Online manipulatives suitable for K-12 students. Includes number & operations, algebra, geometry, measurement, and data analysis & probability. Site made available through Utah State University. A downloadable desktop version is also available.
"MathMovesU.com will supplement your classroom curriculum. It's designed to help middle school math students practice and improve their math skills. MMU combines stuff kids are into like music, sports & fashion with algebra, geometry, decimals, fractions & word problems."
One important quality of a skateboard is its flex, how far the deck will bend when weight is put on it, and how well it snaps back to its original shape.