Observe the Deformation  
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Diagram shows two vertical shafts A B marked 1 and C D marked 2 centered on the x and x prime axes respectively. A gear of 150 millimeter diameter is at A on shaft 1 at a height of 400 millimeters. A gear of 100 millimeter diameter is at C on shaft 2 at a height of 400 millimeters. Above the gear A a torque T is applied on shaft 1 in the counterclockwise direction. There is an inward twist on the shafts 1 and 2.

The dark lines drawn on each shaft are meant to help you visualize the twisting in each shaft as the gears rotate. Let's look at the deformation one more time. This time watch the gears.