A sphere 
is a set of
points in three dimensional space equidistant from a point called the
center of the sphere.
The distance from the center to the
points on the sphere is called the radius
of the sphere.
Notice that we are talking about the surface of a ball, and not the
ball itself. The surface of the
earth we live on is a good approximation to a sphere. As you read
through this material it would be helpful to have a beach ball about 12''
in diameter with a smooth, solid colored surface, a marking pen,
preferably the kind that easily washes off, string, scissors, and a
protractor. All points on the surface are the same distance from the centre. It has no edges or vertices (corners).
is a set of
points in three dimensional space equidistant from a point called the
center of the sphere.
The distance from the center to the
points on the sphere is called the radius
of the sphere.
Notice that we are talking about the surface of a ball, and not the
ball itself. The surface of the
earth we live on is a good approximation to a sphere. As you read
through this material it would be helpful to have a beach ball about 12''
in diameter with a smooth, solid colored surface, a marking pen,
preferably the kind that easily washes off, string, scissors, and a
protractor. All points on the surface are the same distance from the centre. It has no edges or vertices (corners).
Volume = (4/3) × π ×r
Surface Area = 4× π × r23
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