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I ♥ Parabola - Poster
PARABOLA Bridges are physical manifestations of a parabola. The height-versustime graph of falling objects at or near the center of the earth can be modeled by a parabola as well. It is usually the first nonlinear curve that students study in algebra. A parabola can be defined as the locus of points equidistant from a point (called the focus) and a line (called the directrix). The parabola with vertex at the origin and opening upward has the equation 4 py = x2, where p is a constant representing the distance from the focus to the vertex (or the vertex to the directrix).
I ♥ Truncated Icosahedrons - Poster
TRUNCATED ICOSAHEDRON An icosahedron is one of the five Platonic solids (tetrahedron, cube, octahedron, and dodecadhedron are the others). The 20 faces of the icosahedron are congruent equilateral triangles. If planes sliced the icosahedrons at the 1/3 point of each edge, each triangle would become a hexagon, and a pentagon would replace each vertex of the original icosahedron.
The soccer ball and the ball used in the Olympic sport of team handball is an example of a spherical rounded analog of a truncated icosahedron. The flexibility of the surface of these balls and the air pressure on their contents results in this familiar round shape.
I ♥ Fibonacci Numbers - Poster
FIBONACCI NUMBERS The Fibonacci sequence, 1, 1, 2, 3, 5, 8, 13, 21, 34, . . . , where the first two terms in the sequence are each 1 and every successive term is the sum of the two previous terms.
The ratio of successive terms approaches the golden ratio, ø = (1 + √5) / 2 ≈ 1.6803399. Fibonacci numbers occur often in nature, in particular in phyllotaxy, the study of leaf arrangement on a stem. The spirals on sunflower seed heads, on pineapples, and in pine cones are invariably Fibonacci numbers or multiples of Fibonacci numbers.
I ♥ Logarithmic Spirals - Poster
LOGARITHMIC SPIRAL The logarithmic spiral is a polar curve whose equation is given by r = a e , where bθ a and b are constants.
The nautilus shell is the best-known example of the logarithmic spiral found in nature, but flying animals will approach targets by using a logarithmic spiral pattern. Raptors will hawk prey, swifts will attack insects, and insects will approach a light source via a logarithmic spiral. Beaches can form in the shape of a logarithmic spiral, and the arms of tropical storms can also model this shape. The logarithmic spiral has close connections to the golden ratio.
I ♥ Rotational Symmetry - Poster
ROTATIONAL SYMMETRY Starfish, jellyfish, and buttercup flowers are among the natural organisms that demonstrate rotational symmetry. Objects that exhibit rotational symmetry can be rotated (less than 360˚) around a central point and remain the same. A Ferris wheel and many law enforcement badges are common objects that exhibit rotational symmetry. Objects can be classified by the number of times it matches itself while being rotated. The starfish, for example, has five-fold rotational symmetry because as it is rotated, it will appear to match itself five times.
I ♥ Paraboloids - Poster
PARABOLOID When a parabola is rotated about its axis of symmetry, the three-dimensional surface thus created is a paraboloid. The general equation of a paraboloid in a three-dimensional space is
z=( x 2/ a 2)±( y 2/ b 2)
where a and b are constants. Elliptic paraboloids (in which the terms are added) are used for satellite dishes and in the reflectors in automobile headlights because of the reflective property of a parabola; Pringles potato chips are examples of hyperbolic paraboloids (in which the terms are subtracted).
I ♥ Hyperbolic Cosines - Poster
HYPERBOLIC COSINE Sometimes called the catenary, the hyperbolic cosine is the function whose equation is
=cosh( y )=( x + e x )/2. e - x
The shape of the graph of this function is similar, but not identical, to that of a parabola. To see the difference, students can use their graphing calculators to try to superimpose = cosh ( y x) on the parabola y = x 2 + 1.
While suspension bridges often take the shape of a parabola, any bridge suspended only from its endpoints with uniform weight throughout will take the shape of a catenary or hyperbolic cosine. The Gateway Arch in St. Louis is an inverted catenary slightly flattened at the top, and Antonio Gaudi and other architects have used inverted catenary arches in their buildings.
18" x 24" inches.
I ♥ Oblate Spheroids - Poster
Oblate spheroids are bodies that are shaped like a sphere but are not perfectly round, particularly an ellipsoid, which is generated by revolving an ellipse around one of its axes.
I ♥ Conical Frustums - Poster
I ♥ Conical Frustums - Poster
A conical frustum is formed by slicing the top off a cone. The frustum is what is left. The word frustum comes from the Latin expression for piece or bit.
Star Dancers - Poster
A can be thought of as the set of points formed by connecting the vertices of a regular polygon in a special manner. This poster explores star polygons and discovers some of their properties, arriving at some interesting generalizations. Problems include proving the radian measure of the sum of the interior angles of a given star polygon; making a table that organizes information about the radian measure of interior star polygon angles; and whether or not it is possible to create a human hexagram, heptagram, or octagram. (Solutions provided.)
STAR POLYGON $12.95