Teaching physics concepts is a challenge in today’s classroom. How can a teacher present the majesty of physics in an era of decreasing budgets and often inadequate space? All too often, schools and teachers despair of providing legitimate, hands-on laboratory experiences for students because equipment is large and expensive, especially when teaching Newtonian concepts like forces, action-reaction, and statics. This need not be the case. I created a laboratory lesson plan that can make these concepts come alive in your classroom for a cost of just pennies per student (literally!) Below is a written description of the lesson plan. The full lesson plan on video is available here. For a complete understanding of how to create this project, it is necessary to watch the video and read the written lesson plan together.
The lesson is entitled Ten Thousand to One and the goal is to demonstrate to students that the strength of a design depends far more upon the careful application of sound physics principles than it does upon the strength of the materials used. The management of forces and non-moving loads is called Statics. Teachers often struggle to explain and present the concepts involved; this simple project brings these ideas to life in your classroom.
1. Project Description
In physics, Statics is the study of perfectly balanced forces. I have often seen teachers demonstrate this concept by showing a mass hanging from a string. The weight (gravitational force) is the action, while the upward force or tension from the string balances the weight exactly. Because a study of statics is motionless, this demo is about as exciting as, well… a weight hanging from a string. There is no excitement, no student input, no measurement or activity.
Our 10,000 to 1 project is dramatically different. Your students will construct a small, lightweight box using only balsa wood, glue, and tissue paper that will support a load at least 10,000 times its own weight without collapsing. When I tell my students that they are expected to build a box that weighs about as much as an index card that will hold up to 35 kg (over 70 lbs) they often respond with disbelief. “That’s impossible!” is often heard from the back of the room. This project not only brings the physics concepts alive, it forces students to reassess their own abilities and self-image as successful scientists!
The project can be successful at a variety of academic levels. Middle school students can examine load to weight ratios, and calculate the density of this very strong structure (a hex-box is a very low density structure). An interesting cross-curricular activity is to compare the density of the hex-box to that of bird bones (some of the lightest, strongest structures in Nature!). More advanced students can calculate force vectors and even conduct failure analysis after the boxes are crushed. Weaker boxes fail very differently than those that hold the greatest loads!
2. What Does this Lesson Plan Teach?
The 10,000 to 1 lesson addresses a number of educational concepts. The list here includes some of the more obvious, no doubt others will occur to you as you implement the lesson in your own classroom:
- Statics and balanced forces: the successful hex-box must provide a vertical supporting force equal to the gravitational force (often called weight or load) placed upon it. More advanced students can calculate the force vectors supplied by each structural member of the hex-shaped box.
- The strength of a design depends far more upon using physics knowledge and managing forces than it does upon the strength of materials. Students can find real-world examples of structures managing forces in bridges, cranes, highway overpasses, even the structure of rafters in their own attic!
- High strength does not require high densities. Solid wood and steel are strong, but our balsa wood hex box is far stronger. Neither stone or steel will support 10,000 times its own weight without being crushed! Students can calculate the density of the box and compare it to the total load carried. Similar calculations could be made for bridges and buildings with a bit of research.
- Structural shapes are not all created equal. Triangular shapes are the strongest for supporting vertical loads, because they cannot fail by shearing – that is, a rectangle can be ‘sheared’ and collapse into a parallelogram without breaking any of the sides – triangles cannot do this!
- One of the most important lessons of the 10,000 to 1 project is Craftsmanship. Nature cannot be fooled, and precise measurement, accurately following instructions, careful planning, and neatness are all rewarded in the most immediate way possible with success in friendly competition with classmates and friends. Just as importantly, every student can achieve and experience this success!
3. Recommended Age Range
Students as young as 11-12 years old have completed this lesson successfully, but this is typically a high school level activity for 10th – 12th graders. When performing this activity with younger, less experienced children, smaller groups and more adult supervision are highly encouraged.
This lesson necessitates the use of sharp instruments (X-acto blades or similar), and ‘superglue’ (cyanoacrylate adhesives). While it is possible to do the project using white school glue, this slows down the pace of building the project substantially, and actually makes the final stages of the project (assembling the box) more difficult.
4. Materials Needed
1. 1/16x 1/16x 30balsa strip (1 per group)
2. X-acto knife or single-edge razor blade (1 per student or 2 per group)
3. 12x 12square of tissue paper (1 per group)
4. 12x 12square of wax paper (1 per group)
5. 12x 12square of cardboard or foam-core (1 per group)
6. ½ oz. Bottle of cyanoacrylate (‘superglue’) adhesive (1 per group)
7. Paper plan to build from (1 per group)
8. 1 Rubber Band (dental rubber bands are best if you can find them)
9. Fingernail file or sand paper
10. A stack of identical textbooks
5. Suggested Lead-in Questions for Teachers
- What makes a strong structure able to hold up large loads?
- How would you design a structure capable of holding up to 50 lbs (25 kg)?
- What materials would you use to construct such a structure?
- Look at a bridge or crane in real life – what shapes and structures did the builders use to create strong, lightweight structures?
- A strong structure, such as a bridge or building, can support more than its own weight. Are there limits to such strength?
- How many times its own weight can a structure support?
- Could you build a structure that would support ten thousand times its own weight?
6. Project Procedure
Part 1: How to Build the Hex Box
1. Tape the hex-box plan to the cardboard, then cover with waxed paper and tape that down as well. Your piece of cardboard must be flat.
2. Start with a 1/16th x 1/16th balsa strip. Place the strip over the plan, and cut the pieces out exactly the same size and shape as shown on the plan. Use an X-acto knife or single-edge razor blade, and make sure your cuts are square (perpendicular to the table surface!)
3. Once the pieces for one hex shape are cut out (8 pieces), use sewing pins to pin the pieces down to the cardboard directly over the plan as shown below. Note that the pins do not puncture the wooden pieces; instead, two pins scissor together to hold the wooden pieces in place!
4. With all eight pieces pinned down, use a drop of super glue on each joint where wooden pieces come together. It may be helpful to put a larger drop of glue on a piece of foil or waxed paper and then use a toothpick or a scrap of balsa to “dip-and-dab” glue into place. This often prevents over-gluing which actually weakens the final structure.
5. Allow 10 minutes for the glue to set completely. Don’t hover over the work and blow on it to help it dry. Cyanoacrylate glues ‘cure’ by a chemical reaction – they don’t dry at all. The vapors from curing superglues can be very irritating to eyes or nose so beware! Responsible adult supervision is a must!
6. Once the hex shape is dry, lift the waxed paper off the cardboard. You should be able to peel the waxed paper away from the hex shape just like peeling the backing off of a sticker! Set this hex-shape aside in a safe place.
7. Repeat steps 1-6 to produce a second hex-shape. These will be the top and bottom of your structure.
8. Use the remainder of your 1/16th x 1/16th balsa strip to make six spars; these will be the sides of your hex box.
9. Once you have cut out six pieces, use a small rubber band (dental rubber bands used for braces are perfect for this!), or tie the six pieces together by wrapping them with a piece of thread.
10. With the six pieces fastened together, sand the ends lightly so they are all exactly the same length. A fingernail file is excellent for this purpose!
11. The vertical spars must now be glued in place. Put one of your hex-shaped pieces on a sheet of waxed paper. The spars must be glued at each corner or ‘vertex’ of the hex. Place a small drop of glue on the corner, and press the spar carefully into place keeping the vertical hold in place for 5-10 seconds.
12. Once all six spars are glued in place, it is time to attach the second hex-shaped piece. Place the unattached hex-shaped piece on a waxed paper sheet, then place the hex with the spars on top of it. Repeat the procedure from step-11 and attach each spar to its corresponding corner on the second hex-shaped piece.
13.The last procedure is to add the diagonal braces. Each side of the hex-box is a square and squares are structurally weak. It is easy for them to collapse. By installing a diagonal brace, the square becomes two triangular shapes and it also becomes much stronger!
14. Begin by cutting one end of a balsa strip at a 45-degree angle (just like the diagonal pieces on the hex-box plan)
15. Fit the strip into one corner of the hex-box, and use a pen or pencil to mark the correct length for the brace. Use an X-acto knife or similar to cut the brace to the correct size.
16. Glue the diagonal brace into the hex-box and allow it to dry. Repeat steps 14-16, installing a diagonal brace on each side of the central cube of the hex box. With all four braces installed, the hex-box structure is now finished.
17. The last step is to cover the finished box with tissue paper. Any common gift tissue is acceptable.
18. Cut out a piece of tissue 1-2 inches larger than the hexagonal side of the hex box. Use white glue, thinned slightly with water, and moisten the entire top of the hex box. Immediately place the piece of tissue on the box and smooth it down with your finger. Allow it to dry completely, then trim the excess tissue away with an X-acto knife or similar. A new, sharp blade will be very helpful here. Please note that you cannot successfully trim the tissue if the glue is not totally dry!
19. You may notice that there are a few small wrinkles in the tissue after you finish don’t worry! we will remove these wrinkles in the last step!
20. Repeat step 18 for the second hexagonal side of the hex box. Allow to dry completely, and trim it carefully.
21.Use a strip of tissue long enough to cover three sides at once, and glue in place and trim as above. Repeat and all sides of the hex box are now covered with tissue.
22. Make sure the box is totally dry, then moisten all sides with a spray bottle. An old glass cleaner sprayer filled with water works fine here. The paper will become slack and loose.
23. Hold the box by the corners until the paper dries; this will take only a few minutes. Fresh air and sunshine, or if you must, a hair dryer are helpful. As the paper dries, it will shrink slightly, stretching out any wrinkles and leaving you with a smooth, professional finish.
24. Your finished hex box is now ready for testing!
Part 2: How to Test the Hex Box
1. Each box must be weighed before testing. Use a scale that can measure to at least 1/10th of a gram (± 0.1 g) and record the mass of the hex box.
2. Place the box on a steady, flat table and add weight until the box fails and collapses.
3. Method 1 for Testing: Using text books. Stack each book carefully, being sure to center each one so the entire stack does not tip in any way. Allow a few seconds between each book to be sure the box is holding firm.
4. Use several books to find the average mass for the books and then calculate the total load the box held successfully. The ratio of the (load mass/box mass) is the score. A minimum score of 10,000 to 1 is considered acceptable! The student who’s box has the greatest load/mass ratio wins!
5. Method 2 for Testing: Use a large cake pan and dry sand. Begin by balancing an empty deep dish cake pan on the hex box. Slowly add sand to the center of the box, pouring or scooping sand in slowly until the box collapses from the load. Weigh the pan (including sand) after the box fails. Calculate load/mass ratio as above.
7. How Does it Work?
Medieval builders used strong materials to build strong structures. A castle made of stone was heavy and costly to build; thick walls made for safety seriously reduced the amount of useful interior space within the building. Modern builders do not rely upon heavy stone or brick for strength in a building; instead, we use our knowledge of structures and forces to make buildings stronger and more efficient.
Building a strong, low density structure means that we can use fewer materials to construct a building than our ancestors did. Reducing the amount of materials required for a given engineering job makes our buildings and other civic structures greener and more environmentally friendly. It also helps those who pay for these structures reduce costs without compromising the utility of the structure.
Modern engineers use their knowledge of physics to manage load forces and create lightweight, strong structures. The study of unmoving loads and forces, and the structures that support them is a branch of physics called Statics.
Good design can enable a structure to support hundreds, even thousands of times its own weight. Such structures must be low density, in order for us to make use of the interior space. A building or bridge that could support great loads would be of little utility if the interior space was extremely limited.
The hexagon is prized in engineering as a space filling shape. A repeating pattern of hexagons is often used to make a strong structure that will resist changes in shape under great stress. Bees making honeycombs are one of the most common examples of the use of hexagonal structures in nature, geometrical crystals (such as snowflakes) are another.
Triangular shapes are the strongest. Engineers use them in buildings, bridges, cranes and other high strength structures. The diagonal supports in the hex box create strong triangular shapes that help the box support great loads.
8. Project Follow-Up/Additional Activities
1. Have students calculate the average load capacity of the hex boxes from the accumulated class data. A winning box in my class usually has to hold 25-30,000 times its weight! The average 2-gram (1/15th oz) box can hold a 50 pound load easily!
2. How many boxes would it take to hold a student up? An array of six boxes underneath a cookie sheet should be able to hold up almost any student or adult. The trick, of course, is to stand on the cookie sheet and keep your weight vertical without shifting from side to side. Apply your weight slowly and smoothly as you stand. This makes a great demonstration for back-to-school night or parent night activities!
3. Have students examine the structure of bridges, cranes, and high rise buildings as they are being built. Compare the use of triangles and reinforced structures in professional engineering to our little hex box. This is a wonderful internet-search activity!
9. Experiment Photos and Videos
Please see below for the full lesson plan on video.
Sharp objects are required. This lesson plan is not for students under age 11.This lesson necessitates the use of sharp instruments (X-acto blades or similar), and ‘superglue’ (cyanoacrylate adhesives). The vapors from curing superglues can be very irritating to eyes or nose so beware! Responsible adult supervision is a must!