Exploratorium Field Trip Pathways

Teacher Version

Strength and Stability

The following California State Science Standards are relevant to this Pathway:

Grade Topic Subsection
3 Investigation and Experimentation 5.d
4 Investigation and Experimentation 6.d, f
5 Investigation and Experimentation 6.b, h
6 Investigation and Experimentation 7.a

California State Standards

What makes a structure stand up? Why doesn't it fall down? What makes one structure stronger or flimsier than another one? What about the structure of our bodies? How come WE don't just fall down every time we try to walk? This Pathway looks at some of the ways in which some objects stay put, or stay in one piece!

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Catenary Arch
  1. Does the completed arch seem strong or stable to you?
    The completed arch does NOT seem very strong or stable, but there is a hidden strength in it. If a string was carefully laid over the top of the arch, the arch will withstand a surprisingly strong, gentle pull on the string ends.

  2. What happens when you don’t put the blocks in numerical order?
    When the blocks are not in order, they do not form the arch shape. (Each block has a slightly different angle cut on the top and bottom so the higher blocks tilt in more.)

  3. Instead of an arch, try building a tower. Draw what it looks like.
    Drawings may vary. Here are two possible results.

Beam Bridges

  1. Which beam supports your weight better?
    The beam with the longer edge vertical, not horizontal.

  2. Pick up both beams and switch their places so the beam that was lying flat is now on its side. Which beam supports your weight better now?
    Again, the beam with the longer edge vertical, not horizontal. (The way the beam is placed makes the difference, not the beam itself.)

  3. How are the two beams different?
    One is thinner and taller; one is wider and shorter.

  4. Draw what happens when someone stands in the middle of a beam.
  5. Draw what happens when someone stands near the end of a beam.


Take It from the Top
  1. Can you get the entire block to stick out beyond the length of the bottom block? Draw it.

Balance the Stick

Notice that you can slide the weight up and down.

When is the stick easier to balance—with the weight high or the weight low?
Though you might think it's easier to balance with the weight lower, it's actually easier with the weight higher. This is because the weight is further from the pivot point, and so it falls more slowly. This quality of "angular momentum" is similar to why a figure skater slows down as he/she extends his/her body outward from the axis of their spin.


Center of Gravity
  1. Do your hands move smoothly together, or with stops and starts?
    Stops and starts. This is because the weight over each hand is constantly changing as both move toward the center. More weight (mass X gravity) on one side means more friction needs to be overcome, and so the stop. When there is more weight on the other side, it starts again.

  2. When your hands come together, are you balancing the stick?

  3. What do you think makes one hand stop while the other keeps moving?
    Friction causes one hand to stop moving. The force of friction increases as the weight of an object increases, so when you feel one side of the stick get heavier, the increased friction stops the movement of that hand.

  4. Try it with two people (using one hand each). What happens?
    Should still work.