Show Gear Rotations  
scene 11 of 12
The angular displacement on gear with 100 millimeter diameter is phi subscript B. The angular displacement on gear with 200 millimeter diameter is phi subscript C. The angular displacement of shaft C D is phi subscript 2. A torque T in counter clockwise direction is applied on the shaft at D.

Let's review the rotations in the system, looking from another viewpoint:

Since shaft (2) is connected to gear C, the entire shaft rotates along with the gear.

The positive torque T2 in shaft (2) causes the shaft to twist counterclockwise an additional angle of φ2 between gear C and point D.