Greenwood press
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book-20600
SYMMETRY
139 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. 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 Types of trusses Wallpaper groups ▲ ▼ ▲ Download 1.81 Mb. Do'stlaringiz bilan baham: |
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