Differential Axle
   This differential axle demonstration is in the museum at the University of Mississippi, and is one of a splendid collection of demonstration apparatus assembled at the University in the nineteenth century. The only damage seems to be to the levers at the ends of the shaft, which were originally longer.

   The apparatus can be used in several ways. A mass is attached to a string wound around the axle, and the effects of balancing the resulting torque by pressing on a lever at various distances from the axle can be investigated. Or, strings can be wound in different directions around the two sections of the  axle, and masses hung on their ends to give rotational equilibrium.

   However, I think that this is an example of a Differential Pulley which is used today as a lifting device in automotive and machine shops. The two ends of the string are wound in different directions around the two parts of the axle. A pulley is suspended from the middle of the string. As the axle is turned, this pulley rises or falls slowly, enabling a small force on the lever to lift a large weight. 

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