Popsicle Stick Tower
12th grade Physics class exercise:
Given 200 Popsicle sticks, build a tower at least one meter high that can support 10 Physics books. The record for this Physics class is 18 books, approximately 72 pounds.
Can it be done? Can one support more than seventy pounds of books with a Popsicle stick structure?
You betcha', here's how we did it...
- Any and all projects should begin with research: We looked at numerous web sites trying to gain insight and inspiration from other people's past experience. This project is a common Physics class challenge, surely it is documented. It was, but not to well, so this page was created to add some specifics to that documentation; here is one answer. Can you use a limited set of resources to create something that is astounding???
We visited many web sites and saw a short boxy design on one that could be adapted to fit our needs (which were for a much longer tower). The details were lacking, but the basic box of sticks was visible. We also saw an educational TV show about the Comstock Lode (a major silver mine) and a German mining engineer who developed the "square sets" that allowed miners to extract the ore while preventing collapse of the mine. We refer to another source of information....
Philipp Deidesheimer was a graduate of the Freiberg School of Mines, the world's foremost institute of mining technology, a science that Americans were just beginning to grasp. He had been practicing his profession in California for several years. After only weeks on the Comstock sites, he developed a new system of "square set" timbering, a deep-mining support technique so effective it opened the Comstock to far greater penetration and was instantly applied across the West and worldwide.
The "square sets" were large interlocking timbers that were added on to in a cubic arrangement to as the miners dug away at the ore body. This was enough inspiration to get us started. We knew we could make a stable, extensible, interlocking structure that could support tremendous weight from simple box like forms.
- The modular, interlocking approach seemed easiest to build and replicate; the most logical approach given the task. Our design allows each load bearing vertical beam to abut against a horizontal cross member. Each "tongue" from the above cube fits into a groove on the adjoining cube. This allows it to bear weight without slipping to the side and busting the joint. Each member of the stack interlocks and each load is borne on a bottom member that has it's weight horizontally distributed. This structure prevents twisting and allows stacking by distributing the load from each module on horizontal beams of the next module.
- Stick alignment and uniform stick offset was critical; the parts must all measure the same. Uniform units are mandatory. Make each unit as square and regular as possible.
- Since we were dealing with wood, we used Aliphatic Resin; Elmer's® Professional Carpenter's Wood Glue by Borden®. Others in the class used "tacky glue" and hot glue with lesser success; use the right glue for the job!
- Each leg needs to be 10 sticks high (yielding 1.05 meters total height for our tower)
- To arrest torsional twist, cross braces are necessary, even sturdy legs may collapse due to twisting. Most towers we see have cross bracing, so this is a well known and recognized method of solving the problem of shear twisting under vertical stress. Learn from what has gone on before you.
- Read the instructions on the glue. Follow them. It says to clamp in place until dry; we did this with weights (rocks) when building the flat modules and with clothes pins when assembling the modules into a tower. Attention to the basic principles ensures success of the final project.
- Some contests limit the amount of glue, this one did not, so glue was applied generously; multiple times for every joint. The abundance of glue ensured that the sticks would break before a joint came undone.
- Rather than measuring things, we decided to use a 1 PSWU (Popsicle stick width unit) standard for aligning the sticks. This provided a consistent measure for gluing guidelines and stick placement.
- Give yourself plenty of time; begin work on the assignment as early as possible. If things go awry, you can still adapt and change the design. Glue takes a long time to dry. Depending on your work area, maybe only a few modules can be under construction at a time. You also want a day or so for the final gluing to completely cure.
- We got better and better at building the boxes as we gained experience. This means that some of our earlier boxes were "less precise"... If we had unlimited Popsicle sticks some of the early boxes would have been rebuilt.
- Make squares. Each glued joint is one Popsicle stick width from the tip of the stick. To align the sticks and ensure "squareness" we used several rocks slabs that I had in my collection (I am a Geologist and have collected numerous building stone examples), you may use a builder's square or other straight edges for alignment. We laid the sticks out two-by-two and glued only the second stick, removing the outer-most one before the glue set for our base units.
- Once the glue dried on this basic square, a cross brace was diagonally fitted. We had to make sure this brace was either inside or outside depending on the module we were constructing. This becomes clear when you start building (we did make a few "false starts" in the beginning).
- When two squares with opposing cross braces were glued and dried, we joined them with horizontal "tiers" to form a cube. First two bottom sticks were glued, weighted, and allowed to dry, then the structure was turned over and two sticks were added to the opposing side of the cube.
- A cross brace was glued diagonally across these sticks (weighted in place and allowed to dry).
- A cube is born. There are two interlocking types; an "inside stick cube" and an "outside stick cube". These alternate in the tower structure. The load bearing (vertical) sticks rest directly on horizontal sticks.
- The cross-braces on the second module were designed to be counter (opposite) to those on the first module. If the first module can be though of as having Z braces, the second module can be thought of as having S braces.
- Our first cube was so poorly aligned and the cross braces were not installed correctly for extensibility; they would not interlock symmetrically. We broke the sticks apart before the glue had set to it's maximum and recycled these sticks later in the process. Elmer's Wood Glue makes a bond that is stronger than the wood itself, so salvaging a bad module had best be done before the glue is fully cured. Care must be taken to avoid busting the sticks instead of the glued joint (a kitchen knife and gentle persuasion helped).
To re-cap: make square frames, join the squares into cubes, join the cubes into a tower... simple enough huh?
A picture is worth a thousand words. Here are a few thousand words....
The basic building unit; each glued joint is one Popsicle stick width from the far tip of a stick. Notice the cross-brace is on the underneath side of this square. There are "overs" and "unders" in this building process or "insides" and "outsides" in the stack.
One being glued (under rock weights), the basic materials, and the first few square sets.
Joining two end sections to form a box.
The rocks act like clamps to ensure a strong glue to wood bond.
Modules assembled, clamped and drying; tower assembly 8 out of 10 stacked.
The clothes pins act as a clamp while the leg joint glue sets up.
Leg joint detail. Notice the double sticks, outside for the top box,
inside for the lower one. Also notice the abundant glue!
The weight! A physics book, approximately 4 pounds each.
How many physics books can be stacked on the tower???
Our first attempt was 26 physics books; just to out do a classmate's (Manuel) 25 books... No problemo. This tower beat the best hands down, what else can this tower hold?
We quickly ran out of books so the teacher suggested putting students on it instead. First was Katie (approximately 105 lbs). She noted creaking, but the tower stood tall.
We then substituted another female student named Cassie (approximately 110 lbs). This tower easily supported her weight.
We then substituted another student, Blake (approximately 150 lbs). No problem, this tower can take more weight than that.
Then Mr. Akines; the Physics teacher himself. Approximately 200 lbs. Tower still stands unphased.
Then Zack; approximately 230-240 lbs. Still standing undaunted.
Ultimately we got the biggest person available, a football player nicknamed "Big John" at 285 lbs sit on it... The tower is still standing tall.... John is weighs the equivalent of about 71 physics books. We have exceeded the record (18 books) tremendously.
We ran out of time before we could find new or inventive ways to destroy the tower... it came home intact and we have yet to make it fail or push it past it's weight limit... but we plan to.... bwa-ha-ha-ha.
In the end, this design scored a total of over 712 points out of a possible 100 for the test... surpassing by far the original goal and everyone's imagination. It created a minor school disturbance as other classes in the hallway had to come and see what the fuss was all about. All were astounded.
How much weight can a Popsicle stick tower support? We have yet to find out what it will take to exceed the limits of our modular square-set cross-braced structure.
Hopefully this page will help guide you in besting our attempt to find the structural limit of glue and simple Popsicle sticks. It has got to fail somewhere, we just have not found that limit yet.
Best of luck in your project. I hope this page has been helpful in exceeding your Popsicle stick tower goal. Let us know by an email to phillip"at"philliphansel.com
if this page has been a help to you.
Created on ... December 13, 2004
By Mr. Phillip Sand Hansel II and his wonderful son