Catapults and Trebuchets

Facilitator Guide 4th-5th Grade Curriculum

AFTER SCHOOL STEM ACADEMY

Questions about the curriculum?Please contact April Nilsen at Washington Alliance for Better Schools: april@wabsalliance.org (206) 393-4506

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CatapultsandTrebuchets

WABSAFTERSCHOOLSTEMACADEMYSpring2017

OVERVIEWOver the course of the first three sessions, students will build small-scale catapults and test them based on various criteria. Then, they will design and build a larger trebuchet, explore concepts of load and balance point. In the final lesson, students will test their designs across all three criteria – accuracy, power, and knocking down a tower. Lesson 1 – What is a Catapult? Lesson 2 – Go the Distance: Testing Power Lesson 3 – Right on Target: Testing for Accuracy Lesson 4 – Assembling a Trebuchet Lesson 5 – Finding the Best Load Lesson 6 – Trebuchet Olympics

CATAPULTVS.TREBUCHETA catapult is any device that throws an object, although it commonly refers to the medieval weapon. Trebuchets are a type of catapult, using gravity (with a counterweight) or traction (people pulling down), to propel the arm and often employing a sling at the end of the arm for greater distance.

VOCABULARY Accuracy: The ability to hit the target.

Catapult: A machine that launches a projectile.

Projectile: An object that is launched or thrown, usually in the air, by a force.

Quadrilateral: A polygon with four sides. Examples include squares, rectangles, and trapezoids.

Triangle: A polygon with three sides.

Torque: A twisting force that tends to cause rotation.

Force: The push or pull on an object.

Fulcrum: The support about which a lever pivots.

Load: A weight or source of pressure.

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TEACHINGNOTES

CompetitionThere is a natural tendency for this project to turn into a competition – everyone wants to have the trebuchet that shoots the farthest. Although this can be highly motivating for students, the situation needs to be continually monitored so that the students are not putting each other’s efforts down by overemphasizing the competitive aspect. Remind students that although scientists, engineers, and designers do compete, they more often work together to find the answers to a problem. The goal in this session is for the whole group to learn from each other about what works and what doesn’t when designing and constructing catapults & trebuchets.

BrainstormingWhen you are leading a brainstorming session or reflection, make sure to preface it with the most important rule: No one may make a judgment about someone’s idea. This will help students remain positive and open to sharing. If you are unclear on what a student is trying to say, ask open-ended questions like, “Tell me more about …” or “Say more about…”.

PacingSome students may be able to put together a catapult or trebuchet rather quickly. The challenge is to refine each design and discover the principals of its use. Therefore, try to motivate students to continue working beyond their initial success so that they take the time to troubleshoot and test their designs. Discussion and collaboration are integral parts of the design process in every lesson – it is likely that the classroom will get loud! However, you can help groups refocus if it seems like they are just chatting, or only talking about non-relevant topics. It is helpful to give notices when there are 30, 15 and 10 minutes left in each session so groups can pace themselves.

SafetyEach lesson will involve some type of “launching”. While the materials being launched are all lightweight, safety precautions should still be taken. Students should only launch the projectile indicated in each lesson – cotton ball, marshmallow, ping-pong ball, or paper “cannonball”. Some students may be tempted to launch other items – such as small toys or other hard objects. This needs to be immediately shutdown, as it is not safe. Set clear rules about launching based on the space you are in. You may ask students to launch in the hall if that is an accessible space. You could also do some testing outside weather and space permitting; if you do this, ensure that all projectiles and debris are cleaned up after testing is complete. Some sample rules:

1. Launch only the cotton ball [or other projectile, depending on the lesson]. 2. Aim your catapult [or trebuchet] away from people. 3. Do not launch your projectile by hitting your catapult [or trebuchet].

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LessonOne

WhatisaCatapult?

INTRODUCTIONOver the course of the next 6 weeks, we will be learning about, designing, and testing different types of catapults.

Before we can dig in to our first activity, we need to talk about what a catapult is!

Ask: Can anyone tell me what you know about catapults? (Accept all answers)

Ask: Has anyone heard of a trebuchet?

Go over the definition below:

CATAPULTVS.TREBUCHETA catapult is any device that throws an object, although it commonly refers to the medieval weapon. Trebuchets are a type of catapult, using gravity (with a counterweight) or traction (people pulling down), to propel the arm and often employing a sling at the end of the arm for greater distance.

Say: Given this definition, we will be working on catapults all 6 weeks, but will focus specifically on trebuchets the last 3 weeks.

TODAY’SCHALLENGEYour challenge today will be to use some everyday materials to create catapults that can launch ping-pong balls. The catapult you design must be able to knock down a tower made of plastic cups.

MATERIALS

• Cardboard • Masking tape • Plastic spoon • Rubber bands

• Craft sticks • Straws • Ping-pong ball • Plastic cups (for the tower)

PROCEDURE1. Discuss the Engineering Design Process. Display the poster, either on the board or under the

doc cam. We will revisit this process each session. • Whenever engineers are faced with a challenge, similar to the one we've just discussed, they

use a tool called the engineering design process to help them come up with good solutions. The first step in this process is to ask what the problem or challenge is. For us, that's easy—we need to develop a machine that can launch Ping-Pong balls.

• The next step is to imagine ideas. You can imagine in many ways, but a common method is to brainstorm, draw and discuss ideas as a team.

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• After brainstorming, the best one or two ideas are chosen and formed into an initial design, or plan. These designs are drawn on paper, with all individual parts labeled and a list of necessary materials.

• Once this design is complete, materials are gathered and the team will create a their design. • Unforeseen problems are almost always discovered - even by engineers who have been

designing for 20 or 30 years! Don’t expect your catapult to work perfectly the first time – the improve step is key to making the best design possible. The point is to learn from your mistakes, make changes to the design, and perform lots of tests.

2. Divide students into groups of 3-4. 3. Groups brainstorm ideas for their catapult. Individuals and groups draw designs in their

engineering notebook, including a materials list. 4. Groups collect materials (except ping-pong balls and cups). 5. Groups build their design. 6. Facilitator should set up the testing zone. Build a tower from 6 plastic cups. Indicate the “start

line” using masking tape so all catapults are tested from the same distance. 7. Groups test their design with a ping-pong ball. Each group should have approximately 5 attempts

to successfully knock down the cup tower. a. Groups record their test results.

8. Groups discuss what worked and what didn’t in their design. They then redesign their catapult and test again, as time allows.

REFLECTIONMake sure that 10 minutes before the session is over, students clean up the materials. As a class, discuss the following questions:

1. What worked well in your catapult design? 2. What aspects did you have to modify? 3. Were you able to knock down the cup tower? How many times? 4. What would you do differently next time?

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LessonTwo

GotheDistance:TestingPower

INTRODUCTIONLast week, you built a catapult and tested it by seeing if you could use it to knock down a cup tower. This week, you will be designing a catapult that you think will be able to send an object (mini-marshmallow) the farthest distance.

TODAY’SCHALLENGEBuild a catapult that can launch a mini-marshmallow the longest distance.

MATERIALS• Cardboard • Masking tape • Plastic spoon • Rubber bands • Craft sticks • Straws

• Paper bowls • Plastic lids • Small paper cups • Mini-marshmallows (for testing) • Measuring tape (for testing)

PROCEDURE1. Divide students into groups of 3-4. 2. Groups brainstorm ideas for their catapult. Individuals and groups draw designs in their

engineering notebook, including a materials list. 3. Groups collect materials. 4. Groups build their design. 5. Facilitator should set up the testing zone. The testing zone should have a starting line (masking

tape). If time/space permits, it is helpful to mark certain distances (ex. 5 feet, 10 feet, etc.) with masking tape.

6. Groups test their design with a marshmallow. Each group should have 3 attempts to launch the marshmallow as far as possible. Use the tape measure and record the distances.

a. Groups record their test results. 7. Groups discuss what worked and what didn’t in their design. They then redesign their catapult

and test again, as time allows.

REFLECTIONMake sure that 10 minutes before the session is over, students clean up the materials. As a class, discuss the following questions:

1. What worked well in your catapult design? 2. What aspects did you have to modify? 3. How far was each team able to launch a mini-marshmallow? 4. What do you think helped launch the marshmallow farther?

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LessonThree

RightonTarget:TestingforAccuracy

INTRODUCTIONLast week, you built a catapult and tested it to see how far you could launch a mini-marshmallow. This week, you will be designing a catapult that you think will be able to launch an object with the greatest accuracy.

TODAY’SCHALLENGEBuild a catapult that can launch a cotton ball accurately. In this activity, accuracy is the ability to get the cotton ball into the bowl.

MATERIALS• Cardboard • Masking tape • Plastic spoon • Rubber bands • Craft sticks

• Straws • Paper bowls • Plastic lids • Small paper cups • Cotton ball (for testing)

PROCEDURE

1. Discuss the principals relevant to today’s design challenge. To propel the ping-pong ball long distances, significant forces will be applied to the structure of your catapult in many different directions. Let's talk a little bit about force, or the push or pull on an object. If the launching part of your catapult is held with a lot of force, your projectile (the cotton ball) will also be launched with a lot of force.

a. If your cotton ball is not making it to the target, should you increase the force on the launcher or decrease it? (Answer: Increase.)

b. What if you launch your cotton ball and it goes way past all the targets? Should you increase or decrease the force on the launcher for the next trial? (Answer: Decrease.)

c. To make sure that your structure can withstand all of these varying forces, there are certain shapes that are stronger than others. What do you think would be stronger: a triangle or a rectangle? (Answer: Triangle.)

d. A triangle is the strongest geometric shape because its sides cannot move unless their lengths change. This means that if you make a triangle using popsicle sticks, one of the popsicle sticks would have to break in order for the shape to change. On the flip side, a square or a rectangle can easily compress and change shape into a diamond or other type of quadrilateral without any of the sides changing length. These shifting shapes could lead to a lot of stress on the joints and might cause your catapult to collapse as you try to launch a cotton ball. Consider using lots of triangles in the frame of your catapult.

2. Divide students into groups of 3-4.

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3. Groups brainstorm ideas for their catapult. Individuals and groups draw designs in their engineering notebook, including a materials list.

4. Groups collect materials. 5. Groups build their design. 6. Facilitator should set up the testing zone: set up the bowl, and mark the “starting line”

approximately 3 feet back from the bowl. Feel free to adjust based on what you observe with your group.

7. Groups test their design with a cotton ball. Each group should have 5 attempts at a time to successfully get their cotton ball into the bowl.

8. Groups record their test results. 9. Groups discuss what worked and what didn’t in their design. They then redesign their catapult

and test again, as time allows.

Optional Extension: If groups finish early or would like an additional challenge, post a target, with concentric circles. The center circle is labeled 200, next 100, next 50, and finally 10.

We will use our catapults to play a game in which we aim and fire our catapults, trying to hit different targets. Hitting the targets earns you different amounts of points: 10, 50, 100 and 200. We want our catapults to be accurate in order to hit the maximum number of targets. In addition to making accurate catapults, we also want to make sure that our catapults shoot the cotton balls far enough to hit the targets.

REFLECTIONMake sure that 10 minutes before the session is over, students clean up the materials. As a class, discuss the following questions:

1. What worked well in your catapult design? 2. What aspects did you have to modify? 3. How accurate was the catapult that your team designed? 4. What would you do differently next time?

Adapted from: https://www.teachengineering.org/activities/view/cub_catapult_lesson01_activity1

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LessonFour

AssemblingaTrebuchet

INTRODUCTIONLast week, you built a catapult and tested it to see how accurately you could launch a cotton ball. This week, you will be building a trebuchet that you will use over the final three lessons.

TODAY’SCHALLENGEBuild a trebuchet and make it work.

MATERIALS• Empty water bottles • Rulers • Ruler • Wooden dowels (20-inch) • Wooden dowels (4-inch) • Paper cup (6-9oz)

• Washers • Rubber bands • Binder clips • Masking tape • Paper bowls • Paper

PROCEDURE Have students turn to the trebuchet model in their student journal. Ask, What do you notice about this machine? Probe for comments on its size, design, materials, history, and how it was used. As students how you think the machine works, and what it was used for. Note that the trebuchet was invented over 1,000 years ago – it was used in Europe, China, and the Middle East to attack stone castles or ships. Ask students to look at the figure of the trebuchet in their student journal. Notice all the parts and how they fit together. Use the picture and the instructions in your journal to build your own trebuchet with your teammates. (Note: there is a detailed diagram on the following page in case students need additional assistance. However, allow students to experiment with their own designs before showing them this diagram.)

1. The ruler will be your throwing arm. Attach the ruler to the dowel using a rubber band. This makes the fulcrum (balance point) of the throwing arm.

2. Slide the dowel up or down the ruler so that the fulcrum is at the 4-inch mark. 3. Use a load of 10 washers and attach it to the short end of the throwing arm. 4. Cut the top off the paper cup so it is about 2 inches deep. Fix it to the top end of the throwing

arm to hold a cannonball. 5. Fill the water bottles and screw the lid on tightly – they bottles need weight in order to form a

sturdy base for the trebuchet. 6. Make a cannonball out of a single sheet of paper and tape. See how far you can launch it!

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Trebuchet Diagram: Allow students to experiment with their own designs – avoid showing them this diagram

Note: You will be using water bottles instead of gallon jugs, and a ruler instead of yardsticks. This will change the dimensions of the trebuchet to make it slightly smaller, but the concepts remain the same.

Paper cup base

Ruler

Wrap around water bottles

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TROUBLESHOOTING

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DESIGNPROBLEMS:MAKINGITSHOOTSTRAIGHT Even though the throwing arms may swing very nicely, a number of other factors need to be just right if the cannonball is to launch in the right way. Common problems are that the throwing arm slides out of position, the cannonball falls out of the cup at the back of the swing, or (the opposite problem) it “slam dunks” into the floor right in front of the trebuchet, meaning that it holds onto the cannonball too long. Ask students for their ideas on how to solve these problems before you give them the hints below:

Adapted from: Trebuchets: Design It! Engineering in After School Programs

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REFLECTION With about 10 minutes left in the session, have students clean up and come together to discuss what they have done today. Have each team briefly present their trebuchet, identifying what worked well, and what they would like to improve for next time. Ask some follow-up questions:

1. Do the water bottles need to be the same height? What happens if they are not? 2. How can you make sure the throwing arm is swinging freely? 3. What was the best way you found to attach the throwing cup?

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LessonFive

FindingtheBestLoad

INTRODUCTIONLast week you built your trebuchet and troubleshooted to make sure it was working well. This week, it is time to find out how to control the trebuchet’s range, or how far the cannonball flies. What changes can you make to your trebuchet so it will shoot the cannonball farther?

TODAY’SCHALLENGEFind the best amount of load (number of washers) to shoot the cannonball the farthest.

MATERIALS• Trebuchets from Lesson Four • Additional washers • 4-inch dowels • Rubber bands • Binder clips

PROCEDURE1. Let the students know that the challenge for today is to work with the trebuchet they built last

week to try to shoot the cannonball farthest. Ask: What do you think might work to modify the trebuchet to make the cannonball shoot farther or less far? Have students brainstorm ideas.

a. Many students may think that changing the weight on the throwing arm may make a difference. If this idea does not come up, suggest it and see what the students think about it.

2. Once the students have finished brainstorming, make today’s challenge more specific by stating: Today’s challenge is to find the best amount of load (number of washers) to shoot the cannonball the farthest.

3. Divide into the small groups that worked together last week. Check in with groups and make sure that they all have roles and understand the challenge.

4. Check that the throwing arm is set at its home position on the fulcrum – 4 inches from the tip of the ruler.

5. Make a stack of 5 washers and fix this new load to the trebuchet. Test the trebuchet 2 times – record how far the cannonball goes.

6. Add more washers and continue to record your results and the number of washers used to find the optimal, or best, load.

REFLECTION1. What did you notice about the change in load for your trebuchet? 2. What was the farthest distance any group was able to launch the cannonball? 3. Why do you think you had to test each load more than once?

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LessonSix

TrebuchetOlympics

INTRODUCTIONOver the last two weeks, you have built and modified a trebuchet. Today, you will use it to complete three tests – accuracy, power, and ability to knock down a tower. You will present your trebuchet to the class at the end of the session.

TODAY’SCHALLENGEUse your trebuchet to compete three tests – accuracy, power, and ability to knock down a tower.

MATERIALS• Trebuchets from Lesson Five • Cotton balls • Paper bowl • Ping-pong ball • Plastic cups

• Masking tape • Mini-marshmallows • Measuring tape • Olympic Passport (one per group for

recording results)

PROCEDURE Set up the three testing stations as follows:

1. Accuracy a. Set up a paper bowl, and mark the “starting line” approximately 5 feet back from the

bowl. Feel free to adjust the starting line based on what you have observed about the trebuchets (i.e. the starting line may need to be further back).

b. Each group should have 5 attempts at a time to successfully get their cotton ball into the paper bowl.

c. Groups record the number of times they are able to get the cotton ball into the paper bowl on their Olympic Passport.

2. Power a. Mark a starting line with masking tape. If space permits, it is helpful to mark certain

distances (ex. 5 feet, 10 feet, etc.) with masking tape. b. Groups should have 5 attempts to launch a marshmallow as far as possible. c. Groups record the distances they launch the marshmallow on their Olympic Passport.

3. Tower Topple d. Build a tower from 6 plastic cups. Indicate the “start line” using masking tape so all

catapults are tested from the same distance. e. Groups test their design with a ping-pong ball. Each group should have 5 attempts to

successfully knock down the cup tower. f. Groups record the number of times they are able to knock the tower down on their

Olympic Passport.

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REFLECTION1. In which event was your trebuchet most successful? Why do you think that was? 2. Which event was most challenging? What do you think you could have done to make it easier? 3. Think back to all the catapults and trebuchets that you have made over the six weeks. What do

you think was your best design and why? 4. What do you want to design next?