Backyard Engineers Teacher Guide - Design Your Own Catapult

Design Your Own Catapult

Time Required



Students will show what they know about forces, motion, work, and machines by designing and testing their own catapults.



Wooden craft sticksMasking tapeRubber bandsScissorsPencilMetric rulerMiniature marshmallowsCatapult Scoring Rubric


Computer and Internet access


Gather materials for each student to complete the engineering activity.

Warm Up: Exit Slip Discussion

Distribute (or provide access to) students’ Exit Slip responses from Lesson 3 and review the responses as a class.


Have students continue their last Backyard Engineers game with their partners for approximately 30 minutes. However, if enough computers are available, students can start a new game and play individually.

  • Allow students to play uninterrupted, but ask them to think about how they might build their own catapults to launch marshmallows.
  • Encourage students to think about the materials they could use.

Engineering Activity

Instruct students to read the description of the engineering activity in the Student Guide. Distribute the materials, and use your own discretion in making sure students know the rules about eating and launching the marshmallows. Review the three main stages of the engineering process:

  • Define a problem: identify the criteria and constraints of a task. The criteria refer to the requirements necessary for the task to be completed using the design. The constraints refer to limitations on the design due to the available resources and the environment.
  • Develop solutions: develop, test, and modify a design that is meant to solve the problem.
  • Optimize the design solution: choose the design with the optimal advantages in order to solve the problem.

Let students know that they can use the materials provided to build a catapult in any way they like, but the catapult must be capable of converting potential energy into kinetic energy in order to do work, or launch a marshmallow. Review the scoring rubric, and then have students begin by asking them to sketch their designs. As part of the design process, be sure that students focus on identifying the criteria and constraints. What is required of the catapult in order for it to work? What are the limitations of the design? Have students record their answers on the Design Your Own Catapult Sheet, and check their responses when you review and approve their designs.

Once you approve their designs, students can start building and testing their catapults.

If time allows, hold a class-wide competition using the catapults. Start by forming small groups of 3 or 4 students. Groups should set up a target and see who is the most accurate and precise at hitting the bullseye after three tries. The winner from each round moves on until the most accurate marshmallow launcher is found!