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Three Dimensional Shapes http://cstl-csm.semo.edu/mcallister/mainpage

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## Three Dimensional Shapes http://cstl-csm.semo.edu/mcallister/mainpage

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**Three Dimensional**Shapeshttp://cstl-csm.semo.edu/mcallister/mainpage Cheryl J. McAllister Southeast Missouri State University MCTM – 2012**While I am talking…**• Select a color(s) of construction paper you like • Select a circle making tool of your choice • Draw circles with at least a 1 inch radius, but no more than a 2 in radius. • You will need at least 4 circles, but 8 will be the best. • You may have to take turns with the tools.**Geometry Standard for Grades Pre-K-2**http://www.nctm.org/standards/content.aspx?id=26846**Geometry Standard for Grades 3-5**http://www.nctm.org/standards/content.aspx?id=26814**Geometry Standard for Grades 6-8**• Instructional programs from prekindergarten through grade 12 should enable all students to— • Analyze characteristics and properties of two- and three-dimensional geometric shapes and develop mathematical arguments about geometric relationships • Expectations: In grades 6–8 all students should— • precisely describe, classify, and understand relationships among types of two- and three-dimensional objects using their defining properties; • understand relationships among the angles, side lengths, perimeters, areas, and volumes of similar objects;**The activity today is one of many, many ways to get students**thinking about and exploring 3-D figures • Can be used to review vocabulary • Can teach students to use construction tools such as compass and straight edge • Can be used to teach some math history • Can be used as an art activity to decorate the classroom**Polyhedron (polyhedra)**• A three dimensional figure composed of polygonal regions (called faces) joined at the sides (edges). The point where edges meet is called a vertex.**Polyhedra are often categorized by their shapes**• Prisms – composed of two bases (which are congruent polygons), joined by parallelograms (called lateral faces). • Pyramids – composed of 1 polygonal base and lateral faces that are triangles that meet at a single point called the apex.**Other info about prisms**• Prisms are often named for the shape of the bases IF the lateral faces are rectangles, then we have a right prism. IF the lateral faces are not rectangles, then we have an oblique prism. • The height (or altitude) of a prism is the perpendicular distance between the bases.**More info about pyramids**• Pyramids are often named by the shape of the base. • The height of a pyramid is the perpendicular distance from the apex to the base. • The slant height of a pyramid is the distance from the apex along a lateral face of the pyramid, perpendicular to the opposite edge of the face. (see next slide)**Height and slant height**h = height s = slant height**More facts about pyramids**• IF the apex is over the center of the base, then the pyramid is a right pyramid, if not, then the pyramid is oblique. • IF the base of the pyramid is a regular polygon, then the pyramid is said to be a regular pyramid.**Height of an oblique pyramid**Note: the height is outside the pyramid**Regular polyhedra (Platonic solids)**Tetrahedron Hexahedron Octahedron Dodecahedron Icosahedron**Extensions of this lesson**• There are only 5 possible regular polyhedra. Can you explain why? • Investigate Euler’s Formula F + V = E + 2**Where to find directions**• http://www.auntannie.com/Geometric/PlatonicSolids/**Another method - Folding nets**• This is what a tetrahedron looks like if you flatten it out.**Thank you!**cjmcallister@semo.edu http://cstl-csm.semo.edu/mcallister/mainpage