The Mighty, Mighty Triangle

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The SWBAT explore the idea that wide bases add stability to structures.

Big Idea

Structures need strength and stability. Wide bases, such as a triangle, add stability.

Teacher Notes

Activity Description

The children have learned some of the basics of building from studying the Watts Towers.  Now they are working to find out Simon Rodia's secret--that wide bases are very stable.   Working with a partner,  one person first puts their feet together and has their partner gently push on them.  Then they repeat with their legs apart.  Through this activity, they will find out that wide bases are more stable.  The concept will be further explained by looking at photos of objects and buildings with wide bases.  To wrap up, we will discuss the essential question for this unit.

NGSS/Common Core Connections

This lesson is a prerequisite lesson for tower building.  The children need some background knowledge as to what shapes make strong design components.  The NGSS standard connection is discovering the structure and function of designed objects are related the their function.




5 minutes

I try to incorporate what we have been learning to our lesson today.

We have been having so much fun learning about towers. Simon Rodia, the man who built the Watts Towers, did so without any formal training.  But he knew a secret of building…something that made his towers very strong.  He knew what shapes and forms to use to make his towers sturdy.  We are going to try to figure out this "secret.”

Anytime you mention the word "secret" to second graders, they are all in.  Everyone wants to know secrets.  Even the reluctant learners perk up to learn more.



30 minutes

I have the students work with the My Clock Buddies.  They need to decide where they would like to work and then go by their partner.  I have the pairs either choose the number one or two.  

Then I instruct student 1 to stand with his/her legs together.  I have partner 2 use three fingers to  gently push on their partner (see video clip--unstability).  The children quickly find out that it is very easy to make their partner lose his/her balance. Here is another video clip where the partners figure out that when pushed, you bend a little bit.  

Then I have that same person (partner 1) stand with his/her legs apart and the partner 2 gently pushes again only using three fingers. It is fun seeing the children's reactions to this little investigation (see she's not moving at all video clip).  In this video clip is that same partner group explaining what happened to them.

To make sure everyone understands the main concept, I have two children come up and demonstrate.  I love how this usually very shy girl gave a good explanation of our investigation in this video clip.  It is so wonderful to see what happens when science comes "alive" to the children.

Was it was harder to keep your balance with your legs apart or together?  

This girl gave a great summary of our findings.

We discuss their feeling and findings.  They are able to relate the idea that if the legs are apart, they were more stable.  



30 minutes

 Then to help explain the concept, we brainstorm as a class the things that have wide bases for stability.  They certainly came up with interesting things with wide bases from a bottle to tree trunks.  It is great to see how the demonstration has helped them to understand the concept.  

Here are some photos of items with wide bases that I use to further explain stability.

Traffic Cone photo

pyramid photo


A frame house



We take a look at each of these items and discuss. Then I show the children posters of famous towers (see resources--Famous Tower Posters).  I ask the following questions:

  • What do the towers have in common? (They are wider at the base and narrower at the top). 
  • What do they think makes them stable? (A wide base)
  • What do you notice about the shape of the base?  (Triangular or rectangular)
  • Are there any geometric shapes that are used often? (Triangles) 

What shape were you most like when your legs were spread apart?

They are already understanding that things with a wide base are more stable.  Now I want them to take it one step further and relate this to a triangular shape.   To further explain the ideas of the lesson, we visit a website called Building Big.  On the website is an activity that the children can do to find out how strong the triangle is.



10 minutes

To wrap-up today's lesson, we discuss and summarize what we have learned today.  I have the children first have a short discussion with their partner on what makes structures stable (discussing with partners video).  Then we reconvene and discuss the ideas further.  

Then I pull up the Essential Question on the Smartboard.  We discuss what makes structures strong and stable.  I want the children to add the idea to their learning that wide bases add stability to a structure.  From our discussion I can see that we are ready to move on to the next lesson, to further explore these concepts.