Playground Design Teacher Guide

Unit

Playground Design

Subject

Engineering

Grade Level

ES 3-4

Activity Name(s)

Building a Bungee Jump

Building a Zip Line

Being Prepared

Both activities can be done individually, though at this age, working with a partner or small group will be more beneficial in nurturing collaboration, communication, and cooperation. Additionally, having a team to share ideas and jobs (such as holding sensors, releasing eggs, clicking the start and stop buttons on the graphs) makes things run more smoothly during the activities. At the 3rd and 4th grade level, it would be helpful to guide the groups in assigning team jobs so that everyone has ownership and responsibility in the activity, and so that the guidelines and expectations for behavior, respect, and participation are made clear for everyone in the group.

Before either activity, be sure to pre-teach the students about the sensors, proper use and care of them, and how to read the measurements and graphs produced. If the measurements and data are too confusing, then the activity will be overwhelming and somewhat meaningless to them. (And will require too much on-the-spot teaching during the activity from the teacher, which will not allow the students to be directing the discovery and investigation.)

Some students may be allergic to eggs! Plastic eggs filled with clay can be used as a substitution in both activities!

Materials Needed

• force sensor for Bungee Jump activity (Could be done with one, but two is better)
• motion sensor for Zip Line activity (One should be sufficient)
• sensor interface
• hard boiled eggs (2 per student group) or use plastic holiday eggs
• materials for building egg "harnesses" -- cardboard, egg carton, tissue paper, soda bottles cut in half, etc.
• markers 
• form or paper cups
• plastic baggies
• safety scissors
• thin elastic rubber bands
• index cards
• string
• fishing line or mono-filament wire
• paper clip, pulley, or wheel with groove cut in it (one per student group)
• meter stick

Getting Started

Prior to the bungee activity, the teacher may want to attach a force sensor to a meter stick to show students how they should do this properly (as an example). Better yet, since these sensors are delicate and expensive, the teacher might want to attach the sensors to the meter sticks for the students already in order to avoid them not being properly secured, since the sensors will then be dangled upside-down and have heavy eggs dropped from them. A poorly attached sensor might come off the meter stick and fall to the ground.

The first part of the zip line activity goes through the steps of setting up the motion sensor so that the egg is "big" enough for the sensor to see. If students have never used a motion sensor before, these numerous steps might be confusing. The teacher might want to go through this portion of the activity as a whole class, or perhaps go through this part of the activity as a "preview" the day before. The direction and pictures are very clear, but when students are excited to get started with an activity or experiment, they might accidentally "zip" through this part of the set up, which will cause greater confusion and unreadable results and graphs later.

Make sure to closely monitor students during the use of both sensors. They are delicate and expensive! The measurements and graphs can be confusing to students, and this is the most important part of the activity, so it is vital that they find it meaningful. Point out the patterns, the peaks, the inclines, and other trends.

What Students Need to Know:

Students need an operational definition of "force". At this age, students commonly believe that "force" is a property of an object. By now, they should understand that pushes or pulls can change the motion of an object. But they may not understand speeding up or slowing down happens because a force is exerted on an object. To keep it simple, you can avoid the word "acceleration" by defining force in this way:  A force is a push or pull upon an object that causes a change in motion of the object. In these two activities, students will explore systems where multiple forces are acting on an object (gravity, friction, tension, spring force). By 5th grade, you can introduce the idea that some forces cancel each other out, so there is zero net force on the object. This concept is probably too sophisticated for students in Grades 3-4, however. 

Suggested Timeline

Bungee

You should allow two hours for the activity itself, with additional time for any pre-teaching of necessary science concepts or sensor usage.

Zip Line

You should allow two hours for the activity itself, with additional time for any pre-teaching of necessary science concepts or sensor usage/set-up.

Additional time to allow for student problem solving and collaboration, and time for them to redesign, rebuild, and reflect on their results.

Thinking about the Discovery Questions

This unit is motivated by the discovery questions:

• Sometimes playground equipment and the features that make things safe to use are not fun, but why is it important to make things safe?
• What makes an object move along a zip line?

These two lessons address the concepts of momentum, gravity, friction/resistance, force/motion (push/pull as a force), inertia of objects in relation to their mass.

With regards to teaching this unit teachers may think they need to give all directions and not let kids work it out (such as telling them how tight to make their zip line, how steady to hold the sensor, to be sure one fixed point of the zip is higher than the other, etc.). It is important that students are allowed to work out design problems with the teacher asking directed questions that may help the student focus on the design process and the concepts involved.

Misconceptions

Misconceptions about force and motion center around some critical understandings. Students at this grade level tend to think of force as a property of an object (i.e., "An object has force). It helps if they have a simple operational definition of "force", such as "A force is a push or pull on an object that causes a change in the motion of the object." In addition, research shows that students often hold the erroneous belief that a force acts only in the direction of motion. This activity provides an ideal opportunity to talk about opposing forces acting on the dropped egg and on the zip line rider. Students may confuse inertia with speed. They may think a school bus has less inertia because it is harder to move, but more mass actually means more inertia. At the same time they may believe that heavy things will be slow and light things will be fast. A misconception related to friction relates to the importance of friction in everyday activities. Students commonly believe that objects resist acceleration from their state of rest because of friction -- that is, they confound inertia with friction. Friction is a force --  without it we couldn't change direction or stop. Last, kids may believe that designing playground toys and equipment is nothing but fun & games. While playground designers DO have fun, they also pay close attention to safety. If someone makes the choice to jump off a swing-set and gets hurt, that is using the equipment inappropriately. However, if the swing-set was built poorly it could break or tangle someone in it. If a child who is properly using the equipment gets hurt, the designer is responsible for that injury. Play equipment such as a bungee jump/harness system allows a person to experience a thrill of leaping much higher or falling longer distances than would otherwise be possible using the elastic bungee cord to stretch and pull the rider safely along their thrilling ride. If that equipment were to fail, a very serious injury could result.

Learning Objectives

NGSS

• Performance Expectations
  • 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.
  • 3-PS2-2. Make observations and/or measurements of an object's motion to provide evidence that that a pattern can be used to predict future motion.
  • 3-5-ETS1-1. Define a simple design problem reflecting a need or a want that includes specified criteria for success and constraints on materials, time, or cost.
  • 3-5-ETS1-2. Generate and compare multiple possible solutions to a problem based on how well each is likely to meet the criteria and constraints of the problem.
  • 3-5-ETS1-3. Plan and carry out fair tests in which variables are controlled and failure points are considered to identify aspects of a model or prototype that can be improved.
• Disciplinary Core Ideas
  • ES-PS2: Motion and Stability: Forces and Interactions
    • PS2.A: Forces and Mation
      • Each force acts on one particular object and has both strength and a direction. An object at rest typically has multiple forces acting on it, but they add to give zero net force on the object. Forces that do not sum to zero can cause changes in the object’s speed or direction of motion. (Boundary: Qualitative and conceptual, but not quantitative addition of forces are used at this level.) (3-PS2-1)
      • The patterns of an object’s motion in various situations can be observed and measured; when that past motion exhibits a regular pattern, future motion can be predicted from it. (Boundary: Technical terms, such as magnitude, velocity, momentum, and vector quantity, are not introduced at this level, but the concept that some quantities need both size and direction to be described is developed.) (3-PS2-2)
    • PS2.B: Types of Interactions
      • Objects in contact exert forces on each other. (3-PS2-1)
  • ES-ETS1: Engineering Design
    • Defining and Delimiting an Engineering Problem
      • Possible solutions to a problem are limited by available materials and resources (constraints). The success of a designed solution is determined by considering the desired features of a solution (criteria). Different proposals for solutions can be compared on the basis of how well each one meets the specified criteria for success or how well each takes the constraints into account. (3-5-ETS1-1) (secondary to 4-PS3-4)
    • Developing Possible Solutions
      • Research on a problem should be carried out before beginning to design a solution. Testing a solution involves investigating how well it performs under a range of likely conditions. (3-5-ETS1-2)
      • At whatever stage, communicating with peers about proposed solutions is an important part of the design process, and shared ideas can lead to improved designs. (3-5-ETS1-2)
      • Tests are often designed to identify failure points or difficulties, which suggest the elements of the design that need to be improved. (3-5-ETS1-3)
    • Optimizing the Design Solution
      • Different solutions need to be tested in order to determine which of them best solves the problem, given the criteria and the constraints. (3-5-ETS1-3) (secondary to 4- PS4-3)
• Practices
  • Asking questions and defining problems
    • Define a design problem that can be solved through the development of an object, tool, process or system and includes multiple criteria and constraints, including scientific knowledge that may limit possible solutions.
  • Planning and carrying out investigations
    • Plan an investigation individually and collaboratively, and in the design: identify independent and dependent variables and controls, what tools are needed to do the gathering, how measurements will be recorded, and how many data are needed to support a claim.
    • Collect data to produce data to serve as the basis for evidence to answer scientific questions or test design solutions under a range of conditions.
  • Constructing explanations and designing solutions
    • Undertake a design project, engaging in the design cycle, to construct and/or implement a solution that meets specific design criteria and constraints.
    • Optimize performance of a design by prioritizing criteria, making tradeoffs, testing, revising, and re- testing.
• Crosscutting Concepts
  • Patterns
    • Students recognize that macroscopic patterns are related to the nature of microscopic and atomic-level structure. They identify patterns in rates of change and other numerical relationships that provide information about natural and human designed systems. They use patterns to identify cause and effect relationships, and use graphs and charts to identify patterns in data.
  • Cause and effect
    • Students classify relationships as causal or correlational, and recognize that correlation does not necessarily imply causation. They use cause and effect relationships to predict phenomena in natural or designed systems. They also understand that phenomena may have more than one cause, and some cause and effect relationships in systems can only be described using probability.

NSES

• NSES Science as Inquiry – Abilities necessary to scientific inquiry
  • Employ tools to gather data and extend the senses to measure weight and force.
• NSES Physical Science – Position and motion of objects
  • An object's motion can be described by tracing and measuring its position over time.
  • The position and motion of objects can be changed by pushing or pulling. The size of the change is related to the strength of the push or pull.
  • The position of an object can be described by locating it relative to another object or the background.

Discussion: Setting the Stage

• Have you ever been on a zip line? What did it look like?

  Answers will vary, observant students might say it had a dip at the bottom, was not incredibly taught, used a pulley, harnesses.

• What helped you move down the zip line?

  Answers may include gravity, wheels in the zip line, or running and jumping into/onto it. Astute students may notice that they could "zip" faster if the line was greased or friction reduced somehow. 

• How do you stop at the end of a zip line?

  Answers may include a guide, a platform to land on, a bumper of some kind, or the ground.

• Have you ever been on a boardwalk/carnival/state fair bungee jump ride? What did it look like?

  Descriptions may include a giant rubber bands, a trampoline, or a harness.

• Did it look like fun, or did it look scary? (If students have never seen a bungee jump, you may want to find an appropriate video clip of someone bungee jumping to share with them, so they have a common point of reference.)

  Responses will vary.

• What safety precautions are in place to keep a bungee jumper safe?

  Answers may include a guide or instructor, harness, perhaps a student will mention that the cords will be monitored for any fraying or wear, or helmets.

• What other rides or playground equipment needs to be build with safety measures or precautions in mind? Ask for specific examples.

  Answers will vary.

Discussion: Formative Questions

Bungee Jump

• Is your bungee short enough that the egg/harness will not hit the floor?

  You may need to hold the force sensor/meter stick from a higher starting point.

• Are you using the same height as a starting point for your repeated trials?

  Use a second meter stick to be sure, or be sure to release level with the meter stick that the sensor is attached to. Avoid accidentally having the meter stick and sensor bounce off the chair backs during the bungee jump! You may want to secure the ends of the meter stick to the chair backs, or have team members hold the meter stick on the chair backs.

• Are you dropping the egg, as in simply releasing it from your fingers, or are you giving it an added push?

  You only want to drop it each trial in order to test for the results of this bungee jump! Teachers: An interesting extension activity could be done by moving the meter stick to a higher starting point, then asking students to gently give the egg harness a downward push. They can compare the results to their data from the egg drop without an initial push. This can be a springboard to a great discussion about applied force.

Zip Line

• How can I keep the motion sensor steady and make sure it can "see" the egg on the zip line?

  Attach the sensor to one of the fixed points; add something such as an index card to the egg/harness to make it a larger target for the sensor to see.

• How will I protect my egg from breaking on the zip line and in the bungee jump?

  Build a strong, protective harness from the materials available. Students may want to consider that in a real world ride, people will not spend 20 minutes getting in and out of the harness.

• How tight does my zip line need to be?

  If it is too loose, the ride will be more of a free fall, but if it is too tight, the "rider" will crash in to the end point with too much force. A slightly loose dip at the end is best.

• How should I space my two fixed points on my zip line?

  See the question/answer above, and space according to the amount of fish wire available.

• How will I attach my zip line harness to the rubber bands/paperclip that will run on the fish wire zip line?

  Securely, but without increasing the friction between the paperclip and the fish wire zip line.

• How will I tell if the zip line is exerting a push and pull on my egg by viewing the motion sensor graph?

  The graph will not be a straight steady declining line, but rather a declining wave, almost a downhill pulsing wave, and the egg somewhat bounces down the zip line (due not only to friction between the paperclip and the fish wire, but also in part to a probable push by the student when releasing the egg at the top of the zip line).

Discussion: Wrapping Up

• How did the force change as the egg bounced on the bungee cord?

  Students should see larger and then increasingly smaller and smaller spikes on the graph, until it levels out.

• Look for the highest spike during the bungee drop, this is the greatest force exerted on the egg. When did this occur? Why did the force decrease after this spike?

  The biggest spike/greatest force was the first drop. This was due to gravity. The elasticity of the bungee (rubber bands) absorbed some of the inertia after each bounce, giving the egg less force each time, until eventually it stopped bouncing all together. Until students got the zip line arranged correctly (how tight, how much higher to have the start from the finish, where to place and hold the sensor, how to affix the egg/harness for a smooth zip that the sensor could easily "see"), the graph was likely difficult to read with accurate results. Engineering activities with children require allowing them to go through a trial and error process of working things out for themselves so that they can see what works and what doesn't work. It is a very important part of the process! Let them work together, discuss with their team, collaborate, and reflect. Avoid letting them look on at another group that may have figured out a working method, or they will miss out on the opportunity to creatively think of a solution themselves!

• Was your graph a perfectly straight downhill line, or did it have "bumps and waves" in it? What would explain either result?

  A straight line means the egg zipped smoothly with little friction, a bumpy or wavy graph means the egg bounced due to friction or getting hitched and caught up on the zip (this might also be due in part to being slightly pushed upon release at the top of the zip line).

Additional Background

Friction is a force that acts on objects, slows down motion, and causes inefficiency. The zip line the students created, in order to operate smoothly, would need to overcome most of its friction. Force is a push or a pull, and many forces are acting on you all of the time. Usually you don't even realize that the force of gravity is acting on you, but it is, all of the time. If you are falling, it's pretty obvious that something is pulling you down but even if you are standing on the floor, perfectly still, the force of gravity is still pulling you down. And the really hard thing to understand is, if you are standing perfectly still on the floor, the floor is pushing up on you just as hard as gravity is pulling you down! Gravity is always pulling a load (such as the the egg) toward the center of the Earth. Each successive bounce of the rubber band bungee will have less height because the rubber band's elasticity is absorbing some of the egg's inertia and force.

Content Support for Teachers:  

For a refresher on forces, try The Physics Classroom free interactive online tutorials. This link takes you to "The Meaning of Force", a good overview of forces acting at a distance (such as gravity) and contact forces (such as friction, tension, spring force, and applied force.)  www.physicsclassroom.com/class/newtlaws/Lesson-2/Types-of-Forces

Analysis

Zip Line

1. Is there a push and pull on the egg to make it move?

   Yes, the force of gravity. Teachers: As the rider continues down the zip line, a combination of resistive forces act to slow the rider down. The most significant of these resistive forces is friction. The rider also experiences air resistance. In addition, there is a tension force between the harness and the object that holds it to the line. 

2. In testing your zip line, were any of your eggs cracked or broken? Why?

   Answers will vary, breaks may be due to poorly built harnesses, improperly held ends of the zip line, a zip lime that was too steep or too taught causing it to move too fast at the final impact.

3. When your zip line worked the best, what did the position graph look like?

   Answers will very, but should include a description of the slope of the line, for example the graphed line was not steeply sloped and moved up and down just a little.

Bungee

1. Describe the pattern on the graph.

   The graph of the first bounce should show the greatest force, with each subsequent bounce measuring less and less force, until the the egg comes to a still position.

2. At what point in the ride does the egg feel the most force? A. When it reachers the lowest point of the first drop and is initially yanked back up in the opposite direction by the elasticity of the rubber band bungee to its highest rebound point. Q: In testing your egg bungee jump, were any of your eggs cracked or broken? Why?

   Answers will vary. Possible responses may include breaks do to poorly built harnesses, improper attachment of the harness to the bungee, a bungee that was too long causing it to hit the ground, or improper set up of the meter stick/chair/ sensor, causing the set up to jiggle or bounce during testing.

Further Investigation

Bungee

Students are going to need a safe way to build a bungee up to the ceiling. The teacher's assistance will definitely be needed. If the school has a stairwell that would work for this, that would be excellent. An engineering and problem solving opportunity arises in considering the length of the cord before and during the jump given the weight of the egg or eggs in the harness, the additional forces present with the higher drop, and any reinforcing needed to where the harness attaches to the bungee. Again, the teacher may want to ensure the sensor to properly used and protected, as dropped from this increased height will certainly damage or destroy it. Plastic eggs filled with clay may be preferable for this Further Investigation, unless numerous additional eggs are made available for trial and error purposes.

Zip Line

If numerous groups are working on the Further Investigation activity simultaneously, it may be appropriate to to coordinate their zip line courses so they do not intersect or tangle. If students have correctly figured out the correct "tightness" of a good zip line, and then have their longer zip lines use a similar dip at the end, then their eggs should not impact the end point with such great force as to crack or break the eggs (especially if their harnesses are still properly build!). It bears repeating, that if the teacher has opted to embrace the true engineering and design model, to involve student problem solving and collaboration, an an entire additional day to redesign, rebuild, and reflect is suggested.

A Further Investigation for these physical concepts, as well as the engineering concepts, covered in this unit could also extend to roller coasters. The teacher might want to consider using a simulation, such as the Energy Skate Park: http://phet.colorado.edu/en/contributions/view/3083