Persistent. Keeping at it; determination to proceed.
Perpendicular. At right angles to a surface. This term is sometimes wrongly applied in referring to an object, particularly to an object which is vertical, meaning up and down. The blade of a square is perpendieular to the handle at all times, but the blade is vertical only when it points to the center of the earth.
Pernicious. Bad; not having good features or possessing wrong attributes.
Pendulum. A bar or body suspended at a point and adapted to swing to and fro.
Perpetual. For all time; unending or unlimited time.
Phenomena. Some peculiar happening, or event, or object.
Pitch. In aviation this applies to the angle at which the blades of a propeller are cut. If a propeller is turned, and it moves forwardly in the exact path made by the angle, for one complete turn, the distance traveled by the propeller axially indicates the pitch in feet.
Placement. When an object is located at any particular point, so that it is operative the location is called the placement.
Plane. A flat surface for supporting a flying machine in the air. Plane of movement pertains to the imaginary surface described by a moving body. A bicycle wheel, for instance, when moving forwardly in a straight line, has a plane of movement which is vertical; but when the machine turns in a circle the upper end of the wheel is turned inwardly, and the plane of rhovement is at an angle.
Pliant. Easily yielding; capable of being bent; liable to be put out of shape.