Top image: Catapult near Castle Saint-Angel, Italy (photo by jacmac34 via Pixabay)

Setting the Stage

Prior Skills and Knowledge

To successfully participate in this Design & Build, students should be able to use basic cutting tools and fasteners for construction. It is highly recommended that students have prior knowledge and skills related to the use of simple machines prior to participating in this Design & Build.


Throughout history, humans have sought to find ways to get objects over obstacles. This frequently involved using some sort of device to propel the object up into the air and over the obstacle. In medieval times, people developed devices called catapults to solve this problem. Catapults include the mangonel (fulcrum pivots at one end and the force is applied by applying tension to the fulcrum) and the trebuchet (fulcrum pivots at its centre and the force is applied by a counterweight located at the end of the fulcrum). In these types of devices, force is transferred through a mechanical system to propel an object such as a rock (or pumpkin) up, up and away!

This Design & Build challenge provides opportunities for students to predict how a given force affects the distance travelled by an object as well as compare how forces of different magnitudes result in different distances travelled by propelled objected. Students will work collaboratively and develop their Design & Build skills to safely create and test a device which uses simple machines to launch a ping pong ball either a) as far as possible or b) up and over an obstacle such as a badminton or volleyball net.

Trebuchet being made ready for launch
Source: cg2, Pixabay

This design and build could begin from:

  • questions and/or comments that arise after students view pictures of devices such as catapults and trebuchets used in early societies. Discuss using questions such as:
    • “What do you think was the purpose of devices like these? How would their builders know if it was successful?”
    • “How do you think this device works? What simple machines does it use to help it achieve its purpose?”
    • “How did the builders control where the object lands? How accurate do you think they were able to be? Why do you think this?”
  • questions and/or comments that arise after students view videos of present-day catapults or trebuchets (e.g., videos of a “pumpkin catapult” on YouTube).

    Pumpkin trebuchet used at the 2008 Punkin Chunkin World Championships
    Source: GB fan, Wikimedia Commons

    • “What kind of force is causing the pumpkin to move?”
    • “What do you think would happen to the pumpkin if a greater force was applied to the object?”
    • “How could you measure the amount of force that is used?”
  • going on a field trip to attend an event (e.g., a renaissance fair or local pumpkin-throwing contest) where demonstrations of catapults take place.

Design Criteria

As a class, students brainstorm criteria that their prototype ping pong ball launchers must meet. Educators may choose to add other criteria that are curriculum-specific, such as using specific types or numbers of joiners/fasteners, measuring, using specific materials, etc.

Design criteria examples:

  • Must be able to go up and over a badminton net OR must go as far as possible from the starting position
  • Must incorporate a minimum of 2 different types of simple machines
  • Must use 3 joiners/fasteners
  • Must include a way to change where the ball lands (adjust height of launcher)
  • Use minimum of $5 and maximum of $10 when purchasing materials

Materials and Preparation (Click to Expand)


  • cardboard boxes and tubes, various sizes
  • craft sticks
  • cups, assorted, small (e.g., paper, Styrofoam)
  • elastic bands, various sizes
  • fastening materials (tape, glue, etc.)
  • paper (construction, cardstock, etc.)
  • paper clips
  • ping pong balls (one per group)
  • pipe cleaners
  • scissors (1/student group)
  • straws, drinking
  • string
  • tape, masking
  • safety glasses


  • Collect an assortment of recycled and new materials that students will use to construct the prototypes. The materials list above is only a suggested list.
  • Determine the required quantities of materials for each working group and organize the materials.
  • Option: Provide students with a set amount of play money and set up a ‘store’ area where students can ‘buy’ their materials. This could be included in the design criteria (e.g., you must spend a minimum of $5 and a maximum of $10.).
  • Choose a large open area (such as the gym, or outdoors) for testing. Have students wear safety glasses.

What To Do

Students develop and apply Design & Build skills as they design, build and test a prototype ping pong launcher.

Stirling Warwolf Trebuchet model
Source: Ron L. Toms, Wikimedia Commons

Students will follow the steps of the Design & Build process:

  • identify the problem to be solved/need to be met
  • brainstorm criteria that the prototype must meet
  • share their questions and ideas for a solution to the problem/need
  • discuss the advantages and disadvantages of each in order to select a potential solution to be tested
  • visualize what the solution might look like and make design sketches based on their visualizations
  • develop a design plan (e.g., identify the tasks or key steps involved in developing the solution, make decisions about tools and materials that will be needed, include labelled sketches)
  • build/develop the design idea based on the design plan
  • test their prototypes based on the design criteria
  • modify the prototype and retest it against the design criteria as necessary
  • reflect on their results and identify things that could be done to improve their prototypes


Observe and document, using anecdotal comments, photos and/or video recordings, students' ability to:

  • Work Collaboratively –  students work collaboratively to complete a task and evaluate their group processes throughout the Design & Build process
  • Generate Ideas students use idea generation strategies, such as brainstorming, to identify possible solutions as well as make decisions about the pros and cons of each solution
  • Communicate students communicate their thinking and learning in words/sketches/photos/videos, etc. as they identify problems, do research, develop design plans, and share design solutions
  • Work Safely students demonstrate safe practices when using a variety of tools and materials while prototyping
  • Reflect students reflect on the results of their prototype testing and suggest things that they might do differently to improve their prototypes

Co-constructing Learning

Saying, Doing, Representing

Educator Interactions:
Responding, Challenging

Students identify and refine the problem to be solved/need to be met.

  • What do you know about ping pong balls and how they travel?”
  • What is the purpose of your device?”

Students brainstorm and record criteria for the ping pong ball launcher.

  • “What words could we use to describe some of the features the launcher must have to be effective?”
  • How will the force be applied to the ball?”

Students visualize what the solution might look like and make design sketches based on their visualizations.

  • “Why do engineers label all of the parts of their design sketches?”
  • “How are you going to represent each part of the launcher in the design sketch?”
  • “How will you make sure that the launcher is safe to use?”

Students make observations and decisions about the available tools and materials.

  • “What materials would be useful for building your launcher?”
  • “What tools might you need for building your launcher?”

Students build/develop and test the design idea based on their sketches and design plan (create the “prototype”).

  • “Is the launcher working as you expected? Why or why not?”
  • “What changes in your model might make the ball go higher/farther?”

Students modify the prototype and retest it against the design criteria as necessary.

  • “What problems did you have when you re-tested your launcher?”
  • “What changes in your launcher might make it more accurate?”
  • “How would it change your design if you wanted it to be easier to use?”

Students reflect on the results of their testing and identify things that could be done differently in the future.

  • “What materials worked best? What materials did not work as well?”
  • “What challenges did your team encounter in working collaboratively to complete the challenge?”
  • What would you do differently next time?”

Cross-Curricular Connections


  • Ask questions (e.g., “What surprised you about your device?” “What role did devices like these play in the past?” “What sorts of tasks could a device like this help us with?”)
  • Communicate thoughts, feelings and ideas (e.g., while brainstorming criteria for a launcher, in design plans that include 2D design sketches, in an outline of key design steps/tasks and lists of required materials and equipment/tools; discuss solutions for construction challenges)
  • Access information from various sources of media (e.g., books, videos, in-person experiences)

Mathematical Thinking

  • Represent using pictures, diagrams, graphs, tables, numbers, words, and/or symbols (e.g., sketch their visualization of how their launcher might meet the established criteria; use tables to record tests and redesigns of their launchers)
  • measure the distance travelled horizontally and/or vertically using both standard and non-standard measures

Extending the Learning

If your students are interested in learning more, the following may provoke their curiosity:

Ping pong ball, paddle and net
Source: megagepixelt, Pixabay

  • Encourage students to use the knowledge and skills developed in this challenge to solve a real-life problem, such as how to create:
    • an automatic ping pong ball launcher
    • a launcher that can get a ball to land on a ping pong table
    • a launcher that can have balls land in a bucket consistently
    • a launcher that can launch a toy for a dog to fetch 
  • Discuss with students how they would adapt the launcher to make it launch other objects such as tennis balls, basketballs, pumpkins, etc.
  • Provide opportunities for students to present their launchers before a mock “Dragon’s Den” panel (could be of teachers, older students and/or community members). The machines could be judged on originality, cost (if using play money), purpose (e.g., to launch a dog toy), accuracy, etc.