# Math Geometry Terms for Fifth Grade

by Susan Rickey

Much of the focus in fifth-grade math centers on correctly doing operations with fractions and decimals. Students learn to perform addition, subtraction and multiplication of whole numbers as well as fractions and decimals. Even though the focus is on rational numbers, geometry is also a part of the math curriculum for fifth-grade students.

## Two-Dimensional Polygons

Children learn names of two-dimensional polygons and how to identify the polygons by their properties. Polygons are classified by the number of sides they have -- such as quadrilateral, pentagon, hexagon and octagon. They are also sorted and named by the number and type of angles, such as triangle and quadrangle. Students in fifth grade learn to understand parallel lines. A parallelogram, such as a square or rectangle, has two pairs of lines that are parallel to each other. Show the children a map of the local town. Ask students to highlight lines that are parallel to each other. Give them a different highlighter and ask them to mark perpendicular lines. Call out the name of a street. Roll the dice -- an odd roll means they find a street that is perpendicular to the first one you called out. An even roll means they find a parallel street.

## Three-Dimensional Shapes

Fifth-grade students recognize the terms associated with finding the volume of a rectangular prism. A rectangular prism has six faces, or sides. It has 12 edges -- line segments where the faces meet. It has eight vertices -- points where lines meet. Bring in cereal, pizza and cracker boxes to find the volume of these rectangular prisms. The students will learn how to find the length, width and height of the prism to calculate its volume.

## Angles

Students know the terms associated with identifying angles. Angles are sorted by the degrees they possess, or the size of the opening. A right angle is 90 degrees, an acute angle is less than 90 degrees and an obtuse angle is between 91 and 179 degrees. A straight angle makes a straight line and is 180 degrees. A reflex angle is more than 180 degrees and less than 360. When naming right, acute, obtuse, straight and reflex angles in a polygon, have students identify the properties of polygons. One difference between an irregular and a regular polygon is the size of the polygon's angles. A regular polygon has the same size angles. An irregular polygon has angles that differ in size.

## Coordinate Plane

Understanding the coordinate plane is a part of a fifth-grade student's math year. The terms associated with this pair of lines arranged perpendicularly help students locate points in four quadrants made by the lines. The point where the lines meet is called the origin, and it is defined by a "0." The lines are each called an axis. Coordinates are numbers that indicate how far along each of the lines travel.