Glossary - P
Parallel circuit. A circuit in which two or more electrical resistances or loads are connected across the same voltage source.
Pascalís Law. The law that states that pressure applied anywhere to a body of fluid causes a force to be transmitted equally in all directions; the force acts at right angles to any surface in contact with the fluid.
Percentage. Used to express a number as a fraction of 100. Using the percentage sign, %, 90 percent is expressed as 90%.
Permeability. Used to refer to the ease with which a magnetic flux can be established in a given magnetic circuit.
Perspective view. A drawing that shows a three-dimensional object (portraying height, width, and depth) as it appears to an observer. It most closely resembles the way an object would look in a photograph.
Phantom line. Composed of one long and two short evenly spaced dashes, indicates an alternate position of parts of the object or the relative position of a missing part.
Pictorial drawing. A drawing that is similar to a photograph. It shows an object as it appears to the eye, but it is not satisfactory for showing complex forms and shapes.
Pitch. Term used to describe the frequency of a sound.
Plumb bob. A heavy metal object, cylinder- or coneshaped, with a sharp point at one end that is suspended by a string to produce a vertical reference line useful in aircraft measurements.
Positive number. A number that is greater than zero.
Potential difference. A difference in electrical pressure.
Potential energy. Energy that is stored.
Potentiometer. A variable tapped resistor that can be used as a voltage divider.
Power (exponent). A shorthand method of indicating how many times a number, called the base, is multiplied by itself. For example, in the number 43, 3 is the power, or exponent, and 4 is the base. That is, 43 is equal to 4 ◊ 4 ◊ 4 = 64.
Power. Power is the time rate at which work is done or energy is transferred.
Powers of ten. Also called scientific notation. It is a shorthand method of depicting very large or very small numbers.
Pressure. The amount of force acting on a specific amount of surface area, typically measured in pounds per square inch or psi.
Preventive maintenance. Simple or minor preservation operations and the replacement of small standard parts not involving complex assembly operations.
Product. The result of multiplication.
Progressive inspection. Breaking down the large task of conducting a major inspection into smaller tasks which can be accomplished periodically without taking the aircraft out of service for an extended period of time.
Proportion. A proportion is a statement of equality between two or more ratios. The example of A is to B as C is to D can be represented A:B = C:D or A/B = C/D.
Pythagorean Theorem. An equation used to find the length of a third side of any right triangle when the lengths of two sides are known. The Pythagorean Theorem states that a2 + b2 = c2. The square of the hypotenuse (side opposite the right angle) is equal to the sum of the squares of the other two sides (a and b).
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