Catapult


 * Day 1: Design Brief**

In this unit you will be designing, building and improving a mechanical launching system resembling an ancient catapult. Your system will be scaled down and take advantage of elastic properties of modern materials. You will use both technological design and scientific inquiry as processes to investigate and improve how your catapult performs.

Design Challenge As a member of a product development team, you are to design, build, and document a mechanical launching system that can deliver a small object predictably and repeatedly over a specific range of distances (1 m, 3 m, and 5 m). You must have a trigger for the device.

Timeline Day 1 – Introduction Day 2 – Quick Build Research Day 3-4 – Investigation into Elasticity Day 5-6 – Building Periods Day 7-8 – Testing Day 9-10 – Writing the User Manual Day 11 – Competition Day

Log Book: Complete all of your work in a wikispace. That means you will write all notes, answer questions, draw designs, keep tables and graphs in this space. You may draw sketches by hand and then take pictures of them to upload to your wikispace. There should be daily entries reflecting the work you do each day. Each day should include both details of the work as well as pictures of the work you are doing.


 * Grading / Summary – Catapult**

Here is a list of what must be turned in and its point value. The total value of the project is 250 points.

Log Book (3 pts per entry) – This will be collected at the end of the project. The grade will reflect the amount of work completed as instructed. I will be looking to see the original record of your work. Each student will be asked to reflect on his or her contributions to the project relative to the rest of the group. Grades may be adjusted based upon this reflection. Be sure to include pictures of daily work.

Introduction – Answer questions in log book. Individual paper on history (10 pts)

Quick Build Research – Log book only

Investigation – Answer questions to consider in log book Individual paper (40 pts)

Building Phase – Log book only

Testing – Answer questions to consider in log book Group paper (40 pts)

User’s Manual (75 pts) Group Assignment

Group Reflection (10 pts) – Each member of the group should evaluate their contributions. Write a short synopsis of what you contributed and how the grade should be distributed.

Competition (20 pts) 1 pt for each time target is hit up to 15 pts – your group fires (15 shots) 1 pt for each time target is hit up to 5 pts – another group fires (15 shots)

History: Read the article on catapult design history. Write (typed) 2-3 paragraph summarizing key moments in the history of the catapult. You should find at least one website to use in addition to the article. Be sure to cite your online resources with the URL.
 * Day 1: History Research**


 * Day 2: Quick Build Research – Catapult**

The first step is to build a simple model catapult for launching a projectile. The time and materials will be limited. The idea is to build an experimental launcher and try it out to get a sense for what is important in designing and constructing the next catapult.

Put together your catapult and take it to the designated testing area. Your goal is to find ways to predict and control where the projectile goes. Each partner should participate in the launching as well as observing. All members should record observations and notes in your engineering log book.

Helpful Hints: • See if you can hit the target repeatedly • Find the minimum and maximum distance • Try elevating the catapult and try different launch angles • To gather your notes, identify what was happening, what did you change and what was the result. • Divide your observations into two categories: parts of the catapult (what you did to the catapult to make it work) and user operating procedures (what the operator might do to make it work) • Make a table listing the most significant variables and suggested modifications

What I already know about catapults:

Use a rubber band as a catapult and a pie plate as a target. Try to shoot a rubber band into the pie plate placed on the floor. Move the pie plate to different locations.

1. What important variables do you need to deal with as you try to hit the pie plate? Well, we need to find a way to launch the projectile using larger or smaller rubber bands to test the tension for each one. We also need to deal with angle of the base that the projectile sits on to get more height. 2. What scientific principles can you use to describe how your elastic catapult operates? 3. List any catapult-like devices of which you are aware (i.e. launching planes on aircraft carriers). 4. Define force and energy.


 * Day 3-4: Science Investigation**

The next step is to research the science behind your catapult. This step is taken to solidify the choices you will make for materials and design. A requirement of this catapult is that it must be an elastic launcher. For this reason, you will investigate the elasticity of materials. Please note that you may use any elastic material, but I am providing you with rubber bands to use for the experiment. Use your log book to record all work. You may paste graphs or pictures in.

Investigation: Study the relationship between force applied and the amount of stretch of a rubber band. All materials, even steel, have some stretchiness to them. The original theory behind elasticity was developed by Sir Robert Hooke (1635 – 1703) in his “Hypothesis of Springiness”. Today we know this as Hooke’s Law.

Research: Below are some websites which may be helpful. http://farside.ph.utexas.edu/teaching/301/lectures/node45.html - This is a background on the law. http://webphysics.davidson.edu/applets/animator4/demo_hook.html - An applet showing the graph of force versus elongation for a spring. http://www.phas.ucalgary.ca/physphotos/hooke.html - Just a picture. http://www.batesville.k12.in.us/physics/PHYNET/Mechanics/Newton3/Labs/SpringScale.html - This gives a procedure for springs.

Testing Hooke's Law:

Experimenting with Projectile Motion:


 * Day 5-6: Building Phase**

In this phase you will construct your catapult. The main rule is that the launching device must be elastic in nature. All plans must be sketched into your log book. The total cost of materials must be below $20. Donations are not acceptable. The idea is to create a prototype which could be manufactured on a large scale. If you use items that are not purchased, you must indicate the fair market value. Use a table (Excel is fine) to record the materials used and cost. Include receipts in your log book. Remember your device needs a trigger. Below is a list of materials you might consider:

Screws, nails, paper clips, binder clips, clamps, rivets, staples, bolts and nuts, hinges, wire string, elastic bands, clothespins, screw eyes, cup hooks, chain, pegs, slide / rail, clipboard.

Duct tape, masking tape, double sided tape, transparent tape, hot glue, super glue, rubber cement, contact cement, velco strips.


 * Day 7-8: Testing Phase**

Once your prototype is built, you need to test it for reliability. These tests will be included in your final report. Practicing with the device is also an important step towards writing the user manual. In this phase you will create a frequency distribution graph. This graph will be used to determine the distance for different force settings so you can set a scale on your device.

Links:

http://www.tufts.edu/%7Egdallal/prob.htm - Information on frequency graphs http://abacus.bates.edu/~ganderso/biology/resources/writing/HTWtablefigs.html - Information on presenting all types of data

General Procedure: 1. Launch a number of projectiles at a variety of force settings. Measure the distance the projectiles land. 2. The graph should be Successful Trials (y-axis) vs Distance (x-axis). You should use different symbols for the different force settings.

Questions to Consider: 1. What is the best feature of your catapult? 2. Describe the concerns you have at this point in the present design.

Write-Up: Your group should write a paper describing the approach your team took in designing and building the catapult. Include any problems encountered with the device or performance. Finally, include a summary of the testing of your device.


 * Day 9-10: User’s Manual**

The final activity is for you to communicate the results of your work in a User’s Manual. You should include information that would interest others about using your catapult and its capabilities. Your writing should communicate clearly. It needs to be well organized and clear enough for someone unfamiliar with your team’s catapult to understand.

Below are the parts to include:

CATAPULT USER’S MANUAL Table of Contents System Overview – includes a sketch Parts and Materials Specifications – size, shape, composition, and quality of parts Performance Specifications – describe capabilities of catapult, min and max, accuracy Operating Instructions – step by step Safety Measures Firing Tips – advice including “do’s and don’ts” Launching Graph Science of Catapult Appendices
 * Similar Product Comparisons – identify strengths and weaknesses
 * Preventive Maintenance – how to keep it going
 * Repair and re-calibration – how to fix it
 * Disclaimers and Warranty – what should you be responsible for?


 * Day 11: Competition Day**

Reflection

Reviewing your work and seeing what you learned are important steps in completing the design process. In this assignment you will reflect upon your work. The questions are below but you will respond in Blackboard.

What went right and wrong in your work. Take a few minutes to think about what worked and did not work for your catapult design. What would you do differently? Respond to this with a posting.

The design process Look back at the design process given in class. What steps did your group use? Which steps did you not use? Are the steps helpful in completing your work? Explain

Feedback You will be in charge of another group’s catapult testing by the general science class. Report how the testing went in general. Give any advice to the designers you may have found. After the designers read this feedback, you should respond with comments (school appropriate of course).
 * Day 12 - General Science Testing**


 * Day 13 - Wrap-up and Conclusion**

Self Evaluation Evaluate your role within the group. How much did you contribute? How much did your partners contribute? How should the grade be divided / assigned? Was it difficult to work in a group? Write your answers to this and submit it to the digital dropbox under the Tools section of Blackboard.