Physics Week Two

In our second week of co-op physics, we got an introduction to structural engineering.  Working in groups, we first constructed four different geometric shapes from straws and pipe cleaners - a cube, a rectangular pyramid, a triangular prism, and a triangular pyramid. 

(Apparently, it is a universal tendency to wear these things as hats)

Then we measured the dimensions and calculated the respective volumes and efficiency.  This challenged some math skills as well, mine included!  Our very simplified version of comparing efficiency was to find out which figure had the highest volume using the smallest amount of "building material."  (Spoiler alert:  the cube was most efficient.) 

But which shape is strongest?  If we'd had access to a small spring scale and hanging weights, we could have tested this ourselves.  Instead, we used logic and experience to discuss it, and came to the conclusion that the triangular shapes are stronger than the cube shapes.  This is because triangles can redistribute stress and load.  Load on one angle can be shared with the other two angles.  Rectangular shapes can be reinforced and made more rigid by adding diagonals.  This redistributes load to not only the other angles of that triangle shape, but to any adjacent triangles as well.

How does this apply to building structures, like bridges or buildings?  Rectangular shapes provide the most volume, and generally the most usable space, so to give rectangular buildings and structures more strength and stability, diagonal rods, cables, or braces are added to the framework to form those triangles.  Bridges are built with diagonal trusses to add strength and stability.





We briefly discussed how domes and arches provide lots of space and structural stability because of the even distribution of stress and load, and were used extensively by the ancient Romans in their largest building projects - aqueducts and stadia.  However, there's an important limit to these shapes - they needed equally large supporting walls.  The geodesic dome is a combination of the dome shape and triangle shapes in an extremely durable and efficient structure.  Well-known examples of geodesic domes include many large sports venues, and of course the iconic Spaceship Earth at Disney's EPCOT.

   

Then we talked a little bit more about load and how structural engineers need to consider the load path from the top of a building down to the foundation.  Each level must support the downward force from all the levels above it.  A foundation transfers the load of a structure into the ground, therefore the taller the structure, the more the load that is being driven downwards.  This is also important for buildings to withstand the dynamic loads of earthquakes or hurricanes. 

For the remainder of the class time, we challenged the students to put this knowledge to work by either playing Jenga or trying to construct the tallest building or longest bridge using the straws and pipe cleaners.

The ideas for the straw and pipe cleaner structures and their comparisons came from the Teachers Guide Straw Structures from Pitsco Education.

I also found lots of helpful information at one of my favorite websites - How Stuff Works.

This is the second post in a series.  I shared the lesson from Week One here.

Do you have fun ideas for learning about physics? Please share them in the comments section.

 Don't miss a coffee break! Subscribe to Homeschool Coffee Break by Email! 

 ©2006-2015 Homeschool Coffee Break. All rights reserved. All text, photographs, artwork, and other content may not be reproduced or transmitted in any form without the written consent of the author.http://kympossibleblog.blogspot.com/