Building Lab: Balconies and Awnings

Have your students ever thought about what makes balconies and awnings stable and safe structures? 

Vocabulary

Cantilever A projecting structure supported at only one end, such as a shelf bracket or diving board.

Activities

Place a heavy book in a bag with straps. Have students first place the bag straps over their arms near the shoulder, and then over the tips of their fingers. Is it equally easy to support the weight in both places? 

They should see that it is much easier to support the bag close to the shoulder, near the fixed base of the cantilever, then at the unsupported fingertip end. A cantilever, such as in balconies and awnings, can support more weight closer to its fixed end.

Have various household materials available and have your students build a business front with a balcony or an awning and make sure that they use something to serve as the cantilever.

Building Lab: Tunnels

Building Lab: Tunnels

One challenge of tunnel engineering is to be precise to ensure that teams building from each end of the tunnel come together in the middle. These activity shows students the importance of communicating precisely, and then an activity on measuring accurately.

The Peanut-Butter Sandwich Activity

Their first challenge is to give the instructions for a simple task, such as making a peanut-butter sandwich. Have one person, such as the teacher, stand in front of the class with the materials to make a peanut-butter sandwich. Have your students, one at a time, give instructions on how to make the sandwich, but make sure you follow their instructions exactly. For example, if they say, "Put the peanut-butter on the bread," then you take the jar of peanut butter and place it on the loaf of bread. Though this hilarious activity, your students will get better at giving precise instructions.

The Building Activity

Break your students into pairs and give each pair an identical set of a dozen or so blocks of different shapes and colors. Have the pair sit back to back and have one in each pair build something with the blocks.

Once the first student has built something, he next has to describe to his partner how to make the identical project without either partner seeing what the other is doing. Once they are done, they can look at the projects and compare them and, if they are not identical, identify where the communication broke down and what they could do in the future to prevent this error. Have them switch roles and do it again.

The Measurement Activity

For this next activity, you will need two plain white paper plates for each student. Students again pair up and sit back to back. Each student marks a circle of the size of his choice (under 3 inches) on their first paper plate at any place he wishes. Give them some time afterwards to consider how to accurately explain how to describe where his circle, or the entrance to the tunnel is, so that he can be able to help his partner make an identical sized circle in the identical place on his second paper plate. Provide rulers and have them make measurements so that they can effectively give accurate descriptions to their partners.

Once they are finished with their preparations, have the students give their partners descriptions and measurements and have the partners make as accurately as they can an identical circle on their second (blank) paper plates. Are the circles identical and in an identical place? Have them switch roles and do the activity again.

If your students are having a difficult time, suggest to them that they make some way of dividing the paper plates (such as dividing the paper plates with straight lines to make 8 identical sections and shade one of the sections in so that they each have a starting point) so that they have the ability to give more descriptions. Do their tunnel circles meet up?

Building Lab, Part 8: Dams and Water Pressure

Water pressure increases with the depth of the water. In deep water, there is more water "piled up," which causes the pressure to be greater at the bottom than at the surface. A dam's design must enable it to withstand greater pressure at the bottom than at the top. As a result, many dams are built in a triangular shape. The wide bottom withstands the great load of the water deep below the surface, while the top of the dam can be built thinner so as not to use unnecessary costly materials.

For greater details on this demonstration, see School for Champions

Demonstration

Poke three holes in the side of a milk carton and cover them with a single strip of tape. Fill the carton with water. Hold the carton with one hand and quickly pull off the tape. The water will stream out of each hole with different force. Explain that water behind a dam is a live load pressing on the dam. The greater the amount of water built up, the greater the pressure–so the water coming from the bottom hole has more force than the water from the top hole.

Brainstorm

Water discharging from the bottom of a dam has great force. Have your students brainstorm ways in which to release the pressure and have them illustrate their ideas. They may suggest using multiple spouts, a triangular spout to release the water, or using a "diffuser", which is a structure that is used to break the stream of water, sometimes as simple as just a mass of large boulders.

Build a Dam
You are part of a team of engineers given the challenge of building a system to dam up 5 liters of water in a classroom trough. You'll have lots of materials to use such as cardboard, pvc pipes, tape, foil, plastic wrap, cups, straws, paper clips, wooden dowels, cotton balls, plastic sheets, clothes pins, wire, string, screen, fabric, springs, other readily available materials. You have a base of gravel at the bottom of the trough which simulated the rocky or sandy bottom of a river bed. You'll need to not only stop the water, but develop a system so that you can release a little at a time in a controlled way. You'll need to stop the water, let a little come through, and stop it again. Plan and build a dam model, using the instructions found at Try Engineering. 

Building Lab, Part 7:Towers

Many forces are at work on towers. Gravity and the dead load of the tower push down, the ground pushes back up, and small air movements push from the side. A foundation distributes the load into the surrounding ground material and can help balance the sideways wind force. The size of the foundation depends on the strength of the supporting ground. A foundation placed in rock can be smaller than a foundation placed in sand or mud.

Challenge your students this week to build the tallest tower they can. You can use any materials you like, such as blown up balloons, uncooked spaghetti or newspapers and tape.  Remind students to think all the ways they can alter the materials they are working with. Encourage them to think about shapes and stability. Reinforce that this is not a competition between groups, but rather a chance to learn from others' discoveries so that looking at what other groups are doing is good. Remind them that they may use the tape to stiffen the materials such as paper, particularly at the base, or to hold stable shapes such as triangles or columns together.  

As groups finish and measure their towers, everyone should be encouraged take a group tour of the results, thinking about the creations in terms of what forces are affecting these towers. The dead load of the tower are pushing down, the surface is pushing back up, and small air movements are adding forces from the side. What different solutions did groups come up with to counteract these forces? What is similar about the taller structures? Encourage students to point out creative uses of shapes, fastening techniques, wide bases, and other solutions to balancing and stiffening their towers.

Building Lab, Part VI: Geodesic Domes:Triangles, Toothpick Structures and Dowel Designs

Have kids form domes by bending a few sheets of newspaper into a bowl shape. They will quickly note that the domes cannot support much of a live load. 

Which shape is more stable, a triangle or a square?

What shapes do you think would make the domes that are the most sturdy and support the most load? Guide your students into discovering that triangles are the most stable shape by building them. Help them to understand that this is so because compression acting at one joint is balanced by tension along the opposite side.

Making Structures out of Toothpicks and Gumdrops.

Have your students begin building a bridge (without trusses) by constructed a rectangular box of toothpicks and gumdrops. Test the bridge's stability by pressing down on it and wiggling it, Is it stable?

If not, challenge them to add more materials to strengthen the box with trusses. A truss is a rigid frame composed of short, straight pieces joined to form a series of triangles or other stable shapes. They can add cross-pieces and triangular braces.  Next, have your students extended their trusses to see how wide a gap they could make that still could be stable. 

Finally, have your students build miniature geodesic domes using the gumdrops and toothpicks. 

After the lesson, I let them go whichever way they wanted to with the materials and they had a wonderful time being creative and their structures just kept on growing!

What's the strongest dome you can build out of newspaper?

The Power of Buttresses

A dome is a curved roof enclosing a circular space. It is a three-dimensional arch. How can  you strengthen a dome?

Have five students stand in a circle around a ball, placing their fingertips on t he ball and lifting it towards the center of the circle, sliding back their feet. Reach into the center and push down gently on the ball. Ask your students where the dome could use more support. They may come up with the idea themselves, but if they don't, have a student sit at the feet of each student in the dome, around the outside edge, forming a buttress. As in an arch, the buttresses exert an inward force on the sides of the dome that balances the outward force created by the load pressing down on the top of the arch.) 

Making a Paper Geodesic Dome

A geodesic dome is a dome formed by joining triangles together. You can build a giant geodesic dome out of newspaper. First, gather some friends or family members to help you.

What You Will Need

• many newspapers

• masking tape

• measuring tape

Have your students predict how many magazines you think your newspaper dome will be able to support.

A dome must support its own dead load as well as the live load of wind, rain, snow, or ice. The geodesic dome's strength is due to the fact that triangles, as we have seen, are very stable shapes. The geodesic dome's design distributes loads over all of the different triangles within its design.

The task of this week was to build a structure that would stand out of newspaper and tape only. The dowels are just made from newspapers rolled up and taped together.

How strong is your dome? Did the results surprise you? Why or why not? What was the hardest part about creating the dome?

How could you make your dome stronger without interrupting the space underneath it? Make a prediction and test it. 

Building Lab, Part V: Cables and Suspension Bridges

When thinking about building, your student might not think too much about the role of cables, however they are vital to a suspension bridge. A suspension bridge's cables and towers transmit the dead load of the bridge deck and the live load of traffic to the massive anchor blocks at each end of the bridge. The tension in the cables leading up from the bridge deck is balanced by the tension in the cables leading to the anchor blocks, as well as the compression in the towers. The anchor blocks must be massive enough to resist the tension in the cables caused by the weight of the bridge deck. 

Cable Demonstration

In order to demonstrate how cables can work to use the mechanical advantage that pulleys provide, you need some rope, a smooth stick like a broom handle or walking stick and some students.

Tie one end of a rope on a smooth stick like a broom handle or walking stick. Next, loop it around another stick and have the person holding the first stick to hold onto the remaining rope. It will look like this picture. 

Now, stand about three feet apart. You will need to let out some rope.

Once it is set up, have both people pull back on each broom, and you use the end of the rope to try to pull them together. It is hard to pull them together.

But, if you loop the rope first around the stick twice, it is so much easier to pull the two together this time.

Even your youngest student can pull heavier students or family members together.

source
Chesapeake Bay Bridge

Discuss how this design can also work with cables and bridges, converting the pulling-down force into a force that pulls up on the weight. 

Now that we have already looked at beam bridges, we want to look at suspension bridges and the differences between the two.

Students should find that adding the cables to their straw bridge and anchoring the cables on both sides significantly increases the load that the bridge can support. 

Make a model of a beam bridge by taping two straws together at one end.  At the other end, tape the straws together with a small piece of straw as a spacer, making a tall triangle out of straws. 
Make two sets of these, These are the two towers of the bridge. Tape these to chairs and then place another straw on top of the spacers to form a beam bridge. 
Next make a load tester by hanging a cup from the beam, and then take begin putting coins in the cup. It should hold a fair amount (about 15 coins) before the beam bends, dropping its load.

Next make a suspension bridge to compare how much it can hold. Tie the center of a length of thread around the middle of a new straw and place the straw between the towers. Pass each end of the thread or "cable" over a tower and down the other side. Pull the cable tight and anchor it on the table. The cup of the suspension bridge should hold many more coins (our held over 25 coins) and the bridge should be able to hold even more weight once the cup is filled. The difference in the ability of the bridges to hold weight and the importance of cables in larger bridges (with much heavier loads) should be easy for your students to see.

Building Lab, part 3: Columns and Arches

What role does the column take in architecture and building? Columns are often used to hold up heavy loads such as the roofs of buildings, which pushes on the column, putting it in compression. Therefore, a good column, then has to be very strong in compression.

Can a toilet paper tube then support your weight? 

Tell your students that you are going to have them place an empty dishpan, tray, or box lid on the floor, and then they are to stand an empty toilet-paper tube (the column) on one end in the pan. While holding on to the back of the chair with both hands, they will gradually press straight down on the top of the column with one foot. Have them predict whether a toilet-paper tube can withstand the compression caused by their weight. Have them explain the reason for their prediction.

Note: If your students are very young (and light) they may be able to stand on the toilet paper tube without collapsing it. This is because the tube is round and is able to distribute the compression all around evenly. If this happens to you, have an older, heavier student test it, and then you, the teacher could also test it. 

Once you do have a collapsed tube, have your students observe it to see where it failed. Have your students now brainstorm ways in which they could make the column stronger, using only tape and sand? Repeat standing on the column, using the second toilet-paper tube and your new design.

How did the strength of the two columns compare? Have your students think about why the results of the two were different. Next, tape the ends of the tube and fill it with sand. The tube now can distribute the compression of the weight outward from each sand grain and can now hold the weight, not only of your heaviest student but of an adult as well without collapsing. Wonder how much weight it would hold before it collapsed?

What can this experiment tell us about the best building materials?

For Older Students

Use the tubes to discuss circumference, diameter, and area of circles. Ask students to predict which can support a greater weight: a single column with a circumference of 24 cm or three columns with circumferences of 8 cm each? Have them test their predictions. Students will probably find that the answer depends on how they arrange the columns. Three smaller columns arranged a small distance apart in a triangular shape may support more weight than a single large central column.

Arches

An arch is a curved structure that converts the downward compression force of its own weight, and of any weight pressing down on top of it, into a force along its curve. This results in an outward and downward force along the sides and base of the arch. 

A buttress is a side support that counteracts an outward pushing force, the way bookends keep books on a shelf from sliding sideways. Buttresses are often used to support the sides of arches and tall cathedral walls, where they counteract the outward thrust.
Have two students form an arch by placing their palms together and leaning toward each other, sliding their feet as far back as they can. Caution them not to lose their balance. Ask the students where they feel a push or a pull. Next have a third student gently pull down on the top of the arch to test its strength. They should find it not too difficult to break the arch.
Now guide them to the idea of adding buttresses by asking additional students to reinforce the legs and feet of the arch-makers. Ask the how stable their legs feel now. They should see a large difference in their ability to resist the pull at the top of the arch now.

Building Lab, Part I: Compression, Tension and Torsion in Building Materials

In order for students to understand how to choose the best building materials for the project they choose to build, students must understand how physical science comes into play. Forces act on building materials in many ways, and to help students learn about this, they can perform hands-on tests on basic building materials that can be found around the house, and then apply what they have learned to analyzing actual building structures. But first they must first learn some vocabulary words.

Compression (Squeezing)

Compression is a force that squeezes a material together, which tends to make the material become shorter. The lower columns of a skyscraper, for example, are compressed by the heavy weight above them.

Tension (Stretching)

Tension is a force that stretches a material apart which tends to make the material become longer. For example, the cables in a suspension bridge have the weight of the roadway and all the cars traveling on it pulling on them, creating tension on the cables.

Bending

When a straight material becomes curved, one side squeezes together and the other side stretches apart. This action is called bending. The top side of the metal bar is pulled apart in tension, and the bottom side is squeezed together in compression. This combination of opposite forces produces an action called bending.

Shear (Sliding)

Shear is a force that causes parts of a material to slide past one another in opposite directions. For example, during an earthquake, parts of a roadway can shear or slide in opposite directions.

Torsion (Twisting)

Torsion is an action that twists a material. For example, a bridge can twist violently in strong winds and collapse. The twisting force is called torsion. 

Builders Need to Know Their Materials

Different materials have varying abilities to withstand compression, tension, and torsion. Students can get a chance to test materials around the house to learn about these terms and about the building materials. Send your students on a scavenger hunt to find building materials such as yarn, popsicle sticks, pipe cleaners, clay, sponges, erasers, rubber bands, paper-towel tubes, pencils, cardboard, aluminum foil, drinking straws, tiles, or cloth.

Testing the Materials

Students can perform three tests on the materials gathered to determine the tension, compression and torsion abilities of each of the samples. 

Tension: To test the material in tension, pull on it or tug it from both ends.

Compression: To test the material in compression, push it together from both ends.

Torsion: To test the material in torsion, twist the two ends in different directions.

Demonstrate how to test the materials by choosing one and tug, push and twist on the sample to test tension, compression and torsion. For example, using a rope to demonstrate the tests, have two kids tug on the ends of a rope (tension), then push the ends together (compression), and finally twist the ends of the rope (torsion). They should find that the rope is strong in tension but weak in compression and torsion.

Now have each student pick a few items from what they have gathered and predict which ones will be strongest in tension, which in compression and which in torsion.

Now, have them test the materials by performing the same tests which you had demonstrated on them. Students will have to help each other in pairs to accomplish this. Then they should record their findings, ranking the materials from 1-4 (1 Very weak! It crumples or breaks with hardly any force. 2 Only fair—it can't withstand much force. 3 Pretty good—it takes a lot of force to break it. 4 Super strong! We can't break it.) They should find that the materials that are strongest in tension:  are the string, yarn, pipe cleaner, popsicle stick, ceramic tile, cardboard, drinking straw, cloth, rubber band (strong but very flexible), rubber eraser, paper-towel tubes and the pencil. The materials that are strongest in compression are the popsicle stick, clay (limited), ceramic tile, rubber eraser, paper-towel tubes (limited) and the pencil. The materials that are strongest in torsion are the ceramic tile, rubber eraser (limited), paper-towel tubes and the pencil.

Discussion

Which materials were strongest in resisting each type of force? Did any of these results surprise you? Why or why not? 

Which materials were strongest across all three tests? How would you describe those materials?

Discuss how some materials are flexible under a type of stress–they change shape as opposed to breaking outright. When might flexibility be desirable? When is stiffness required? (Parts of structures such as the cables of suspension bridges that are built to withstand shaking caused by wind gusts often have some "give." Other parts of structures, such as floor beams that support great weights, need to be rigid.)