Greenwood press

SYMMETRY
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Shoes are reflection-symmetric. The size
and shape of the soles of each shoe match
when they are placed on top of each other.
The cross beams in a kite divide it in
equal pieces and provide support when
the kite is in the air.
The pedals of a flower are rotated around
its center and are evenly spaced apart.

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Some items are constructed to be rotation-symmetric so that they can be use-
ful at multiple angles, or provide an equal distribution. For example, wrenches can
turn bolts at many different positions, and screwdrivers can twist screws continu-
ously. An eggbeater is equally productive at all of its angles when mixing cookie
batter. The blade at the bottom of the lawn mower cuts the grass evenly. A fan
helps circulate air continuously and equally. Playing cards can be held either right-
side up or upside down. A quarterback can throw a smooth spiral to optimize the
distance of a throw because a football is shaped symmetrically. 
An object that is intentionally produced so that it is not rotation-symmetric
sometimes serves a unique purpose, such as that it can only be used in one posi-
tion or does not want its mass distributed equally. For example, a knife is intended
to be held by its handle; a gun can only be fired in one direction; and a pitcher of
water has a handle and lip to provide more support and smoother pouring. 
online sources for further exploration
Frieze patterns

Occupations

Oriental carpets

Symmetry activities

Symmetry and the shape of space

Symmetry around the world project

Symmetry, crystals, and polyhedra

Symmetry in physics

Symmetry point groups

Symmetry project
SYMMETRY/symindex.html>
Types of trusses

Wallpaper groups

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