Type of Resource | Class activity
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Topic | Other |
Taxa | Vertebrate
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Organizational Level | Organismal
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Estimated time to do activity | 5 minutes |
Background required/level | Any |
Role of activity in your course | I bring it in when I talk about the properties of materials--it brings home the relevance of Young's modulus, strain energy storage, and resilience. I return to it later, when talking about maximum output of humans, in particular the power and force we can get from our muscles. |
What students might learn from this course or activity | Concepts: distinguishing among at least three properties of materials, the practical implications of the limitations of humans as engines, the use of biomechanically-based calculations to make assertions about the history of technology. |
Special tools, equipment or software needed | No special material is needed, but (assuming one has access to a saber saw and electric drill at least) one should anticipate spending $10 or $20 on wood, rope, screws, etc. Allow, say, half a day for building and testing. |
Safety precautions, possible permissions necessary | None. |
Miscellaneous advice - pitfalls to avoid | Some adjusting may be needed to ensure that the projectile goes through the hole in the front frame. Don't try shooting water balloons until that aspect of performance is reliable.
I think the thing could be built with machine screws and wingnuts in a form that collapses for travel--one mainly needs to make the front frame removable. With negligible use of metal, it should not bother airline inspections especially. |
Frequently asked questions by students | They ask about scaling the thing up; I suggest a Google search of "ballista" and "ballistae," with, of course, the usual skepticism about the trust one puts in unvetted sources. |
Evaluation | Not specifically. It does, at the least, enliven a lecture, either for class or as a visitor elsewhere. |
Description | A simple, tabletop model of this bit of ancient artillery illustrates the way collagen can provide elastic energy storage--as it does in running. It also raises biomechanical questions that students can address with appropriate calculations--the weight of tendon needed for a specified shot, the frequency with which two artillerymen could shoot projectiles, and the dimensions of the capstan-turning rig they must have used. |
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