Next, I instruct groups to take their two A, two B and two C cups inside a large metal bin. Students also grab a brick and a watering can. Have each team carefully turn over one of their A cups and place it in the metal bin.
Next, I direct students to slowly pull the cups off, leaving the damp sand. Then one student from each group will pour water on his/her building using the watering can. Students record what they observed. Did their buildings remain standing? What does the water from the watering can represent? (Answer: Rain or erosion.)
Next, each group sets up their second A building in the metal bin in the same way they did with the first one. This time they try and set the brick on top of the building. Ask the students what they observed and record in their science notebooks. Is the building able to hold up the brick? What do they think the brick represents? (Answer: The brick represents the weight of people, furniture and other objects [loads] that the structure must hold up.
Next, students get one of their B buildings and place it on the ground. They tear away the cup from the sand, water and glue mixture very carefully. Then one student from each group pours water on their B building using the watering can. Again, students record what they observed. Did the building remain standing? Did it hold up better or worse than the A buildings? Why did this building do better? (Answer: The glue helped hold the sand together.)
Each group sets up their second B building in the metal bin in the same way they did with the first one. Have them try and set the brick on top of the building. Students record what they observed. Does the building hold up the brick?
Next, for buildings that are still standing, have groups hold their bricks 6 inches above their buildings. On the count of 3, students drop a brick on each building. Students then describe their observations in their science notebooks. Students repeat the above procedures for each C building.
Listen in as these students talks about what happened to their bricks when water was poured on.
To end the lesson, I lead a discussion about how well the C buildings did compared to the A and the B buildings.
I ask students to think about the situation if they had to live in a sand house: would they want live in a house like building A, B or C? Engineers also often must consider materials cost and other factors when building a house. Which of these buildings is the most expensive to build?
I discuss with students how engineers must constantly weigh the pros and cons of a particular design to come up with the best design. For example, we could build buildings out of titanium since it is incredibly strong; however, we do not actually build them out of titanium since it is so expensive and buildings do not need to be that strong in order for us to safely live in them.