Spheres

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10-8
Spheres
Warm Up
Lesson Presentation
Lesson Quiz
Holt Geometry
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Warm Up Find each measurement. 1. the radius of
circle M if the diameter is 25 cm 2. the
circumference of circle X if the radius is 42.5
in. 3. the area of circle T if the diameter is
26 ft 4. the circumference of circle N if the
area is 625? cm2
12.5 cm
85? in.
169? ft2
50? cm
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Objectives
Learn and apply the formula for the volume of a
sphere. Learn and apply the formula for the
surface area of a sphere.
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Vocabulary
sphere center of a sphere radius of a
sphere hemisphere great circle
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A sphere is the locus of points in space that are
a fixed distance from a given point called the
center of a sphere. A radius of a sphere connects
the center of the sphere to any point on the
sphere. A hemisphere is half of a sphere. A great
circle divides a sphere into two hemispheres
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The figure shows a hemisphere and a cylinder with
a cone removed from its interior. The cross
sections have the same area at every level, so
the volumes are equal by Cavalieris Principle.
You will prove that the cross sections have equal
areas in Exercise 39.
The height of the hemisphere is equal to the
radius.
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V(hemisphere) V(cylinder) V(cone)
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Example 1A Finding Volumes of Spheres
Find the volume of the sphere. Give your answer
in terms of ?.
Volume of a sphere.
2304? in3
Simplify.
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Example 1B Finding Volumes of Spheres
Find the diameter of a sphere with volume 36,000?
cm3.
Volume of a sphere.
Substitute 36,000? for V.
27,000 r3
r 30
Take the cube root of both sides.
d 60 cm
d 2r
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Example 1C Finding Volumes of Spheres
Find the volume of the hemisphere.
Volume of a hemisphere
Substitute 15 for r.
2250? m3
Simplify.
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Check It Out! Example 1
Find the radius of a sphere with volume 2304? ft3.
Volume of a sphere
Substitute for V.
r 12 ft
Simplify.
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Example 2 Sports Application
A sporting goods store sells exercise balls in
two sizes, standard (22-in. diameter) and jumbo
(34-in. diameter). How many times as great is the
volume of a jumbo ball as the volume of a
standard ball?
jumbo ball
standard ball
A jumbo ball is about 3.7 times as great in
volume as a standard ball.
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Check It Out! Example 2
A hummingbird eyeball has a diameter of
approximately 0.6 cm. How many times as great is
the volume of a human eyeball as the volume of a
hummingbird eyeball?
hummingbird
human
The human eyeball is about 72.3 times as great in
volume as a hummingbird eyeball.
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In the figure, the vertex of the pyramid is at
the center of the sphere. The height of the
pyramid is approximately the radius r of the
sphere. Suppose the entire sphere is filled with
n pyramids that each have base area B and height
r.
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4?r2 nB
If the pyramids fill the sphere, the total area
of the bases is approximately equal to the
surface area of the sphere S, so 4?r2 S. As the
number of pyramids increases, the approximation
gets closer to the actual surface area.
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Example 3A Finding Surface Area of Spheres
Find the surface area of a sphere with diameter
76 cm. Give your answers in terms of ?.
S 4?r2
Surface area of a sphere
S 4?(38)2 5776? cm2
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Example 3B Finding Surface Area of Spheres
Find the volume of a sphere with surface area
324? in2. Give your answers in terms of ?.
S 4?r2
Surface area of a sphere
Substitute 324? for S.
324? 4?r2
r 9
Solve for r.
Substitute 9 for r.
The volume of the sphere is 972? in2.
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Example 3C Finding Surface Area of Spheres
Find the surface area of a sphere with a great
circle that has an area of 49? mi2.
A ?r2
Area of a circle
Substitute 49? for A.
49? ?r2
r 7
Solve for r.
S 4?r2
4?(7)2 196? mi2
Substitute 7 for r.
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Check It Out! Example 3
Find the surface area of the sphere.
S 4?r2
Surface area of a sphere
Substitute 25 for r.
S 4?(25)2
S 2500? cm2
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Example 4 Exploring Effects of Changing
Dimensions
The radius of the sphere is multiplied by .
Describe the effect on the volume.
original dimensions
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Check It Out! Example 4
The radius of the sphere is divided by 3.
Describe the effect on the surface area.
original dimensions
dimensions divided by 3
S 4?r2
S 4?r2
4?(3)2 36? m3
4?(1)2 4? m3
The surface area is divided by 9.
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Example 5 Finding Surface Areas and Volumes of
Composite Figures
Find the surface area and volume of the composite
figure. Give your answer in terms of ?.
Step 1 Find the surface area of the composite
figure.
The surface area of the composite figure is the
sum of the curved surface area of the hemisphere,
the lateral area of the cylinder, and the base
area of the cylinder.
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Example 5 Continued
Find the surface area and volume of the composite
figure. Give your answer in terms of ?.
L(cylinder) 2?rh 2?(6)(9) 108? in2
B(cylinder) ?r2 ?(6)2 36? in2
The surface area of the composite figure is
72? 108? 36? 216? in2.
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Example 5 Continued
Find the surface area and volume of the composite
figure. Give your answer in terms of ?.
Step 2 Find the volume of the composite figure.
The volume of the composite figure is the sum of
the volume of the hemisphere and the volume of
the cylinder.
The volume of the composite figure is 144? 324?
468? in3.
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Check It Out! Example 5
Find the surface area and volume of the composite
figure.
Step 1 Find the surface area of the composite
figure.
The surface area of the composite figure is the
sum of the curved surface area of the hemisphere,
the lateral area of the cylinder, and the base
area of the cylinder.
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Check It Out! Example 5 Continued
Find the surface area and volume of the composite
figure.
L(cylinder) 2?rh 2?(3)(5) 30? ft2
B(cylinder) ?r2 ?(3)2 9? ft2
The surface area of the composite figure is
18? 30? 9? 57? ft2.
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Check It Out! Example 5 Continued
Find the surface area and volume of the composite
figure.
Step 2 Find the volume of the composite figure.
The volume of the composite figure is the volume
of the cylinder minus the volume of the
hemisphere.
V 45? 18? 27? ft3
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Lesson Quiz Part I
Find each measurement. Give your answers in terms
of ?. 1. the volume and surface area of the
sphere 2. the volume and surface area of a
sphere with great circle area 36? in2 3. the
volume and surface area of the hemisphere
V 36? cm3 S 36? cm2
V 288? in3 S 144? in2
V 23,958? ft3 S 3267? ft2
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Lesson Quiz Part II
4. A sphere has radius 4. If the radius is
multiplied by 5, describe what happens to the
surface area. 5. Find the volume and surface
area of the composite figure. Give your answer
in terms of ?.
The surface area is multiplied by 25.
V 522? ft3 S 267? ft2