Summary As an introduction to the concepts of tension and compression, participants use their bodies to act out building shapes and understand the forces of push and pull. Next, they observe the forces of compression by manipulating gelatin blocks. Finally, they look at photographs of buildings in their neighborhood and identify the forces of push and pull at play. Learning Goals for Everyone Cognitive Goals Define a force as a push or a pull. Describe tension and compression using the terms push and pull. Identify forces of push and pull at play in neighborhood buildings. Identify tension and compression in a structure. Affective Goals Demonstrate engagement by asking questions, responding to questions, and looking alert. Behavioral Goals Use their bodies to act out building shapes and the forces of push and pull. Manipulate gelatin blocks to demonstrate and observe compression. Document session experiences and thoughts by adding to their sketchbooks. Learning Goals for Caregivers Tension and compression are important structural words. All structures whether a tent or a skyscraper, a dome or bridge exist at all times in either tension or compression. A balance (or equilibrium) of opposing forces is what makes a building stand up. Unbalanced forces signify instability and can lead to a building s collapse. Cognitive Goals 35 Minutes Affective Goals Behavioral Goals Practice serving as a coach and scaffolding children s learning. Books (any size, shape, or weight), for use in the compression demonstration Cameras Gelatin activity materials (see sidebar on page 2 for recipe) Large rubber ball (no smaller than a basketball or kickball) Pencils and other drawing materials Photos (found online) illustrating tension and compression Examples: steel cables of an elevator (tension) pedestal of the Statue of Liberty (compression) suspension bridge cables (tension) bridge towers (compression) stones of an arch bridge (compression) the dome of the U. S. Capitol (tension and compression) Sketchbooks Styrofoam (one piece of foam for each family) The Built Environment and All Content 2009 Chicago Children s Museum 1
Gelatin Shape Recipe Materials 4 packets of clear unflavored gelatin (such as Knox) 1 pinch sugar 1-1/4 cup boiling water Plastic ice cube trays and/or cookie sheets Directions Mix all dry ingredients together. Boil water. Add boiling water to dry ingredients and stir slowly for three minutes. DO NOT MAKE BUBBLES. Pour mixture into ice cube trays and cookie sheets. When filling ice cube trays, fill each cube to the same level but don t let tops run together. HINT: It may be easier to pour mixture if you first put it into a measuring cup with a spout. Get rid of any bubbles that may have formed, by poking with a utensil. CAUTION: Tray with mixture is hot. Handle with potholder. Put tray in refrigerator, NOT FREEZER, and wait one hour until fully set. To remove cubes, use finger or butter knife to release. Bricks will be sturdy, so pry away. See diagram below for suggested cutouts of cookie sheets. HINT: Wash tray and cookie sheets before reusing for second batch. Note: This activity was adapted from Steven Caney s Ultimate Building Book by Steven Caney (October 2006, Running Press Kids). Arch Column Compress Dome Gravity Horizontal Load Structure Tension Vertical Space Requirements: One room with some open space for participants to move around during the session Staff Requirements: 1-2 facilitators Prior to the Session: Prepare photographs of buildings in the neighborhood. Prepare the pans of gelatin and cut different sizes and shapes for participants. Prepare photos that illustrate the concepts noted in the Materials list. Introduction: Materials: N/A A curved structure that serves as a support (show shape by drawing on board) A supporting pillar, consisting of a base, shaft, and capital To press together or force into smaller space; condense; compact A hemispherical roof or ceiling (show shape by drawing on board) The force that pulls things toward the earth Parallel to the horizon Something that is supported by a structure Something that is constructed A stretching force that pulls on a material Perpendicular to the horizon 5 Minutes If your group completed Session 1: Orientation, review the highlights. Remind participants that they will be working together to learn about the built environment and will use their sketchbooks to reflect on their own learning. Introduce today s lesson about push and pull (compression and tension). If you were here last time, you might remember that we talked about ways that parents could coach their children, what we wanted to learn about buildings, and how we could use our sketchbooks to record what we re thinking and doing. Last week, we tried to guess how buildings stand upright. Today, we re going to look at two different forces that act on buildings. These forces are push and pull. Take the comparison between the invisible structure of buildings and the human skeleton a step further by having participants stand up and think about what is going on beneath their skin that allows them to stand. Possible Cut-Outs for Gelatin The Built Environment and All Content 2009 Chicago Children s Museum 2
Activity: 25 Minutes Materials: Rubber band, foam, rope, books, rubber ball, photographs, gelatin activity materials Introduce the terms tension and compression or pull and push. Give parent-child pairs rubber bands and a piece of foam to follow along with the demonstration. Invite children and parents to practice using their bodies to understand how it feels to be a building that is in push or pull. Have individuals place a few thick books on their heads to feel compression. Tension: Take a thin rubber band and pull it with your hands. What is happening to the rubber band? You are putting the rubber band in tension and the band becomes longer. Whenever a part of a structure becomes longer, it is in tension. Compression: Now take a piece of foam and push on it. What is happening to the foam? The foam becomes shorter in the direction in which you push. Whenever a part of a structure becomes shorter, it is in compression. The amount of lengthening and shortening in a structure is usually so small that is it is impossible to see it with your eye. But engineers and architects still need to make sure that these two things are balanced. Stand back-to-back with your partner. Gently lean or push on your partner. Think about how you feel. Face your partner and hold hands. Gently pull back. Think about how you feel. Are you balancing each other? What happens if one of you pushes or pulls too much? How do you think a building feels if something pushes or pulls on it? Let s be columns. Take a book and rest it on your head. Think about how your head feels with the book on it. How do you think it would feel if you put three books on your head? In order to be age-appropriate for children ages 5-8, use the words pull and push rather than tension and compression. Help kids make a personal connection to buildings by telling them that today they will have a chance to act like buildings and imagine how a building would feel if it were alive. Highlight the pressure, stretching, and bending that the participants feel. Discuss how these are the same forces that architects take into consideration in their work. Compare what they are feeling to a column. If they don t know what a column is, explain it and show a photograph. The Built Environment and All Content 2009 Chicago Children s Museum 3
Hold up a picture of an arch. Have two people lean against each other s hands. Test how far apart the partners can stand before the arch begins to collapse. Let s make arches. Face your partner again and press your hands against your partner s hands. Take a small step backward. Keep taking small steps backward until you can t press your hands with your partner s anymore. What shape are you in? Are you pushing or pulling? Compare this to an arch, which uses compression to balance its own weight and the weight piled on top of it. Show a picture of the St. Louis Arch (search online for a good image). Ask individuals to report where in their body they feel the most pressure. Give each pair a rope. Have groups create suspension bridges by having two people act as piers holding a rope as the bridge. Show a picture of a dome (or point to one in the environment). Take out the rubber ball. Ask the group to create a dome by having two people make an arch, leaning their hands against a large rubber ball. Keep adding pairs of individuals until there is no room. Then take the ball away and ask the group to report what happens. Now, let s make a bridge. Some bridges are made by having strong vertical pieces (indicate the piers in the photograph) that are connected by the other parts of the bridge. You are going to be the vertical pieces. That means you are standing up tall. The rope is what is going to connect you. Take turns standing closer to your partner and then farther away. How does your rope change as you and your partner move? What does this tell us about making a bridge? A bridge needs to have the right balance of tension and compression push and pull or else it will not be stable. Now let s all work together to make a dome. Has anyone ever seen a dome? (Participants create the dome.) Why did we all fall? Everybody fell down when I took the ball away because we were all pushing on the ball together and all our pushes were keeping it in place. Use the picture of the suspension bridge to illustrate this concept. Identify that the piers are being compressed, while the rope is under tension. Ask if there is more tension when the piers stand closer together or farther apart. Show participants the photograph of a dome. A dome works by using a combination of tension and compression. The Built Environment and All Content 2009 Chicago Children s Museum 4
Child explains how his building is experiencing compression. Introduce the next activity, the goal of which is to enable participants to observe compression by manipulating gelatin blocks. Let s take a closer look at tension and compression. I m going to give each group a tray of gelatin blocks and a book. Use the shapes to build a structure. Do you see the force of compression? Where? How does this compare to the force of push you felt when you were acting like buildings a few minutes ago? Note: Build with the gelatin blocks in the same way you would any toy building block system. The blocks formed from the ice cube trays can be stacked to create columns. The flat pieces can be used to form roofs and floors. See the sidebar on page 2 for the gelatin shape recipe. Friends collaborate on a tricky structure. Point out the books that the groups have as part of their materials. All building materials are subject to compression (and tension), even if we can t see the forces in action. It s happening and it impacts all materials. Some forces that cause compression include the loads of other building materials on top, the force of gravity, live people walking around, furniture, the roof, etc. Facilitator demonstrates compression using weight. Take a book and press on a gelatin block. What happens? Can you see the force of compression? (Point out that the block flattens and spreads out, due to the pressure upon it.) How do you think this compares to the force of push in real buildings in the neighborhood? The Built Environment and All Content 2009 Chicago Children s Museum 5
Facilitator and child consider how to put gelatin pieces together. Friends problem solve together. Invite the group to come back together. Ask participants to look at photographs of famous buildings that exemplify tension or compression. (Refer to the photos in the Materials list and print images of the structures from the Internet.) Ask the group to identify the forces of push and pull in the buildings. Let s look at these pictures. Let s see where we can find examples of tension and compression. Hints to identifying tension and compression in your photos: The point at which a roof connects to a wall is an example of compression (the roof is pushing down on the wall). The point at which a traffic light connects to the wires running over a street is an example of tension (the wire is being pulled by the traffic light). The floor of a building is an example of both tension AND compression. The load (e.g., people, furniture, other objects on the floor) pushes against it, while the walls pull it. Think about the examples that the participants have engaged in during the lesson and tie these into the observations of the photographs. For instance, if you are showing a building with columns, refer to the activity where participants were putting books on their heads to feel the tension of a column. Closure: 5 Minutes Materials: Sketchbooks, pencils and/or other drawing materials A finished gelatin building shows tension and compression. Ask participants to spend two minutes adding a page to their sketchbooks. Ask participants to focus on one thing that made them smile or laugh, one thing that surprised them, or one thing they question. They can add to their sketchbooks in the form of writing or a drawing. Now we are going to think about all we have done today. You acted out the forces of push and pull by pretending to be different structures. Then, we observed the force of push by playing with gelatin blocks. Did anything surprise you? What do you have questions about? Did anything make you laugh? (Pause here to share.) Encourage caregivers to serve as coaches and scribes as children complete their pages. Be sure to collect the sketchbooks before participants leave for the day. We re going to use our sketchbooks to write and draw about what you did and thought while you were working together. Caregivers: You can help by asking questions and being the scribe. Work together to figure out what you want to draw and write. The Built Environment and All Content 2009 Chicago Children s Museum 6
Distribute and describe the homework assignment. Today s homework lets you continue thinking about pulls and pushes, or tension and compression, that are all around us. Take a close look around your home. Tension and compression, or pulls and pushes, are everywhere! Be a tension and compression detective. Look at three different objects in your home: a table, a chair, and a bed. Imagine what it would feel like to be each of these things. What would it feel like to be a bed and have people jump on top of you? Encourage participants to do the activity, but remind them that it is optional. For the After-School or Classroom Teacher In the Introduction, ask students to share the homework they completed and their thoughts about the process of completing it. Encourage different students to take turns being partners as they practice being a building. The Closure section offers a good opportunity to have students Think, Pair, Share: Think about what they want to record in the sketchbook; Pair with a friend to talk about the idea; and Share it with the class. As an alternative to the suggested assignment, homework could be to reenact some of the session activities at home with a family member and then write about that experience. Acknowledgments The Built Environment was made possible thanks to a grant from the National Science Foundation. The Built Environment and All Content 2009 Chicago Children s Museum 7