How Is Pottery Throwing Clay an Example of Friction?
Potters throwing clay on a potter's wheel use the forces of physics to shape the clay as it spins. Friction is the main force driving the adaptation of clay in the hands of the potter. There are two main forces of friction that develop when throwing clay: hands on clay friction and flywheel generated friction. Hands on clay friction deals with the friction generated as the potter compresses the clay while it spins through his hands. Flywheel friction is generated from a kick wheel model that uses a large circular weight or flywheel under the shaft to support the wheel head for throwing.
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History
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The invention of the turntable for the production of pottery dates back to around 3000 BC. By 2500 BC, the Egyptians were recording their use of the turntable made from wood and stone on tomb walls. The earliest Egyptian turntables were only rotation stands for coil built pottery. The turntable evolved through many cultures over the centuries until it became the momentum wheel in the 16th century. This form consisted of a wheel head where the clay could be formed, a flywheel that could be spun with the feet to produce momentum and a shaft to connect the two. The modern electric motor potter's wheel was developed during the industrial revolution to speed up the production of pottery on a large scale.
Features
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A kick wheel's wheel head is connected to the central shaft. The shaft is attached to the heavy flywheel, or kick wheel near the floor. The three part machine is housed in a simple frame that holds the shaft loosely allowing it to spin as the potter kicks the bottom flywheel. This kinetic energy produces rotation for the upper wheel head. Because of the kick wheel's weight, potential energy is also accumulated in the flywheel, which helps it spin much longer and with more force without the constant kick of the potter.
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Types
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The 16th century Italian potter's wheel used polished stone or glass for the axis to keep the shaft and kick wheel off the floor and a greased strip of leather as a bearing to allow the shaft to rotate freely inside the frame. By the 19th century, the French had developed a potter's wheel that used greased metal parts and bearings. The modern electric wheel uses a motor driven central shaft and greased modern bearings.
Friction Levels
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The earliest Egyptian wheels produced massive friction when spun due to the wheel head's shaft being supported by crudely cut wood or stone housing. The innovation of later wheels helped reduce friction with polished glass, metals and greased bearings. The modern, motor driven potter's wheel produces very little friction in the machine itself. Most of the friction comes from the potter's hands as they attempt to coax the clay into a vertical form.
Prevention/Solution
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The use of grease for all metal joints and liberally applied water to the clay while the potter is working are two ways to lessen the amount of friction produced by the wheel's turning.
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References
Resources
- Photo Credit pottery image by Dubravko Grakalic from Fotolia.com
