Clay Beams and Columns

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If the more open-ended activity is done in a center as suggested above, it is best to have students write about their experience. Have them respond to some of the questions on the previous page.

For the demonstration part of this activity, ask your students what they observed when looking at the large and small clay beams. Which was stiffer? Which was stronger? Which bent over the fastest? Ask them why they think the clay beams behaved differently on the two scales.

Ask them how much more clay there is in the big beam (64 times as much). Ask them how much more the big beam weighs (64 times the weight). Ask them how much greater the area of the base (or cross-sectional area) is for the big beam (16 times the area). Ask them how much stronger the big beam is (16 times as strong). Then ask if this helps explain why things were different on the two scales.

The linear dimensions of the big clay beams are 4 times that of the small clay beams. They are 4 times as long, 4 times as wide, and 4 times as thick. This means that the volume of the big beam is 4 X 4 X 4 = 64 times the volume of the small beam. This means 64 times as much clay which is 64 times as heavy.

The area of the big beam is 4 X 4 = 16 times the area of the small beam. Since strength depends on the area of the cross-section of a beam or column, the big clay beam is 16 times as strong as the little clay beam. The increase of the volume (64 times) of the big clay beam over the little clay beam is 4 times as great as the increase of area (16 times). This means that the increase in weight of the big beam over the little beam is 4 times as great as the increase in strength. The big beam cannot easily support its own weight and collapses and bends much more than the small beam.

• When building clay trees and animals with large versus small clay trunks or legs, your students find a number of differences. Have them bring in pictures of actual large and small trees and animals to look for similar differences.