Creating a Force Plate Using Items You Might Already Have At Home

Category : High School, Middle School, Physics · No Comments · by November 19, 2020

Making a Homemade Force Plate

Staying home during COVID means teachers and students have to get creative.  Things that you would normally have at school you might not have at home and vice versa.  A few days ago I decided to see if I could make a homemade “force plate” that could accurately measure impact forces.  My smartphone has a high speed camera.  I just needed something that was sensitive enough that it could measure tiny forces happening over very short periods of time.

My solution is shown above.  To build it you will need:

  1. a laser
  2. a wooden stick
  3. a piece of paper and scissors
  4. tape
  5. a ruler
  6. a stack of cards
  7. (optional) a small kitchen scale to calibrate your force plate

Assemble your force plate as shown above.  Adjust the height of the stick such that the laser beam hits the middle of it.

Using the Homemade Force Plate

To measure static forces, press on the plate.  As you press the laser beam will move across the stick.  You can use a ruler and some known weights to calibrate your stick.

Measuring Impact

To measure impact, download a suitable video analysis app to your smartphone.  For iPhones and iPads the “Technique” app by HUDL works well.  I used Technique and a homemade force plate to create the latest Video Motion Analysis activity, “Measuring The Force Of Impact Over Time“.  In the activity students learn how padding minimizes the force of impact.

Feel free to share and comment below!


All ChemThink Tutorials are Finished

Category : High School · No Comments · by April 15, 2020

“Chemical Reactions” and “Isotopes” are ready!

With the addition of the last two tutorials, all of the original ChemThink tutorials are now complete.  Now that they are HTML5-capable they will run in any modern browser.


It has been 4 years and 2 months since I started working on “The Particulate Nature of Matter”.  I feel like I just finished my dissertation.

Please spread the word that the original ChemThinks are all complete!

Also, I doubled the number of server CPU cores and RAM to support the increased usage over the next few months.  This cost several hundred dollars, but it is worth it to minimize the amount of friction for students working on ChemThink from home.  If you haven’t done so already, please consider donating on

-Chris Bruce
Physics Teacher, NBCT
Lead Developer,

“Ionic Formulas” has been converted to HTML5!

Category : High School · No Comments · by November 8, 2018

It has been a super-productive week, and I just finished the port of “Ionic Formulas” from Flash to HTML5.  The new HTML5 version is identical to the Flash version, and shows how we name ionic compounds.  Because it runs in HTML5, it should work on any modern browser.

If you have already donated to the site, thank you!  As of the time this writing, we are almost 80% of the way to our yearly goal of $2500 to keep the site running.   If you have not donated yet, please consider donating., ChemThink, and rely on your support to pay for the cost of their web server.

Donate Today!

3D Model Files for Physics Demos Shown at Physics Northwest

Category : High School, Middle School, Physics · No Comments · by November 17, 2017

We had a great evening of physics demos and discussions on Wednesday night.  Thanks to Marty (CHS), Dave (CHS), Caleb (CHS), Josh (PMSA), Kunal (HPHS), Bryan ( GBN), Mark (PHS), Mike (SHS), and Sasha (Northwestern University) for sharing.  The hosts were excited to give away 3D printed models of the “Accurate PVC Launcher”, “Moment of Inertia Spinner”, “Cheap Pulley”, and “Adjustable Frequency PVC Horn”.  All of the designs were built using the free website

If you have access to your own 3D printer, you can print your own!

Click on the images below for the model files and instructions for printing the “Accurate PVC Launcher”, “Moment of Inertia Spinner”, “Adjustable Frequency PVC Horn”, and the “Cheap Pulley”:

Adjustable Frequency PVC Horn on Thingiverse by David Torpe

Moment of Inertia Spinner on Thingiverse by Chris Bruce

Accurate Ball Launcher PVC on Thingiverse by David Torpe

Cheap Pulley on Thingiverse by Caleb Cochrum

New video – “Pendulum Energy Lab”

Category : High School, Physics · No Comments · by November 9, 2017

For the past few years in our regular physics classes, students have struggled to complete the “Pendulum Energy Lab”. This lab involved setting up a mass hanging from the ceiling by a string. Students were asked to shoot video of the mass as it swung back and forth. They then analyzed the video to compute potential energy and kinetic energy at various points during the swing. The problem was that to get the height and speed, they would have to set up multiple meter sticks at lots of different crazy angles, and then have to deal with blurry video. The lab that was designed to show a simple concept ended up being so complicated and taking so much time that most students completely missed the point.

This year we decided to shoot high-quality video of the lab to see if we could distill things down to their essence and eliminate the blurry meterstick mess.

The result is the new “Pendulum Energy Lab” video. Students must still measure height and speed, but this time the measuring devices are perfectly positioned and are easy to read. Students can easily scroll through the video to record height, position, and time. We have included a paper copy of the activity which prompts students to create a data table for potential and kinetic energy at various points, then to create energy bar graphs.  We are looking forward to trying the new lab in class on Monday!

New Video Motion Analysis – “Horizontal Atwood Lab”

Category : High School, Middle School, Physics · No Comments · by September 25, 2017

We just finished uploading six (really five, because we were able to reuse one of the scenarios) new high-speed videos for Video Motion Analysis called “Horizontal Atwood Lab”. We also put together a very simple lab activity to go with it, suitable for an introductory high school physics classes. In the activity, students analyze sets of three videos to determine the relationships between acceleration and total mass, and acceleration and force. Students should be able to finish the activity in about 30 minutes.

Now that the analysis apps are built, shooting new videos and uploading them goes fairly quickly. Let us know if you have any videos that you would like to see for your class!

Video Motion Analysis – New on!

Category : Biology, High School, Middle School, Physics · No Comments · by September 20, 2017

New Video Motion Analysis Apps on

We are pleased to announce “Video Motion Analysis“, a new set of apps on  Each app features one video shot with a high-speed camera.  Students can scroll through each frame and take careful measurements.  Some of the apps contain more advanced plotting, graphing, and analysis tools so that students can collect, plot, and analyze the data directly within the app.

We tried the “Ball Launched At An Angle” videos today with our students.  Using the graphing and slope calculation tools, they were quickly able to determine that horizontal acceleration is always zero, and vertical acceleration is always 9.8 m/s² downward, no matter which videos they selected for analysis.

We are continuing to shoot video, and hope to have many more videos available for analysis over the coming months.  If you have a physics lab that you do with your students and would like us to shoot video, please let us know.  We will do our best to recreate it for you and make it available on

The new Video Motion Analysis section can be found on the homepage, or via the following direct link.

The HTML5 version of “Atomic Structure” and the status of the Chemthink HTML5 port

Category : High School, Middle School, Uncategorized · (6) Comments · by April 8, 2016

HTML5 ATOMIC STRUCTURE is pleased to announce that the HTML5 version of the Chemthink “Atomic Structure” tutorial and problem set is now online.  Because the new version is designed from the ground up for HTML5, it means that students with iPads, iPod Touches, or phones can now run the tutorial in a browser without needing an actual computer.  In 1:1 classrooms, this means students won’t need to go to the computers to log in.  It should take approximately five minutes less to get students up and running with the tutorial.

Atomic Structure

Click the magnifying glass to go to the Chemthink “Atomic Structure” tutorial


In creating the HTML5 version, I tried to stay as faithful as possible to the original Flash version, only adding or making changes where it made sense.  For teachers, this means any worksheets or activities you created based on the original should still work with the HTML5 version.

When a student clicks to launch the app, they are presented with a choice between the tutorial and the problem set.  In practice, I have found that it is easiest to tell my students to open up and run the tutorial in one browser tab while running the problem set in another.  If a student misses a question, I tell them to find the answer in the tutorial before clicking the “continue” button.

Because there is no student login required, students are able to get started very quickly.  This also means that students will need to show you when they are finished with the problem set.  I have included a large gold star on the completion screen so that you can very quickly glance at a student’s screen to see that they are finished.  For students completing the problem sets at home, I have asked that they take a “selfie” with their completion screen.

Because of the amount of class time I have saved by not requiring a log in, I am strongly considering permanently eliminating the need to log in.  The drawback to not requiring students to log in is that teachers will have no ability to track student progress, other than physically observing their students’ screens.  If you can’t live without the student tracking feature, please speak up!


From start to finish, the “Atomic Structure” HTML5 port took 12 days to complete.  I am hoping that I can maintain this pace for the remaining 9 tutorial/problem sets, plus the “Chemical Reactions” lab simulation.  At this rate I should finish everything in about 20 weeks, roughly around the beginning of September.

What would you add or change about Chemthink?

Category : High School, Middle School, Uncategorized · (2) Comments · by March 22, 2016

I’ve begun the process of rewriting Chemthink from scratch. At this point I’m looking at reusing all of the existing animations and texts, but we have an opportunity to make the suite of tutorials, question sets, and virtual labs even better. I can’t promise anything because I have only a finite amount of time to finish the project, but I would like to open things up for input from Chemthink users.

So far, the to-do list includes:

  • Recreate all tutorials, problem sets, and labs in HTML5 so they run on mobile
  • Rebuild the user database so that teachers can create and manage classes and students can log in and track their progress

If you could change anything about Chemthink, what would you change?

If you could add any capabilities, what would you add?

The Chemthink Problem Sets are Now Available!

Category : High School, Middle School, Uncategorized · (1) Comment · by March 10, 2016

A few weeks ago I posted 8 of the original Chemthink Flash tutorials. I am excited to announce that the Chemthink problem sets are now available for these tutorials!  The question sets require students to answer a certain number correct before they miss a small number of questions.  As a result they are fairly difficult.  If students struggle on a problem set, they are encouraged to take a look at the tutorial again.

There is no server backend, so if you want to keep track of which problem sets or tutorials you or your students have completed you will need to take a screenshot of the completion screen.

Tutorials and their corresponding problem sets are now available for the following:

The Particulate Nature of Matter
Atomic Structure
Ionic Formulas
Ion Formation
Gas Laws
Covalent Bonding
Ionic Bonding
Molecular Shapes

In addition, over the next few days I post two more problem sets without tutorials: “Chemical Reactions” and “Isotopes”. At the moment the tutorials for each of these are nonfunctional, but I will do my best to get both the tutorials and their question sets working as soon as I can.

Edit 3/10/2016 – All 10 tutorials and problem sets are now available, including “Chemical Reactions” and “Isotopes.


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