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A helix is a curved line formed by a point rotating around a center while the center moves up or down the z-axis. Helices are either right or left handed with curled fingers giving the direction of rotation and thumb giving the direction of advance along the z-axis. The threads of a screw are helical and therefore screws can be right- or left ...
Two-dimensional rotation can occur in two possible directions or senses of rotation.Clockwise motion (abbreviated CW) proceeds in the same direction as a clock's hands relative to the observer: from the top to the right, then down and then to the left, and back up to the top.
In these dances the follower's right arm is normally used to lead a turn (most commonly by the leader's left arm, but sometimes by the leader's right arm when a cross-hand or "handshake" position is used), an inside turn is normally a left (counter-clockwise) turn, while an outside turn is a right (clockwise) turn.
This corresponds to a counterclockwise twist for the right forearm and a clockwise twist for the left (when viewed superiorly). In the forearm, this action is performed by pronator quadratus and pronator teres muscle .
The numbers on left-handed rulers move from right to left so lefties can see them clearly as they move their pens. When you hold a tape measure in your left hand, the numbers are upside down.
Movement is sinistral (left-handed) if the block on the other side of the fault moves to the left, or if straddling the fault the left side moves toward the observer. Movement is dextral (right-handed) if the block on the other side of the fault moves to the right, or if straddling the fault the right side moves toward the observer. [4]
So a standard clock, with its spin vector defined by the rotation of its hands, has left-handed helicity if tossed with its face directed forwards. Mathematically, helicity is the sign of the projection of the spin vector onto the momentum vector : "left" is negative, "right" is positive.
If a standard right-handed Cartesian coordinate system is used, with the x-axis to the right and the y-axis up, the rotation R(θ) is counterclockwise. If a left-handed Cartesian coordinate system is used, with x directed to the right but y directed down, R(θ) is clockwise.