Greenwood press

138
SYMMETRY
The wings of butterflies are reflection-
symmetric with their bodies.

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than the other. However, shoes are manufactured to be symmetrical because the
same foot is not larger on every person nor is the larger foot uniformly larger
among people. Hence, one foot may have a tighter fit in one of the shoes.
Some objects are designed to be reflection-symmetric so that they can bal-
ance and have more support. For example, airplane engines and wheels are
placed equidistant from the fuselage to divide equally their mass and power. Cer-
tain merchandise might be intentionally built not to be reflection-symmetric if it
is customized to meet a person’s needs. For instance, scissors are made especial-
ly for right-handed or left-handed people. A left-handed person will find it more
difficult cutting with a right-handed pair of scissors.
Many kites are reflection-symmetric, because they have a cross beam that is
a perpendicular bisector of the other cross beam, as shown in the following fig-
ure. The perpendicular bisector then becomes a line of symmetry that divides the
kite into two equal pieces.
An object is rotation-symmetric if one of its pieces can be rotated around a
point so that it is congruent with its other piece(s). For example, some flowers
are rotation-symmetric, because their pedals are uniformly distributed, as shown
below.