# Mini Siege Engines

Ah catapults - possibly the most engaging and exciting project to introduce students to some fundamental ideas in physics and engineering. Stored energy, trajectory, the value of density in projectiles, and of course firing stuff across the room - so much to learn, and yet so much fun to be had!

Learning Objective
Students will...
• Use a hands-on approach to explore and comprehend basic concepts in engineering and physics like stored energy, trajectory, reinforcement, density, levers and hinges, and trusses.
• Acquire an understanding of the different parts of a catapult: the base, the support structure, the arm, and the basket.
• Strengthen critical thinking and motor skills as they build their siege engines and troubleshoot any design flaws that may arise.
Materials: Craft sticks, craft cubes, cubes with holes, rubberbands, skewers (less than 1/8" diameter), corks, plastic cups, paper, tape, and hot glue.

Lesson plan

Difficulty: 3/5
Prep work: 2/5
Setup time: 2/5
Cleanup: 2/5

Each mini siege engine is built differently, so I will outline how to build the individual models in the following steps. For now, let's focus on what these little war machines have in common:

Trusses: I explain to the students what a truss is and why it's so strong and useful. Trusses are basically triangles that are used to strengthen a structure. Trusses do not change their shape easily, unlike squares which can flatten into rhombuses (sometimes I will make a triangle and a square out of craft sticks and show the students how easy it is to squash a square, but not a triangle). Trusses also require very little materials which makes them highly efficient. The catapult in the photo above uses trusses to support the downward pull of the catapult arm. If the trusses were replaced with a pair of beams perpendicular to the base, the whole support structure would collapse if the arm were to be pulled down.
Reinforce: This is easy to explain - reinforce simply means adding more material to make something stronger, like gluing sticks on all sides of the base instead of just one.
Trajectory: I explain that trajectory is the path that an object, or projectile follows through the air. What happens when the projectile is aimed upward at 45 degrees? The trajectory it takes will be a nice smooth arc. Aimed straight forward? Immediately begins to fall toward the ground. ( Just like in Angry Birds - kids can really relate to this!) Changing the trajectory will change how the projectile moves. Most kids understand this intuitively.
Remove these ads by Signing Up

## Step 1: Simple Catapult

This catapult is a very easy project to teach! I have had groups of children in grades 1-5 make this. The finished catapult feels very study and it can fire up to 30' from a tabletop.

The easiest way to show kids how to build this is by taking the the catapult apart into it's two components: the base + support, and the catapult arm. Point out the key features of the design like where the hinge will be, how the cubes with hinges are not connected with sticks, and how the cubes on the base are connected on three sides to make the base sturdy. Next, show the students how to assemble the catapult and attach the rubberbands - students in grades 1-3 typically need help with this.

Pulling on the catapult arm stores energy in the rubberbands. When the arm is released, the stored energy is transferred into pulling the arm rapidly upward and into the crossbar. The catapult arm stops upon contact with the crossbar, but now the projectile still has momentum and will continue to follow its trajectory.

To fire:
• Firmly hold down the front of the catapult
• Pinch the cube under the basket and pull down, then release
kevmcd says: May 19, 2013. 3:14 PM
Quite simply splendid!
PoisonDartFrog says: Mar 29, 2013. 11:41 AM
To get corks, do you just save them from bottles or do you by them en masse from somewhere?
yapoyo says: Sep 7, 2012. 4:22 PM
I like this very much. How can I make this without the craft cubes? Are they really necessary?

WYE_Lance (author) in reply to yapoyoSep 7, 2012. 6:13 PM
The cubes aren't necessary - I use them because it's what I use in all of my projects. I don't know what you have access to, so if I were you I'd rummage around my home for materials or visit a craft or hardware store. Good luck!
ynze says: Jun 21, 2012. 1:26 AM
And again congrats for being a winner in the Education Contest! Great project!
WYE_Lance (author) in reply to ynzeJun 21, 2012. 1:06 PM
Thanks! I am so psyched!!
poofrabbit says: May 25, 2012. 12:09 AM
Congratulations on being a winner in the Big and Small contest!
WYE_Lance (author) in reply to poofrabbitMay 25, 2012. 7:19 AM
Why thank you - you're quite gracious. I've seen your positive feedback all over the site. Keep it up, and good luck in future contests :)
poofrabbit in reply to WYE_LanceMay 25, 2012. 6:08 PM
Awe you are so kind! I was excited to read you are in talks with instructables to sell a kit of one or more of your instructables! I think that is wonderful!! Your partner in education, poofrabbit
person% says: May 25, 2012. 1:14 AM
nice!

i used to enjoy making shooting thingies, i once made a thing similar to the skewer shooter, but it was aluminum (from cans) and it used a thick red rubber band and it can shoot sticks and pencils as well, but it wasn't as strong. i used to sell them as well. they don't reload very quickly and is not very accurate, so i use it close range. i also made a lot of similar shooters, one of then is a sliding one for extra power, and one that is about 2-3 centimetres long for hiding it from teachers.

i still think that the ones i just said do too much damage and gets me into a lot of trouble, so now i making paper wasp shooters.
rimar2000 says: May 1, 2012. 2:09 PM
Very fun for kids!
snoo says: May 1, 2012. 5:34 AM
this will be great for food fights!!!!!!!
batonas says: Apr 30, 2012. 12:39 PM
I love all your project, they are simple, afordable for anyone and great for children physic education, way more fun than reading a boreing book.
Keep up the good work.
P.S. you could sell diy sets for these project I think people would be glad to buy it.
WYE_Lance (author) in reply to batonasApr 30, 2012. 6:20 PM
Wow, thanks for the kind words :) I've been talking with the Instructables HQ about selling the rubberband helicopters as kits - hopefully we'll see them in the store soon!