## Friday, November 19, 2010

### Arithmetical Words, Part V

We have come to the end of the arithmetic alphabet with R-Z today. Most of the time this blog deals with using math in real life, but without knowing math words, it's hard to communicate precisely.

We tend to say square or rectangular when we are talking about 3D objects, even when we mean rectangular prism. I was talking with my friend Chris, who said he was putting square gabions in his back yard. I knew the word gabion meant a big wire cage, but I didn't know what shape they might be. I learned gabions can be purchased as rectangular prisms, cylinders or cubes. You put them in place, then fill them with heavy material to form earthen walls.

If we want to be extra-precise, gabions aren't solid figures until they unfolded and filled. Here are some pictures of his empty ones, waiting for 2 tons of dirt. We'll do the math calculations on the dirt in another blog:

Now, on to the definitions:
• Radius straight line from the center point of a circle to any point on the circle
• Ray line with one endpoint
• Rectangular Prism solid figure with 8 vertices, 12 straight edges and a total of 6 rectangular flat faces, one of which is the base
• Rectangular Pyramid solid figure with 5 vertices, 8 straight edges, 4 triangular flat faces and 1 rectangular base
• Reflection movement of a figure over a line that results in a mirror image; a Flip
• Remainder amount left over when one number is divided by another
• Right Angle angle that measures exactly 90 degrees
• Roman Numerals number system created by ancient Romans that uses letters rather than numerals; not based on place value
• Rotate to move or turn a figure around a point; a Turn
• Round (1) a circular or cylindrical shape
• Round (2) replacing an exact number with an approximate number that is more convenient to use
• Scalene Triangle a triangle where all three sides are of different lengths
• Similar Figures figures having the same proportions but not the same size
• Slide when a figure moves without changing its appearance, see translation
• Sphere 3D solid figure where all points on the surface are equidistant from the center
• Square 2D parallelogram with 4 congruent sides and 4 congruent angles
• Square Pyramid 3D solid figure with a total of 5 vertices, 8 straight edges, 4 triangular faces and a square base
• Square units (1) group of squares with sides one unit in length, which are laid on top of an object to measure its area
• Square units (2) a unit of distance when multiplied by itself becomes a measure of area
• Surface area the sum of the areas of all the faces of a three-dimensional figure
• Three-Dimensional Figures 3D geometric objects with length, width and height; they are “solid”
• Translation when a figure moves without changing its appearance, see slide.
• Triangular Prism 3D figure with 6 vertices, 6 straight edges, 3 rectangular flat faces and 2 triangular flat faces
• Triangular Pyramid 3D figure with 4 vertices, 6 straight edges, and 4 triangular flat faces
• Turn to make a figure revolve around a point, Rotate
• Two-Dimensional Figures 2D geometric objects with only length and width; they are “flat”
• Vertex point where at least two straight lines meet (flat figures) or three straight edges meet (solid figures); plural is vertices
• Volume measurement of the amount of space occupied by material; expressed in cubic units
• Week period of time consisting of 7 days; not related to solar or lunar activity
• Weight measurement that describes how heavy an object is; due to earth's gravity
• Yard unit of length equalling 3 feet; 36 inches; .9 meters
• Year time period of 365-366 days or 12 months; based on rotation of Earth around the sun
• Zero Property: Addition any number added to zero has itself as the sum
• Zero Property: Multiplication any number multiplied by zero has a product of zero