About FORCE and TORQUE...?

Question

Based on a physics textbook, TORQUE is defined as a cross product between Force and Distance (T = F x D).

Scenario:
Given: a circular disc with a radius of 2 feet that is connected to a shaft (making them a single unit).

Question:
If the shaft is rotated with a Force of 10 pounds, and the edge of the disc is attached to another another disc with a similar shaft, what would be the output torque? 20 lb-ft? Please explain.

A simple illustration below. The figure represents the 2 discs with shafts (face opposite each other).

Force 10 lbs... --[ ]-- ...Torque at the other end?


Many thanks!

Answer 1

You could just as well take the disks off and weld the 2 shafts together.

You should say what torque you are applying, or you should say via what lever arm you are applying 10 lb force. If you apply 10 ft-lbs of torque to the left side, you will get 10 ft-lbs at the right.

If you apply 10 lbs to the surface of the shaft, and it has a radius of 0.1 feet, you are applying 10 lbs*0.1 feet or 1 ft-lb. And that's the torque you get at the other end.

If you take the driven disk and have the surface of of the disk drive the other part's axel, then you get a transformation of torque.

Answer 2

♦ no; the system will transmit the same torque throughout the whole axel not taking friction into account; in other words if you apply force of 10 lb on axel, say with radius r=1 inch of the left-hand shaft, you’ll be able to lift a load of 10 lb with a rope wound around the right-hand shaft provided its radius being the same 1 inch;
♦ be the radius of the right-hand shaft 2 times greater you’ll be able to lift a load of 5 lb only – see your formula.