Wheel throwing is one general form of pottery, the first step being the centering of the clay to the wheel.
Three main forces are applied to keep the clay in place and directly in the center of the wheel. A force from the top and side push the clay down and into the wheel,
 and a normal force is present as well that pushes against the weight of the clay. From there the clay is pulled upwards with equal and opposite pressure from both sides
before continuing the centering process by repeating the initial steps.
centering clay
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