Center of Mass device

I like to give my students different challenges and let them explore. Here is one such challenge. The idea is to print a number of these containers, which are designed for 16mm diameter steel balls (same as the projectile launcher I use and the moment of inertia discs I designed), and students (or the teacher) can place them at different locations inside of the boxes. Tape the boxes shut so no one can see inside! Students can then take two different measurements.

• What is the mass of the box?
• What happens when I hang the box from a tooth pick? Where is the center of gravity line?

The second group of measurements is why the boxes have 8 holes. Students can make measurements for where the center of gravity is when hanging from the holes. 

Here is a lesson worksheet I made to accompany this model: https://drive.google.com/file/d/1oTp5O8GfO1Zokw1bE1kq_V03sKeVvkxH/view?usp=sharing

This is a good resource for this lesson: https://www.grc.nasa.gov/www/k-12/VirtualAero/BottleRocket/airplane/cg.html

Keep in mind! You want to print in a dark color to keep students from holding them up to the light. You will also want low infill, and probably also best to print in a light weight material. The lines on the boxes intersect at the center of the holes for the balls. The geometric center of the box is labeled with a +. You will need to print them 2 at a time, and I designed them to fit on a Prusa mk3 two wide.

When I originally ran this challenge for my students, I prepared 6 different boxes for them to experiment with. Each had a different orientation, and I varied the number of steel balls, since they would not have a way of figuring out the mass of a steel ball alone.

I hope this is a fun exercise for your students!