If you drizzle salt into a pile on top of a triangular base, the pile will develop ridge lines. What's the geometry of those ridges? In this article, Willowcreek Middle School (Lehi, UT) teacher Troy Jones explores the geometric concepts within physical salt piles using triangles, quadrilaterals, and circles in several configurations.

This page features an article (PDF format), PowerPoint presentation, Geometer's Sketchpad file, and textbook reference for a classroom exploration of these concepts.

Troy developed these materials as part of the Park City Mathematics Institute, or PCMI. This year's institute is currently under way. See more projects, papers, and activities from PCMI here:

http://mathforum.org/pcmi/hstp/projects.html

Topics covered include:

Algebra

Functions
Logarithms
Polynomials
Quadratic theory
Recurrence relations

Calculus

Differentiation
Integration

Geometry

The circle
The straight line
Vectors

Trigonometry

Compound and multiple angles
Radians and Equations
Wave function

http://www.CTKMathGamesForKids.com/

This site presents a collection of Java-based interactive games and puzzles with mathematical contents and a few practice exercises disguised as games.

Alexander Bogomolny, the site's author, writes, "There are a few games whose purpose is to allow for a relaxation period before or after taking up the mathematical challenges. One does have to relax from time to time."