Creating a Force Plate Using Items You Might Already Have At Home
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:
- a laser
- a wooden stick
- a piece of paper and scissors
- tape
- a ruler
- a stack of cards
- (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!
-Chris
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3D Model Files for Physics Demos Shown at Physics Northwest
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 www.tinkercad.com.
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
https://www.thingiverse.com/search?q=accurate+pvc+launcher&sa=&dwh=845a0cf491587d2
https://www.thingiverse.com/thing:2647534
https://www.thingiverse.com/thing:2650176
https://www.thingiverse.com/thing:2652281
New video – “Pendulum Energy Lab”
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!
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Today was a beautiful day, perfect for launching the tennis ball cannon on the football field. We had a lot of good shots, and took videos of two of them with an iPhone. The first video was shot from the goal line, and landed in the end zone on the other side of the field. The second shot was also shot from the goal line, but it landed well into the track on the other side, for a total distance of 145 yards!
We wrapped the videos up in the app, and have made them available for student analysis. Enjoy, and please let us know if you are using them in your classes!
New Video Motion Analysis – “Horizontal Atwood Lab”
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 SimBucket.com!
New Video Motion Analysis Apps on www.simbucket.com
We are pleased to announce “Video Motion Analysis“, a new set of apps on www.simbucket.com. 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 www.simbucket.com.
The new Video Motion Analysis section can be found on the www.simbucket.com homepage, or via the following direct link.
https://www.simbucket.com/video-motion-analysis/
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