Accounting for Gear Rotation  
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Diagram shows two shafts A B and C D of 35 millimeter diameter and 300 millimeter and 900 millimeter respectively, are connected using two gears, B with 100 millimeter diameter and C with 200 millimeter diameter. The angular displacement on gear with 100 millimeter diameter is phi subscript B. A torque T is applied at the end of C D at D. Parameters: d = 35 millimeter, G = 80 gega Pascal, T = 685 Newton meter.

Gear C and gear B are connected by the gear teeth. When the gears rotate, they both turn through the same arclength (since the teeth have to be the same size for the gears to mesh properly).