The Physics
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Speed of a Phonograph Record

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Bibliographic Entry Result
(w/surrounding text)
Cutnell & Johnson. Physics.3rd ed. New York: Wiley, 1995: 155 (problem 18). "What is the minimum coefficient of static friction necessary to allow a penny to rotate along with a 33 1/3 rpm record. (Diameter = 0.300 m)When the penny is placed at the outer edge of the record." 0.53 m/s
(12" LP)
World Book Encyclopedia Millennium Edition. Chicago: World Book, 2000. "The DJ disk (Wheel of Steel). It is played at a speed of 45 revolutions per minute (45 rpm). A 12 inch record at 33 1/3. Diameter = 12 inches." 0.42 m/s
(7" single)
Gallagher, Hugh. "The Wheel of Steel." Rolling Stone Technology. (27 November 1997): 97-99. "It gives a quick start. It may reach up to 33 1/3 rpm within 0.7 s. This means that it is able to make a quiet room turn to a party house." 0.53 m/s
(12" LP)
Oliver Reed & Walter L. Welch. From Tin Foil to Stereo. Indianapolis, IN: Howard W. Sams, 1959. "More costly 78 rpm Shellac and plastic disks, as well as over the 10 and 12 inch 33 1/3 rpm discs with their preselected repertoire, 0.7 in 33 1/3 rpm. 45 rpm will serve the best." 1.04 m/s
(10" 78 rpm)
Cutting Specs. Aardvark Record Mastering. "12"at 33 rpm, max time at 0 db, 20 mins.
12"at 33 rpm, max time at -3 db, 24 mins.
12"at 33 rpm, max time at -6 db, 28 mins.
7"at 45 rpm, max time at +3 db, 4 mins.
7"at 45 rpm, max time at 0 db, 5 mins.
7"at 45 rpm, max time at -3 db, 6 mins.
7"at 33 rpm, max time at 0 db, 6-1/2 mins.
Not Suggested due to distortion potential.
7"at 33 rpm, max time at -3 db, 7-1/2 mins.
7"at 33 rpm, max time at -6 db, 9-1/2 mins."
0.53 m/s
(12" LP)
0.42 m/s
(7" single)

A phonograph is a device that is able to make sounds that was recorded on phonograph records. Up until the mid 1980s it was the most popular recorded medium. It gave the people entertainment. Thomas A. Edison invented the first phonograph in 1877. The phonograph was tin foil that was wrapped around a small metal cylinder, and was able to record sound. The vibrations of a cutting needle record sound.

Many phonographs records were thin plastic discs with a diameter of 7, 10, or 12 inches (18, 25, or 30 cm). A 7 inch single is normally played at 45 revolutions per minute (rpm). A 12 inch long-playing record (LP) is normally played at 33 1/3 rpm. Old-fashioned 10 inch records were played at 78 rpm. There has been much change for the speeds of the phonograph. Due to the evolution of the way people think. An LP is able to hold about 30 minutes of sound per side.

In this essay, we are concerned with the linear speed; that is, v.

v = s /t or 2*pi*r/T

Where s is displacement, t is time, r is radius, and T is period. Since we have the diameters of the records in inches we need to convert them to the radius in meters. The period is 60 seconds divided by the number of rpm's.

For example: a 78 rpm record with a 10 in diameter

V = 2*pi*(05 in)(.0254 m/in)(78 rpm)/(60 s/min) = 1.04 m/s

Anny Peng -- 2001