Catapult

Author: Future Scientists and Engineers of America (FSEA). Adapted by

CCMR Date Created: 1997 & Adapted in 2014

Subject: Engineering, Physics Level: 4th grade to 8th grade Standards: Next Generation Science Standards (www.nextgenscience.org)

3-PS2-1 Plan and conduct an investigation to provide evidence of the effects of balanced and unbalanced forces on the motion of an object. 4-PS-3-4 Apply scientific ideas to design, test, and refine a device that converts energy from one form to another. MS-PS3-1 Construct, use, and present arguments to support the claim that when the kinetic energy of an object changes, energy is transferred to or from the object. MS-ETS1-4 Develop or model to generate data for iterative testing and modification of a proposed object, tool, or process such that an optimal design can be achieved. Schedule: Two or three 45-minute class periods

Objectives:

Give students an experience in engineering while teaching principles of physics. Introduce students to the scientific processes of experimentation and trial and error.

Students will:

• Be introduced to the history of catapults and the theory of how they work.

• Learn physics vocabulary terms.

• Assemble a basic catapult from the materials provided for them.

• Observe the changes in the catapult’s performance after adjustments.

• Record their catapult’s performance.

• Compete to test their team catapult’s accuracy at hitting targets at various distances.

Vocabulary:

Potential Energy Kinetic Energy Work Lever Fulcrum

Force Variable Dependent Variable Independent Variable

Materials: For Class: Glue gun Catapult Kit:

4 Rubber bands, Pushpin, 2 Nuts (1/4 x 20), 2 Machine Screws (1/4 x 20 x 4 1/2”), 4 Drywall Screws, 4 Screw Eyes (Open Eye), Hook & Chain, Wood Arm and Base, 2 Pegboard Sides, Whiffle ball Target

For Each Student: Catapult Materials: 4 Rubber bands, 12 Popsicle sticks Paper cup Spoon

Activity Sheet 1:

Catapult Variables Activity Sheet 2:

Appendix B Activity Sheet 3:

Catapult Science Challenge Questions

Safety: Be sure students are shown how to properly use the glue gun.

Science Content:

Over 2000 years ago, the Greeks and Romans did not know about gunpowder, yet were able to hurl projectiles over a large distance using kinetic energy storage devices. Through the years, some modifications were made to increase the accuracy and throwing distance of these machines. The first two types of throwing machines were the catapult and the ballista. The catapult started out as a large cross bow to shoot oversized arrows at an enemy. The ballista was about 10 times larger than a catapult and threw large stones.

The ballista’s design consists of two pieces of wood, each fastened at one end to a torsion device rotating about a more or less horizontal axis. The free ends of the wooden pieces are connected together with a rope. The projectile to be thrown is held by the connecting rope used as a sling.

When most people think of the catapult, they are actually thinking about an onager. The strange name is derived from a wild donkey kicking with its hind legs. The onager (or gone, mangonel, or nag) was typically a single spar held in a more or less vertical position by a torsion device rotating around a horizontal axis. The projectile was located in either a pocket at the top end of the spar or in an attached sling.

The choice of the Middle Ages was a trebuchet. This device used gravity instead of torsion springs to provide propulsion energy. The theory is simple: put a large weight at the short end of a lever arm and put the projectile in some kind of basket at the other end of the lever. The velocity of the projectile can become quite large when the ratio of the lengths of the lever arms is great. Incidentally, the trebuchet was also used as a punishment device called the ducking stool. People were placed in a seat at the long end and successively ducked into a pool of water.

The catapult is still in use today, although radically different from those used in history. The modern catapult is used to launch aircraft from the deck of an aircraft carrier. The aircraft carrier catapult uses steam as a source of energy to push a piston along a linear track in the aircraft carrier’s deck. The piston pushes the aircraft and accelerates the plane up to flying speed in a very short distance. The same kind of mechanism can be found at Knott’s Berry Farm, where it propels the Montezuma’s Revenge roller coaster ride.

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The following information is for the mentor/teacher to build a model catapult to demonstrate to the class. You can build this before the class or with them.

Assembly Instructions

1. Align the sides with the base and screw in the drywall screws to secure it.

These are represented by the x’s in the below picture. Be sure to have the pre-made holes on the bas facing up.

2. Insert the machine screw through one of the top holes of one side,

followed by a spacer, the lever arm, another spacer, and then the corresponding hole on the second side. Secure this with a nut, making sure to leave it just loose enough for the arm to swing freely. Be sure to have the pre-made holes on the lever arm facing down.

3. Now install the second bolt as a stop for the arm. Make sure it is below

the bolt holding the lever arm (fulcrum) and closer to the front. You need not make it terribly tight.

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4. Install the hooks at both ends of the base.

5. Install a hook at the front end of the lever arm, and a screw eye at the rear

end.

6. Install the hardware in appropriate location (variable). The length of chain

with the gate-hook and attached string which acts as a trigger device should always be mounted on the catapult base, with the separate gate- hook eye ONLY being mounted on the catapult arm as shown above. At no time should the jack-chain with the gate-hook attached be flying through the air in an arc at the end of the catapult arm each time the catapult is triggered.

7. Install cup on the lever arm (used to hold the whiffle ball).

8. Install rubber bands.

9. Test catapult and discuss how it works. Identify and test out different

variables.

10. Give students materials and have them design, build, and test their own

catapult.

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Preparation:

1. Photocopy print materials (Activity Sheets 1-3) for each student. 2. Students should conduct some library research on the subjects of catapult, trebuchet, and onager before beginning this assignment. 3. Distribute materials evenly to each student pair. 4. Construct target range (see Supplemental Information below).

Classroom Procedure:

Before Class (15 mins)

Have students watch a video on mechanical energy: https://www.youtube.com/watch?v=8hrFBYp5LYs#t=15

Have students go to site and find out about the 3 classes of levers: http://www.enchantedlearning.com/physics/machines/Levers.shtml

Engage (Time: 20 mins)

Discuss the history and types of catapults outlined in “Science Content” with the students. Discuss potential and kinetic energy. Introduce levers and discuss the 3 classes of levers. Demonstrate a working catapult to the class. Ask the students to engage in a discussion on what variables they can apply to the catapult to vary the distance to which it can throw a projectile. Discuss the adjustments and how they would affect performance. Test out some of the adjustments.

Explore (Time: Varies)

Provide each student with their materials. They will need to design and build a working catapult capable of lobbing mini marshmallows at a target. Inform students that there will be a competition to test their catapult’s accuracy at hitting targets at various distances. They are given a basic design to build. Encourage students to discuss the physics principles and vocabulary they learned as they construct their catapult to increase their understanding.

Set up the target range in the classroom for the competition. Have students test and collect data on the distance the catapult is moved back (potential energy) and the distance the marshmallow travels (kinetic energy). Have them create a line graph showing this relationship. Distribute marshmallows to each student. Tell them they will use these to test their catapults and let them practice hitting the targets. If need be, allow them to adjust the variables on their catapult. Next, discuss the scoring system for the competition (refer to Appendix A3). Explain

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how teams should take data on their own performance (refer to Appendix A4, Scoring Sheet, and Longest Distance sheet) and let the competition begin!

Explain (Time: 10 mins)

Discuss with students what did and did not work, have them explain why certain settings worked better than others. Distribute Activity Sheet 3: Catapult Science Challenge Questions as a homework assignment to each student. Allow the students to work on it with a partner. During the next class period, discuss the challenge questions and clear up any misunderstandings the students may have about the concepts they learned.

Assessment:

The following rubric can be used to assess students during each part of the activity. The term “expectations” here refers to the content, process and attitudinal goals for this activity. Evidence for understanding may be in the form of oral as well as written communication, both with the teacher as well as observed communication with other students. Specifics are listed in the table below.

1= exceeds expectations 2= meets expectations consistently 3= meets expectations occasionally 4= not meeting expectations

Engage Explore Explain 1 Shows leadership in the

discussion and offers creative ideas reflecting a good understanding of the physics behind the catapult.

Completes work accurately while providing an explanation for what is observed. Works very well independently.

Provides an in-depth explanation of findings, making good use of vocabulary terms. Fills out worksheet clearly.

2 Participates in the

brainstorm and shows an understanding of the physics related to the catapult.

Completes work accurately and works productively.

Provides clear explanation of findings. Fills out worksheet clearly.

3 Contributes to the

brainstorm, but shows little understanding of catapult physics.

Works independently, but makes some mistakes with the procedure.

Provides a limited explanation of findings. Fills out some of the worksheet.

4 Does not participate in

brainstorm. Shows no understanding of catapult physics.

Has trouble staying on task. Does little to complete the procedure.

Is not clear in explanation of findings. Does not fill out worksheet.

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Extension Activities:

• Have the students graph their data they collected.

• Challenge questions are listed on the following three pages.

Catapult (CT1/CT2) Science Challenge

The science challenge questions are designed to relate science content to the FSEA projects. Some of the questions relate specifically to the project. Others, though related, may go well beyond the project. Questions may vary in complexity, but teachers and mentors are encouraged to introduce these concepts to students. The intent is to provide discussion material at the completion of the hands-on project. It is suggested that questions be handed out at the first session and then discussed by the students and facilitators at the final session. It would also be a good idea to give the students the questions with the answers after the discussion.

1. Name the various forms of energy involved in the catapult.

Answer: You need to give the catapult energy. This energy comes from you, in the form of kinetic energy, when you push down on the catapult. The catapult then stores this energy in the rubber band or bending wood. When the catapult is released, the potential energy is transferred to the marshmallow, which moves through the air (kinetic energy). Air molecules bump into the moving marshmallow and slow it down. This energy is converted into heat and sound energy. When the marshmallow hits the ground, the energy is transferred to the ground in the form motion, heat, and sound. It is not a lot of energy, so the amount of motion, heat, and sound is small.

2. Draw a diagram of the marshmallow after it is launched in the air,

showing with arrows the forces that are pushing or pulling on it. What eventually happens to the marshmallow? Why?

Push from Catapult Air Resistance

Air Pressure

Weight (Gravity)

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The marshmallow will eventually fall to the ground as it loses energy and the air resistance and weight become greater.

3. What class of lever was your catapult? Support your answer by

drawing and explaining where the fulcrum, load, and effort were.

Answer: It is a class 2 lever. This is because the fulcrum is in the front, the load in the middle, and the effort at the back.

Effort

Load

Fulcrum

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Supplemental Information:

Competition Target: Diameter of the target tubes is as follows: You can determine the distances for each event You can also award the team that can shoot the farthest distance

Scoring

Event 1 Event 2 Event 3 Inner 3 6 9 Middle 2 4 6 Outer 1 2 3

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Scoring Sheet

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