Slopes and Angles
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Slopes and Angles
Materials:
Sand
Gravel
Dirty clay
Cup
Amazing fact: If you slowly pour a cup of sand on one point ten different times, the resulting piles will always have the same shape.
Why is this? It has to do with the fact that every material has a specific "angle of repose." Engineers define this as the limiting steepness beyond which particles will slip downhill. In other words, a pile of sand cannot get any steeper than a certain angle, no matter how carefully you pour it. The angle is steeper for larger and irregular or wet particles. So gravel has a steeper angle of repose than sand, and sand has a steeper angle of repose than dry clay (which has finer particles). See for yourself with gravel, sand, and dirt in your garden or at the beach. Now then, what's your angle?
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| Mary White |
