute (lat,long) from deduced reckoning steps.
Electronics (PHYS 206 here)
Most of what I know about electronics was self-taught by reading
everything I could find by Forrest
Mims and building circuits in my garage with stuff I bought at
Radio Shack or here. I find
Mims' hands-on, active and "circuits that do something" approach goes
quite far for both teaching and learning electronics. I think
one of finest introductory books on electronics ever written.
I put together the core of these labs
(C. Hoellwarth and M. Moelter helped a great deal to get these labs in
shape) to cover our 10 week electronics class.
I started running this class in "project/makers" mode in Spring
2011 and continue to do so. Here are
the three projects students are to do over the course of the quarter.
I thank my colleague Matt Moelter for his help in refining this curriculum and jumping in and teaching it with me.
The labs in our department (and dare I say colleges everywhere), tend
to be rather like “cook-books.” We put students in front of a
equipment (a good thing), but then give them step-by-step instructions
like “turn the voltage to 10, then write down the ion current” (a bad
thing). Afterward, we tell the students what their data should look
like, and even (exactly) how to analyze it. We don’t give the students
much room to think on their own. To this end, a nice paper
came out about giving labs where you remove the procedure from a
typical lab, thus letting the students debate and assess what needs to
be done to achieve a particular (measurement) goal given some
So, in the Winter of 2015, I did this for
our optics labs (that is, removed the procedure from the labs). I
kept the labs to just two pages, with no procedure, and a clear
grading rubric for each. Here are my revised labs.
For some of the labs, I let the students take a break from writing
formal lab reports, allowing them to draw “howtoons” of their results
instead. Here’s what I got for the polarimetry lab: click.
Although removing the procedure and allowing the students to think
sounds like a good idea, it wasn’t. The students appear to love being
told exactly what to do (a la the “cookbook” mode), and would spend most
of the lab period desperately searching the web for instructions. One
student even found a cookbook lab at another university and raised his
hand to ask me “can I just do this instead?” Oh well.
Introduction to the Solar System (ASTR 101 here)
I started teaching ASTR101 a couple of years ago. It is a very fun
class to teach (except when the students got mad at me for planning
an exam on the day before Halloween, which prevented them from being
able to “get ready for Halloween”). Here are a few “hands-on”
activities I assigned, in order to get the students out and “looking
up” at the sky.
Using an hour here and hour there during summer 2009-summer 2010, I
converted my old 1992 VW GTI to a 100% electric vehicle. Here was
the first step back in August 2009, taking out the dirty old engine.
I sold the engine to a scrap yard for $13.50. First the DC electric motor came in the mail (WARP Impulse 9),
which I mated to the transmission using a custom adapter kit from ElectroAutomotive (which I would not recommend doing ANY business with).
I then put this assembly back into the car, onto the original motor
mounts. For additional support on the motor side, I hand-crafted some
unistrut bracketing, which among other things for the car, I ordered
from my favorite company, McMaster-Carr. The car is a front wheel drive,
so the motor/tranny go in sideways, and connect to two half-axles which
turn the two front wheels. Electric cars are quite simple in operation.
An electric motor turns the gears in the transmission just like the
original gasoline motor did. Check out this video, where I spun up the
car using just a single 12V battery.
Update Aug 2015
To 2013 or so, I drove the car about 8,000 miles before the lead-acid
batteries gave out. They would charge fully, but then be completely
depleted after driving down the street and back. So the car sat in my
garage for about 2 years or so, until I decided to take the plunge and
buy some Lithium-ion ($$$) batteries. I bought 8-Enerdels, at 14.4 each
(32 cells, with a max voltage of 3.9 volts), so the car is now 125V when
all charged up. Here are some pictures...4 batteries in the front:
And four in the back:
I built a cool battery box too:
My "fuel gauge" is a voltmeter, 125V=full, 90V=empty:
I notice that the pack voltage goes down by 1 Volt per every mile that a
drive, so I have about a 35 mile range, which is perfect for living in a
small town like SLO. The batteries require a BMS (battery management
system), which is basically an on-board computer that watches over the
batteries during the charging and discharging (i.e. driving) process.
The cells must stay between 3.9 and 2.8 Volts to avoid damaging them.
But this require a huge rats-nest of wires, to the tune of 5 signal
wires per battery, hence this mess:
That's the BMS unit in the middle right (with the heat-sink fins). That
black cable in the foreground is connected to the accelerator pedal and
the silvery thing to the left is my potentiometer (or "pot box") that
controls the speed of the car. It all works fine and the car is a joy to
drive. I like being able to monitor all batteries using a laptop
connected to the BMS. The batteries are about 1/2 the weight (45 lbs
each, not 75 like the lead acid) and about 2x the energy density.
Although the experience of building the lead-acid version of the car was
good for learning, I really can't stand those types of batteries. They
are heavy, stinky (due to their battery chemistry), and corroded
everything around them. I would not recommend building a lead-acid
Here’s one of my favorite pics of the car, it being “fueled up” in my
driveway. Note how the suspension is still nicely balanced, versus that
with the lead-acid batteries (below).
So what's this longitude thing all about? For starters, read my paper
about it (see ASTR 324 above) or the book I have been writing (see ASTR
324 above). Like everyone else, I read Sobel's book on "Longitude" back in the early 1990s. I had the
opportunity to teach a class in London during the Summer of 2008, and I
thought a course that examined the science behind the longitude problem
would be a great fit. It was, and I have since turned the class into an
general education class here at Cal Poly (ASTR 324) and taught it again
a few times in London during the summers.
The whole story is just awesome, and has been a big part of my
professional work. I've published two papers on it, a self-published
book, and even got in to amateur horology. As a true
"longitude disciple," I found Sir Cloudisley Shovell's Memorial here, and even posed the way the poor guy
was likely found:
The "longitude problem" sort of works like this. Suppose you were a
ship's navigator in the 1700s. You were far from land and looked
out. This is what you saw in all directions, for two months at a time:
The question is then, "where are you?" The sea is pretty featureless
for landmarks to navigate by. So what do you do? Back in the 1700s,
lives were being lost and ships were being crashed. Did you know an
average galleon back in the day took 10,000 oak trees to build (100 acres of trees)?
Latitude (N/S location) is straightforward to find using the sun at
noon, or (if in the northern hemisphere), Polaris at night.
Longitude (your E/W position), however, was not possible to find
using the sky. Why? Well, in short any configuration of the sky can
be produced by viewing it at a given longitude at a given time. Thus,
your view of the sky is an inseparable mixture your time of day and
your E/W position. If you want to use the sky for longitude,
you'll need some absolute reference to disambiguate the two. So basically yes,
in the mid-to-late 1700s, everyone was sailing half blind.
Sticking to strictly E/W ocean crossings was a popular technique
(that is, sail and keep Polaris at the same height in the sky). You
have to remember that back then there was no electricty, GPS,
gasoline, radar, or even reliable maps. As soon as you lost sight
of land, you may as well be on a different planet. Ships were
powered by the wind and made of wood and tar. One would be
very isolated out there on a ship. Yes, yes, on it goes.
Here is an excerpt from my paper:
By the 1700s it was unfortunate that far-reaching expeditions were at
great risk because there was no practical method of accurately
determining one's navigational longitude. There are records of fateful
expeditions both at land and sea5 due to this “longitude problem.”
Conditions at sea made this problem particularly serious, and many
lives,6 property, and political prowess were lost. The longitude problem
is well covered in both erudite and popular treatments.
It was established that the simultaneous knowledge of one's remote
(or “local”) time and that at a fixed reference point16 would allow
for the determination of the relative longitude. Knowing (or keeping)
the time at the distant reference point (from afar) was the most
problematic issue despite three known methods for doing so. The first
involved using the motion of the Moon, the second involved keeping
time with a portable chronometer, and the third used observations of
the motion of Jupiter's moons. These were all sound solutions17 that
lacked a practical implementation. Harsh conditions at sea where
accurate navigation was the most critical posed the greatest
challenges to a longitude solution. Observing Jupiter's moons at sea
was impractical due to the difficulty in tracking them from a rocking
ship. John Harrison spent a lifetime pursuing the chronometer
approach, while a succession of astronomers employed at the Royal
Greenwich Observatory pursued the lunar approach.
The interested parties were all competing for the substantial
“longitude prize” offered by the British government in 1714. The
chronometer approach eventually won, although the techniques using
the Moon and Jupiter (on land) all became usable by the late 1700s.
The accuracy and ease of use of the marine chronometer caused it to
become the dominant longitude-determining tool until worldwide time
broadcasts in the early 1900s. The solution to finding longitude took
the most convenient leap in the early 1990s, with the availability of
the Global Positioning System (GPS). The longitude problem was an outstanding worldwide problem in the
1700s and was eventually solved using principles from physics and
astronomy. We find it an appropriate topic for a college-level course
for nonscience majors for the following reasons.
A course whose
topics include the longitude problem, celestial navigation, and
timekeeping is an original offering of general interest to students.
The longitude problem provides a framework for discussing a variety
of scientific topics in support of understanding this problem (and
its solution) from a historical and contemporary perspective.
The longitude saga also presents an opportunity to demonstrate how
science has worked successfully because it contains many of the
essential elements seen in current scientific struggles, including a
lag between a theory and experiment, pleas for funding, competition
from other groups, originality, politics, experimental verification,
dedication, and eventual triumph. Initial course planning can be
guided with the help of books by Sobel, Sobel and Andrewes, and Dash,
which provide concise and popular adaptations of the longitude
problem. These books lack the scientific details needed for this
course, which are amply supplied by Andrewes. A study of just the
longitude problem alone will generally not fill a course consisting
of approximately 40 lectures. The longitude problem has two very
natural branches, one into celestial navigation and the other into
the science of timekeeping.
The course itself is also full of basic astronomy and physics; it is
quite fun to teach and lots of demonstrations from a physics
department demo-room can be used.
In recent years, I've embraced the idea of using computer graphics
in freshman physics. Here's a book I published about it all.
Unfortunately, I do not use this method at Cal Poly at the moment. Although I think this
computation/animation method is single handedly the best way to teach and inject
life into poor old introductory mechanics classes, adapting it to a given student body
is rather tricky. Students at Cal Poly, for example, seem to rather want to stick
to paper and book physics. It is something I need to spend more time working out before doing this
again. If you want to look, the website that drives the whole this is Physgl.org.
I wrote with M. Moelter made the cover of the American Journal of
Physics for March 2013. Wow!
SCM-302: Learn by Doing Lab (LBDL)
Spring 2018: Students needed! Sign up for Bensky's Fri 9am-12pm SCM-302 lab. Teach electronics to 5th graders using PLAYDOH!
All majors and levels are welcome.
No experience with teaching, science, or electronics is needed!
We'll tell you everything you need to know!
All logistics (kids, rooms, materials, etc.) are taken care of. You just have to show up!
No books, homework or exams!
2 units CR/NC.
VERY UNIQUE experience for your resume or grad/med. school essay!'
"Give back" to the community by sharing your knowledge with young students!
Questions? Contact Tom Bensky at firstname.lastname@example.org.
Scroll down for pictures of what you'll be doing.
As part of Cal Poly's CESAME program, we developed a "physics
learn-by-doing lab" that we started running in the Spring of 2012. The
target audience for the lab is 3rd - 5th graders. It involves
building electronic circuits using Play-Doh.
Why Play-Doh? A while back, I saw a Ted talk on "Squishy Circuits,"
which uses conductive properties of Playdoh (yes Playdoh) as a platform
for building simple circuits.
Playdoh itself seems like a perfect "in"
for this age group, so it seemed like a good idea for this project. So,
using my favorite electronics retailer (Allelectronics.com), we stocked up on every
interesting electronics component I could find (potentiometers, LEDs,
switches, motors, buzzers, etc.). With this, 10 kits were made, which
can be handed out to the kids when they visit. Here are a few pictures.
(This entire effort has been published here.)
You (blue coat) and the kids (white coats)
Winter 2019: LS-305 Project Based Learning in STEM Education
3D printing, Arduino, Coding and Robotics
Learn about using the "maker movement" in K12 education.
Open exclusively to LS majors.
No experience needed.
All lessons are hands-on, "learn by doing."
We'll teach you everything you need to know about making cool STEM projects.
Class focus: give you skills and ideas for your own STEM classroom someday.
Think of your resume with "3D printing, Arduino, Coding and Robotics" on it!
Final project: Develop a STEM curriculum package for your future teaching grade level!
What is this stuff?
Coding is where software comes from, and software is what tells a computer what to do. In this class,
you'll learn how to instruct the computer to do
just what you need it to do. We'll focus on the Scratch
programming language, where you code by connecting blocks like a puzzle, like this:
You'll learn all about coding in Scratch, by making fun graphical-based programs---all by connecting blocks!
Imagine thinking of an object, and within minutes, holding it in your hand! This is what 3D printing is
all about. It is where design enters STEM. 3D printers make objects you design out of layers of plastic. Here is an Eiffel Tower being
3D printing is the ultimate in the maker/creative process, allowing a hypothetical design to become
a real object. Imagine having a future class of yours make their own fidget spinners?!? Or science project parts?
In this class, you'll learn to design an object using TinkerCAD, and see how to prepare it for printing
on a 3D printer. (You'll actually print your design on a real 3D printer too!)
Robotics is the ultimate in taking coding into the physical world. Here, you'll use your Scratch coding skills to
command a robot (here the Finch robot) to roll around the room!
You can use code to change the color of its light, to roll forward, or turn when it hits an obstacle.
You can hardly even think about the maker-movement without hearing the word 'Arduino.'
Here it is:
What is it? The Arduino is a $20 computer with no keyboard or screen. So what good is it? Plenty!
The black rows (with the small holes) are connectors, that wires can be pushed into. The wires can be connected to lights, motors, sensors, etc.
So the Arduino can be made to interact and moderate electrical devices it is
connected to (and buried inside of some cool invention). In this class, we'll even use the Arduino to acquire (then plot) scientific data!
Makers have embraced the Arduino as "brains" for their
inventions: controlling drones, robots, cat feeders, or halloween costumes. Here is TED-talk about it: