# Energy Transfer: Engineering Catapults

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## Objective

The student will be able to describe and model situations in which different amounts of potential energy are stored in a system and support the claim that when the kinetic energy of an object changes, that energy has been transferred to or from the objects in the system.

#### Big Idea

Students use their understanding of kinetic and potential energy to design catapults using easily accessible materials that launch marshmallows!

## Introduction and Connection to the NGSS and Common Core

This is a two to three day lesson in which students explore potential and kinetic energy transfer as they use the engineering design process to build catapults that launch marshmallows for distance and accuracy.

This lesson is geared to address the following NGSS and Common Core Standards:

MS-PS3-2  Develop a model to describe that when the arrangement of objects interacting at a distance changes, different amounts of potential energy are stored in the system.

MS-PS3-5  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-ETS1-1  Define the criteria and constraints of a design problem with sufficient precision to ensure a successful solution, taking into account relevant scientific principles and potential impacts on people and the natural environment that may limit possible solutions.

MS-ETS1-2. Evaluate competing design solutions using a systematic process to determine how well they meet the criteria and constraints of the problem.

MS-ETS1-3. Analyze data from tests to determine similarities and differences among several design solutions to identify the best characteristics of each that can be combined into a new solution to better meet the criteria for success.

MS-ETS1-4. Develop a model to generate data for iterative testing and modification of a proposed object, tool, or process

CCSS.ELA-LITERACY.RST.6-8.1  Cite specific textual evidence to support analysis of science and technical texts.

CCSS.ELA-LITERACY.WHST.6-8.1.B  Support claim(s) with logical reasoning and relevant, accurate data and evidence that demonstrate an understanding of the topic or text, using credible sources.

Science and Engineering Practices:

As students go through the engineering design process, they create catapults that can shoot  marshmallows.  In doing this, they apply scientific principles to design, construct and test a tool or system (SP6).  In addition, in the warm up, students construct graphical displays of data to create linear relationships (SP4).  Moreover, as students write an explanation of their findings after completing this activity, students construct written arguments supported by data and scientific reasoning (SP7).

Crosscutting Concepts:

Designing catapults also can provide students with practice in Cross Cutting Concepts of “Systems and Models” as well as “Energy and Matter”.  Students use the catapults as a model that can show the input and output of energy and track how energy flows within the system (CCC Systems and Models).  As they notice the relationship between potential and kinetic energy, students notice that energy may take different forms and that the transfer of energy can be tracked as energy flows (CCC Energy and Matter).

## Warm Up Day 1: Constructing Graphs From Data Formative Assessment

10 minutes

To begin, students complete a formative assessment asking them to create a graph from a set of data.  The data included in this formative assessment is referring to a lab the students completed in the Rubber Band Cannon Lab. While it would be nice if students had completed this lab, it is not essential in order for students to create the graph.  So, you can still use this even if your students have not completed the actual Rubber Band Cannon Lab.

Notice that the student included a title that includes the variables, have labels with units on the x and y axis, have a key, and have placed the independent variable on the x axis and the dependent variable on the y axis.

## Warm Up Day 2: Sound Like a Scientist Sorting Student Work

10 minutes

Cut each of the student samples in this document into slips of paper.  Make enough copies for each pair of students to have a set.  Ask students to sort the slips in order of "Sounds Like a 7th Grader" to "Sounds Like a Scientist".  Once the students have sorted the slips, ask them to discuss their reasoning for their choices.

Rotate around the room and interact with students about their choices.  Students at the middle school level are very task driven; they will try to simply sort the stack without discussing their reasoning. And, this discussion is the key to the success of this activity.

Once students have ordered the student samples, have groups share for the class the reasons for their decisions.

The key is that students begin to develop an understanding of the importance of a formal tone in scientific writing.  Students recognize that when writing in a formal tone they should use strong nouns and verbs (using science vocabulary, writing in the third person rather than using words like it, them, they, I, we, etc.).

**The document included here has many examples of student samples that can be sorted.  You can use these extra examples on various days.  I typically do 1 or 2 sorting examples in a lesson.  The repetition of the activity allows the students to gain confidence in their reasoning.

Below are some of the examples of what students may specifically say about each response.

Samples A:

#1a:  A student dropped a scoop of sugar into a beaker of water.  This is how they described what they saw.

The molecules dissolved in the water.

Students say that this "sounds more like a scientist" than the other response because it uses scientific words like 'molecules' and 'dissolved'.

#2a:  A student dropped a scoop of sugar into a beaker of water.  This is how they described what they saw.

They spread out into the hot water.

Students say that this "sounds more like a 7th grader" because of the vagueness of the words 'they' and 'spread out'.

Samples B:

#2b:  Lab Question:  What is the relationship between the temperature of the solvent and the rate of dissolving of a solid?  Why is this?

It goes faster because they move around faster and bump into each other more.

Students say that this "sounds more like a 7th grader" because of the vagueness of the words 'It' 'goes faster', and 'they'.

#1b:  Lab Question:  What is the relationship between the temperature of the solvent and the rate of dissolving of a solid?  Why is this?

At a higher temperature, the rate of dissolving increasing because the molecules are moving around faster and bumping into each other more.

Students say that this "sounds more like a scientist" than the other response because it uses scientific words like 'rate of dissolving', 'higher temperature', and 'molecules'.  Some strong writers may recognize that the student uses a transition at the beginning of the sentence.

Samples C:

#1c:  A student placed sugar in hot water and cold water and measured how long it took for the sugar to dissolve.  Lab Question:  What is the relationship between the temperature of the solvent and the rate of dissolving of a solid?

Yes, because the molecules move faster.

Students say that this "sounds more like a 7th grader" because the student does not write a full thought and does not actually answer the question.  At this point, I discuss with the students the effectiveness of repeating part of the question (I call it RPQ) to help in making sure their answers serve the purpose of the question.

#2c:  A student placed sugar in hot water and cold water and measured how long it took for the sugar to dissolve.  Lab Question:  What is the relationship between the temperature of the solvent and the rate of dissolving of a solid?

As the temperature of the solvent increases, the rate of dissolving of a solid increases.

Students say that this "sounds more like a scientist" than the other response because uses strong science vocabulary and answers the question because it clearly states the relationship.

#3c:  A student placed sugar in hot water and cold water and measured how long it took for the sugar to dissolve.  Lab Question:  What is the relationship between the temperature of the solvent and the rate of dissolving of a solid?

The sugar went faster in the hot water.

Students say that this "sounds more like a 7th grader" because the student does not clearly answer the question, it merely states what occured in the lab.  It does not actually reference the relationship.  In addition, students note that stronger vocabulary could be used ("went faster").

Samples D:

#1d:  Lab Question:  What is the relationship between the temperature of the solvent and the rate of dissolving of a solid?

hotter = faster

Students say that this "sounds more like a 7th grader" because the student does not write a full sentence.  At this point, I discuss with the students the effectiveness of repeating part of the question (I call it RPQ) to help in making sure their answers serve the purpose of the question.

#2d:  Lab Question:  What is the relationship between the temperature of the solvent and the rate of dissolving of a solid?

The hotter the faster.

Students say that this "sounds more like a 7th grader" because the student does not write a full sentence.  At this point, I discuss with the students the effectiveness of repeating part of the question (I call it RPQ) to help in making sure their answers serve the purpose of the question.

#3d:  Lab Question:  What is the relationship between the temperature of the solvent and the rate of dissolving of a solid?

As the temperature of the solvent increases, the rate of dissolving of a solid increases.

Students say that this "sounds more like a scientist" than the other response because uses strong science vocabulary ('solvent', 'rate of dissolving') and answers the question because it clearly states the relationship.

Here is a notes sheet you could provide to the students about "Sounding Like a Scientist".  This notes sheet includes the skills/learning targets I have created, feel free to remove or change to meet your needs!

## Connecting to the Essential Question: What are you going to learn today?

5 minutes

Ask students, "What are you going to be learning today?".  Students should respond with the essential question, "How does energy transfer through various systems in the natural world?" (I keep this posted on the board.  Students also have it in their Unit Plan).

Explain that the students should specifically be connecting to Skills 2 and 5 listed in the Unit Plan:

2.  I can describe and model situations in which different amounts of potential energy are stored in a system.  (ex.  Elastic, gravitational, magnetic, chemical, etc.)

5.  I can support the claim that when the kinetic energy of an object changes, that energy has been transferred to or from the objects in the system (energy is conserved).

Ask the students to take some time to reread each skill.  In a previous lesson, students had self-assessed their level of mastery on a scale of 1 to 4 (4 being mastery).  As students have been through a couple of lessons dealing with these skills, ask them to re-assess themselves and change the number if they feel their level of mastery has increased.

Then, ask the students to make as many connections during the lab to the following ideas/concepts:

1.  How the potential energy stored in objects can change based on their position or arrangement

2.  Energy transferring from one object to another object

3.  How the amount of potential energy in a system affects the amount of kinetic energy that the system can have

Remind them if at any point during the lab they connect to any of these ideas, they should share that connection with you or a fellow student!

## Mini Lesson: Constraints and Choosing a Design Based on Criteria

15 minutes

Let the students know that over the next days they will be designing catapults that can launch marshmallows the longest distance possible and can hit a target for accuracy as well.

Say something like, “When engineers begin a design project, they must consider the constraints.  Constraints are rules or guidelines that must be followed.  You see, engineers don’t always get to just build their best idea.  There are many factors that can limit the possible solutions.  For example, the client might ask an engineer to build something in a certain amount of time, with specific materials, and with a certain amount of money.  In addition, engineers are always considering the safety and environmental effects of their designs.  Keeping these constraints in mind when designing will help guide your design decisions.”

Explain the constraints of this design challenge.

1.  Materials:

• One Cardboard Shoe Box (or cardboard)
• Rubber bands (up to 4)
• Popsicle Sticks (up to 4)
• One 12 inch piece of Masking Tape
• One Plastic Spoon
• Ruler
• Scissors
• 2 Marshmallows

2.  Materials can be cut (other than marshmallows).

3.  All materials do not have to be utilized.

4.  When launching, one hand may be holding the box steady and one hand (not two) can be touching the spoon.  The emphasis here is that you may not have two hands on the spoon at the time of launch. (This is important.  Without this constraint, students could simply hold up the spoon, pull it back and launch it without having to consider a design.)

5.  Students will have 60 minutes to build and test before official launches.

Say, “When engineers design and work in a team, they strategically choose the design they build first.  They don't just build the first idea that comes in their head.  They base their decisions on criteria identified by the team as being important for success.   In this particular challenge, there are three main criteria that I have found to be important for student success.  One is the amount of potential energy your design is able to store in the system.  Remember the amount of energy stored in the system will affect how much kinetic energy your system can generate.  The second is stability.  It the marshmallow is not stable at launch and the materials "wobble", energy is lost and the marshmallow does not travel as you will want it to.  The third is the practicality of the design.  You must consider if your design can actually be completed within the time constraint with the materials provided.  Some students sketch designs that are great ideas, but are so complicated that they are difficult to execute effectively.

Have students look at their Catapult Design Matrix.

Say, “Each row represents a student in your group’s design idea.  The columns represent the criteria I mentioned are the most important to consider.  Each member of the group will then describe their design to the group and explain why they think that it will work.  Then, each member of the group will rank the design on a scale of 1 – 4 (4 being the best) for each design principle.  Add each column up and place the total in the last column.  After each member’s design has been ranked, choose the design (based on data) that will be the first prototype you build!  Now, if Student A’s design has the highest total, but Student B’s design had one criteria or concept that was better than Student A’s, by all means, add it!”

Provide students with time to sketch their own design idea prior to meeting with their group.  If you have them sketch after meeting with their group, students ideas will be influenced by others.  I find it best to have them sketch before any interaction with group members so that every students initial instincts can be displayed.

Once students are done sketching, have them get in groups of 2 – 4 and complete the design matrix.  Following the completion of the design matrix, students should show you their matrix and the sketch of the prototype they will be building.  Only at that point do I allow students to get their materials.

## Engineering Design Challenge: Catapults

80 minutes

As students begin designing, make sure the target is visible and you have a "launch pad" setup for practice.  It is vital to the design process that the students can launch and make alterations to their designs based on results, in order to create an optimum design.  Emphasize this part of the process to the students as well.

Students launch their catapults from on top of a table.  I hang the target (it looks like a bulls eye) on the wall in the hallway and have the “Distance Launch Pad” set up near the “Target Practice” but launching in the opposite direction.  The “Target Practice” table is about 15 feet from the target on the wall.

After designing and altering designs, students should let you know when they are ready for their “official launches”.  Official Launches consist of the following:

1. Three attempts to meet/pass the “target distance”.
2. Three attempts to hit the bulls eye on the target.

A couple of teacher tips:

1.  Marshmallows work better when they are hard and dried out!  On Day 1 (or the day before), open the bag of marshmallows and let them sit overnight.
2. You will need a place to launch a distance.  I launch in the hallway, the classroom just isn’t enough space.
3. On the distance measurement, make a decision about whether you are going to measure where the marshmallow lands or where it stops after rolling.  I always go with where it stops after rolling, but you can make your own call!
4. You should create your own “target distance” after watching students launch their designs.  I find that 25 feet is appropriate, but you should move the line accordingly to fit what you feel is a proficient distance amongst the groups in your class.
5. While I am only assessing to see if they make the distance or hit the bulls eye, students love to compete!  Often the groups whose marshmallows travel the farthest want to measure their exact distances to compare to other groups.  And, those groups that have very accurate catapults want to add up the total points accumulated when launching towards the bulls eye target.
6. If you plan on doing this design challenge each year, ask for shoe boxes from your students at the start of the school year.  Even if you aren't going to do the challenge until March, asking for shoe boxes from families in the beginning of the year is helpful because that is a time many students get new shoes!

Example Target Practice:

Example Distance Launches:

Notice that this is the same design as the Target Launch in the video above.  Although this design was very effective for target practice, its distance was not effective.  Students would need to make alterations in their designs in order to meet both criteria.

In this design, the students broke the spoon to make more of a slingshot as opposed to a trebuchet.  Students designs will vary greatly!  This student's design is very effective; although one thing to notice is one factor students will end up having to adjust as they test is the angle at which the marshmallows are launched.  In this case, the marshmallow hits the ceiling.

## Engineering Design Challenge: Constructing Explanations Student Work

30 minutes

Student Design Matrix:

Students in this group each shared their design ideas and ranked each other on their designs based on criteria.  In this case, Paige's design resulted in the highest ranking.  It is important to note that while this group did build Paige's design, they also incorporated some of Fred's "Ease of Construction" ideas to help allow the group to execute Paige's design within the time constraint.

Student ABCDE Paragraph:

One important thing to notice is that the student writes in third person and maintains a formal tone.  She avoids using words like "he, she, we, I, it, etc.".  After completing the Day 2 Warm Up on "Sounding Like a Scientist", this is an important aspect to provide students feedback on so that the students begin to apply the ideas presented in this warm up.  In the following video, I talk about some of the important things to look for in the student's scientific writing for this ABCDE paragraph.

Catapult Connections Page 1:

For this page, students are asked to apply what they know about this design challenge to a student that is going to use this challenge for a different purpose.  This document along with the following page are an opportunity for students to review variables and how they relate to charts and graphs.  Students identify the independent and dependent variables.  In addition, they calculate gravitational potential energy.  Students are provided with calculators, formulas, and all relevant information to do this.  This is not indicating students should memorize how to calculate GPE.  It is merely an opportunity for students to use relevant data for scientific calculations.

Catapult Connections Page 2:

Questions 1, 2, and 3:  In previous lessons, students have learned about the relationship between graphs and variables.  The first three questions ask the students to recognize that the independent variable is located on the x axis while the dependent variable is included on the y axis.  In addition, it is important to note that when the student defines independent variable in the second question, they do not say, "It is the variable that changes."  This is the common response middle school students give when describing the independent variable.  However, in an experiment, the dependent variable changes as well.  Thus, explaining the independent variable in this manner will end up causing misconceptions later.  The student in this document explains the independent variable by asking the questions, "Everything was kept the same in every trial except...".  This indicates that the student has an understanding that the independent variable is the variable that is manipulated and that all other variables are held constant by the scientist.  The student then indicates in the third question that the dependent variable is the variable that is measured in the results of the experiment.

Questions 4:  The fourth question asks the students to identify other factors that impact the gravitational potential energy stored in a system.  The experiment described in this document was referring to the height of the launch.  Thus, when recognizing that gravitational potential energy was calculated by multiplying mass times height times gravitational acceleration on Page 1 of this document, the student answers that the amount of mass and amount of gravity could be variables used to test gravitational potential energy.

Question 5:  The student here indicates that the greatest potential energy was located at the top of the projectiles height and that the projectile had a high kinetic energy at the second it was launched.  In addition, the student shows that as the projectile went up, its GPE was increasing while its kinetic energy was decreasing and vice versa on its downward path.  This question really goes to the heart of the idea that students are tracking the flow of energy through a system as it transfers from one type of energy to another.

## Closure: Connecting Catapults to Kinetic and Potential Energy

5 minutes

At the beginning of the lesson, the students were asked to connect to the following ideas:

1.  How the potential energy stored in objects can change based on their position or arrangement.

2.  Energy transferring from one object to another object.

3.  How the amount of potential energy in a system affects the amount of kinetic energy that the system can have.

Have students turn to a partner and share a point in the lab that they connected to each of the above concepts.