Digits, Grade 8, Volume 1, Homework Helper

### 5-5: Volumes of Spheres

#### Key Concept

The volume of a sphere is the number of unit cubes, or cubic units, needed to fill the sphere.

You can find the formula for the volume of a sphere by comparing it with the volume of a cylinder with a height and diameter equal to the diameter of the sphere. Fill the cylinder with water up to the 1 third mark.

Drop the sphere in the cylinder. When the sphere is completely submerged, the water level reaches the top of the cylinder. Use the formula V = πr 2 h to find the volume of the cylinder. The formula for the volume of this cylinder is V = 2πr 3.

The sphere filled two-thirds of the space in the cylinder.

table with 3 rows and 2 columns , row1 column 1 , cap volumeofthesphere , column 2 equals , 2 thirds , open . cap volumeofthecylinder . close , row2 column 1 , , column 2 equals , 2 thirds , open 2 pi , r super 3 end super , close , row3 column 1 , , column 2 equals , 4 thirds , pi r , end table

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