Scissors are hand-operated cutting instruments. They consist of a pair of metal blades pivoted so that the sharpened edges slide against each other when the handles (bows) opposite to the pivot are closed. Scissors are used for cutting various thin materials, such as paper, cardboard, metal foil, thin plastic, cloth, rope and wire. Scissors can also be used to cut hair and food. Scissors and shears are functionally equivalent, but larger implements tend to be called shears.
A pair of scissors consists of two pivoted blades. In lower quality scissors the cutting edges are not particularly sharp; it is primarily the shearing action between the two blades that cuts the material. In high quality scissors the blades can be both extremely sharp, and tension sprung - to increase the cutting and shearing tension only at the exact point where the blades meet. The hand movement (pushing with the thumb, pulling with the fingers in right handed use) can add to this tension. An ideal example is in high quality tailors scissors or shears, which need to be able perfectly cut (and not simply tear apart) delicate cloths such as chiffon and silk.
Mechanically, scissors are a first-class double-lever with the pivot acting as the fulcrum. For cutting thick or heavy material, the mechanical advantage of a lever can be exploited by placing the material to be cut as close to the fulcrum as possible. For example, if the applied force (i.e., the hand) is twice as far away from the fulcrum as the cutting location (e.g., piece of paper), the force at the cutting location is twice that of the applied force at the handles. Scissors cut material by applying a local shear stress at the cutting location which exceeds the material's shear strength.
The consumer is responsible for maintaining the quality of the scissors. Scissors should only be used to cut the materials for which they were designed. They should be oiled and sharpened regularly, and the screw should be adjusted as necessary. Scissors should be stored in a closed position. Setting down scissors in an open position is the most common cause of dull blades.
