Crazy Creative Catapults

A) Objective: To introduce students to the concepts of projectile motion, fulcrums, and the elastic properties of different materials.

B) Time: 45 min for building and initial explanation, 15 min for testing. Total: one hour.

C) Materials:

• List of Materials:
  1. A maximum of 7 popsicle sticks per group
  2. 5 elastic bands per group
  3. Masking tape for each group
  4. 1 pie plate per group
  5. 2 sheets of scrap paper per group
• Materials found at: dollar stores, stationary supply, can be donated
• Cost per student: $0.30
  

D) Theory:

1. Projectile motion: the greatest distance can be achieved when the machine can release the object at a 45° angle (depending on the design). The students must consider how to make their machine so it shoots across to maximize distance as opposed to straight up or straight across.
2. Material properties: all properties used in this demonstration exhibit some elastic properties. These materials can be used in different combinations to launch a projectile.
   • Elastic properties of a popsickle stick can be demonstrated by pulling it back and slapping it on a desk or even an arm (if someone is skeptical!).
   • An elastic band doesn't have much energy if it's just tossed at someone, but if it's pulled back...ouch! (tell the kids if they try this, the elastics will be taken away). So they'll have to think of a way to put energy into their machine by tightening the elastics.
   • Paper even has elastic energy if it's scrunched up!
3. Some kids will design a "seesaw" design which uses a fulcrum:
   Example: put one person on a seesaw and they are sitting on the ground. What happens if you drop a one tonne weight on the opposite side?

E) Procedure:

1. The materials should be distributed to each group.
2. The goal of the building project is to create a catapult that will launch the designated object (e.g. an eraser) the furthest.
   • The students will be free to build in whatever way they think best, but the instructors should circulate to ensure a degree of success for each group. Encourage different types of designs...seesaws are good for younger kids because they are easy to build and fire. Slingshots don't work as well. The "traditional" catapult design works very well but is more difficult to conceive and build.
   • An optimal angle of takeoff is important as well as the amount of stored elastic potential energy.
3. The first half hour to 45 minutes of the project will be spent building and the last 15 minutes will be spent testing and launching the catapults.
4. A target board will be built with different areas, the goal being to reach the farthest area to become a Super Cool Science Geek. Other areas closer to the launching site could be Einstein's, Newton's, Curie's or any other famous scientist. The closest could be named for a science student.
   

F) Safety: Watch out for flying objects during the testing phase of this project! Set strict guidelines regarding the elastic bands for use other than building.