A Fresh Take on Catapults in the Classroom

This is a complete lesson plan for middle school students (grades 6 - 8) that incorporates multiple practices in engineering, technology, and mathematics. Students will:

1. Make accurate metric measurements
2. Use basic tools to build a final project
3. Assemble and manufacture a final product based upon previously drawn blueprints
4. Test, modify, and retest a manufactured product to improve the overall result
5. Identify and model both precision and accuracy
6. Calculate average
7. Graph both individual results and classroom results
8. Reflect on final results of a completed project

Sam (12 years old): "Yeah, I hit Mr. Stark right in the face with a mini-marshmallow!"

Mom (38 years old): "Wait... you did what?"

Sam: "My group shot marshmallows at Mr. Stark's face since my group built the most accurate and powerful catapult in class!"

Mom: "So, did he know that you were going to launch marshmallows at his face, are you in trouble?"

Sam: "Nope! But we would have gotten a bunch more points if he ended up eating it."

I only hope that there are conversations like this around the dinner table when my students go home after a science class. I love getting my students excited about science and engineering and love it even more when they bring that excitement back home with them. One of the tried and true lessons that kids love is building catapults. I have been doing some iteration of this lesson for the past eight years and I think that this final, most recent version has so much value for a STEM based classroom. I wanted to share the way that I teach this classic lesson and show you some of the new ideas and methods I use to make it a truly memorable experience for my students. From my parts purchasing system to the final awards, I have some cool ideas that will help launch your next catapult project!

Supplies to Build the Catapults:

Large Popsicle Sticks

Small Popsicle Sticks

2x4 Blocks of wood

Pushpins

Rubber bands

Pipe Cleaners

Masking Tape

Duct Tape

Hot Melt Glue Sticks

Plastic Spoons

Skewers

Tools to Build the Catapults:

Dremel with grinding bits

Drill with various drill bits

Hot Glue Guns

Box / Miter Saw (handheld)

Other Materials and Supplies Needed:

Sharpies

Gallon Sized Ziploc bags

Opening presentation for students

Student worksheet while designing, building, and testing the catapults

End of lab graphing activity

Graph Template Sheet

Keep track of student scores and averages

Carnival tickets

There are two main goals for each group. The first is to be able to build a launcher that can launch a mini marshmallow an average distance of 3 meters (over five attempts). The second is to shoot at least one mini-marshmallow (out of three) through a target set up three meters away from the launcher. Therefore, the catapult must be both powerful and accurate!

One of the things that sets this project apart from other catapult projects is the overall variety you get with each group's catapult build. This is entirely due to the variety of materials supplied to the students to build their launchers. Each group is started off with an identical ziplock bag of materials; a pipe cleaner, three large Popsicle sticks, a rubber band, and ten tickets. The students are able to use the tickets to purchase any additional supplies they may need from the "Melted Marshmallow" storefront. Before they are allowed to buy materials, they need to first come up with a finalized design of their launcher. I usually have them do this in two parts. First I have each individual student create a sketch of what they want their launcher to look like and describe how it will function. This is done after we have gone through the entire introductory presentation. From this point, students are organized into groups (two to three students) to begin the next process. The Student Sheet is distributed to each student and then they begin the collaboration process to determine what the group's final design will be for the catapults they will build. They draw this fully labeled design on the student sheet and give a list of all materials they need along with tools they will need to use. Once groups have their design completely figured out they can come to the storefront to buy the specific materials they need to build their launcher. But before any of that happens, you'll need to get everything together!

I have found that the best method for organizing all of the materials is to put all of the group's initial materials into ziplock bags. I have five classes and typically have between 8 and 12 groups per class. To organize sixty groups of materials I end up just laying out piles of each group's initial materials and the I stuff them all into the ziplock bags to be distributed when the students are ready for them. All of the additional materials I organize in repurposed containers (Trader Joe's cat cookies and animal crackers!). This makes things a bit more logical and organized while all of the building and testing is going on in class. A few minutes before the end of the class I go around the room with a roll of masking tape and ask the groups to come up with a short name for the their group. I write this, along with their class number, on the piece of tape and have them stick it to their bag so that they will be easy to recover in the next couple of classes. Using the gallon sized ziplock bags allows even the biggest launchers to be put into the bags so that things stay super organized throughout the project.

Now that you are all organized and ready to go it's time to build!!

I love having students use tools in my classroom. Ultimately, I supply all of the tools but I typically use doubles of tools I have in my wood shop. All students must wear safety goggles when using drills, dremels, and saws. To help minimize cords and tools around the classroom I put the drilling tools, cutting tools, and glue guns at three different stations. I also use a simple system to ensure that there are not too many students at a work station at a time. I use passes for each station so that only one or two groups can work at a station at a time for five minute intervals. I laminated magnets to the back of the passes so that they can be stuck to my white board when students are done using the passes.

The students use all of their purchased materials along with their final sketches to build their launchers. I do a little mini lesson on how to use various building techniques that work well. I explain how to use the pipe cleaners as a method to affix two popsicle sticks to each other. I also show them how to make a saw kerf where the popsicle sticks can slide into (like a mortise and tenon). I also explain how to properly use hot glue so they don't use up their precious resources. The best part of the "pay to build" method is that it encourages the students to be more careful when using their materials since middle school students often will waste materials in my class. It also encourages them to be resourceful with what they have encouraging them to solve the little problems they will run into (i.e. how do we make the stopper bar adjustable?).

By the end of the project you will hopefully see myriad launchers with various aspects that make them better at one thing or another. It's fun to set all of them out on the table and have a large discussion about some of the various aspects that are common throughout the launchers (i.e. lots of spoons) and some of the distinct differences (i.e. base of 2x4 or popsicle sticks). Students are encouraged to test their launchers out while they are building them. I have designated a specific taped off area in my room where they can practice launching mini-marshmallows (two shots and then back to the building). They MUST wear safety googles during the launches just in case one of the launchers fail catastrophically and fling debris into the air and at someone's eyes.

I have students test on a desk that we use for the final launching. This year I had students do their final launches outside since most of the launchers were powerful enough to reach the end of my classroom. This also helped minimize the amount of little gooey globs of sugar stuck around my classroom... I don't know if the animals enjoyed them or not when we launched them outdoors :)

Students keep track of the distances and make some qualitative observations about each launch using the student worksheet they first used to create their final design. They also will keep track of the other group's averages and some qualitative observations about how their launchers worked. The goal is for the students to be able to reflect back on both their launchers performance and the other group's launchers so that they can compare and contrast them. They will use the distances for the final lab assignment where they will graph the results for their class.

For the accuracy and precision component of the testing I created a large target made from a piece of thick cardboard. I made the circle 40cm in diameter and made it so that it hangs from the ceiling using some string and a couple of binder clips. I also made it so that it is at a height where I can stand behind it and have my face lined up right in the middle. You can see in the pictures that my assistant principal is standing on a crate so she is lined up with the target. The winning group from each class (they have the highest overall score, as explained in the opening presentation) gets to launch three shots at me (or another lucky adult) and for each one that I eat (don't worry, they are new marshmallows and the kids washed their hands!) or get hit in the face with they get extra points to supplant last year's ultimate marshmallow launcher champions.

There is a winning group from each class based upon how many points they scored in total (once again, check out the opening presentation for details on that). But, there is only one overall winning group from all of my classes. If their overall score is greater than last year's ultimate launcher I mount their catapult on the wall with all the important details (see pic).

This year I decided to do something totally different for the winning groups. I used Fusion 360 to design a little catapult trophy that I printed off with some PLA. The kids loved it, even though it was far from perfect (I am still learning) and I think it was a fantastic way to end a really fun project.

The final step is to have the students complete the end of lab graphing and focus questions activity. I created a graphing template to give to the students but you are welcome to have them figure out the scale of their own graphs if they already have that skill set (and you have the time). The focus questions are based upon both the quantitative data they collected and the qualitative evidence they collected during the testing phase. Since I use this project at the start of the year I am able to use what was taught during the lab throughout the remainder of the year and it really helps that the kids absolutely love the project. I hope you and your students do too!