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Volumes of Rectangular Prisms and Cylinders. Lesson 9-9. Vocabulary. The volume of a three-dimensional figure is the number of cubic units needed to fill the space inside the figure. A cubic unit is a cube that measures 1 unit long, 1 unit wide, and 1 unit high. Counting Cubes.
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Volumes of Rectangular Prisms and Cylinders Lesson 9-9
Vocabulary • The volume of a three-dimensional figure is the number of cubic units needed to fill the space inside the figure. • A cubic unit is a cube that measures 1 unit long, 1 unit wide, and 1 unit high.
Counting Cubes • If the figure is split into cubes already, then just count the cubes in one layer and multiply that by the number of layers. The top layer is 4 x 5, or 20 cubic units. There are 20 cubic units per layer, times 3 layers, for a volume of 60 cubic units.
Using Formulas • To find the volume of a rectangular prism or a cylinder, multiply the area of the base by the height. • Volume = Area of Base x height • V = Bh • (The capital B does not stand for base, it stands for area of the base.)
Volume of a Rectangular Prism V = Bh In this case, the base is a rectangle. The area formula for a rectangle is l x w. V = (l x w) x h V = (4 x 3) x 12 V = 144 cm3 Volume gives us cubic units.
Volume of a Cylinder V = Bh In this case, the base is a circle. The area formula for a circle is r2 5 in 16 in V = (r2) x h V = (3.14)(52)(16) V = (3.14)(25)(16) V = 1,256 in3
Homework Time V = l w h