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Watt's parallel motion on a pumping engine. In previous engines built by Newcomen and Watt, the piston pulled one end of the walking beam downwards during the power stroke using a chain, and the weight of the pump pulled the other end of the beam downwards during the recovery stroke using a second chain, the alternating forces producing the rocking motion of the beam.
In music theory, contrapuntal motion is the general movement of two or more melodic lines with respect to each other. [1] In traditional four-part harmony, it is important that lines maintain their independence, an effect which can be achieved by the judicious use of the four types of contrapuntal motion: parallel motion, similar motion, contrary motion, and oblique motion.
It is similar in this respect to the Chebyshev linkage, a different linkage that produces approximate straight-line motion; however, in the case of Watt's linkage, the motion is perpendicular to the line between its two endpoints, whereas in the Chebyshev linkage the motion is parallel to this line.
Straight-line motion is linear motion of definite length or "stroke", every forward stroke being followed by a return stroke, giving reciprocating motion. The first such mechanism, patented in 1784 by James Watt, produced approximate straight-line motion, referred to by Watt as parallel motion.
In the example on the top right, we see a series of quartal chords in parallel motion, in which the intervallic relationship between each consecutive chord member, in this case a minor second, is consistent. Each note in the chord falls by one semitone in each step, from F, B ♭, and E ♭ in the first chord to D, G, and C in the last
James Watt's parallel motion and Watt's linkage; Peaucellier–Lipkin linkage, the first planar linkage to create a perfect straight line output from rotary input; eight-bar, one DOF. A Scott Russell linkage, which converts linear motion, to (almost) linear motion in a line perpendicular to the input.
Parallelogram (Parallel Motion [Note 2]) and Antiparallelogram (Contraparallelogram, Inverse Parallelogram, Butterfly, Bow-tie) linkages; Deltoid (Galloway) and Trapezium (Arglin) linkages; Three revolute joints: It is denoted as RRRP, PRRR, RPRR, or RRPR, constructed from four links connected by three revolute joints and one prismatic joint.
"The reason for avoiding parallel 5ths and 8ves has to do with the nature of counterpoint. The P8 and P5 are the most stable of intervals, and to link two voices through parallel motion at such intervals interferes with their independence much more than would parallel motion at 3rds or 6ths."