Question

Understanding Torsion Help?
With this question:

http://img339.imageshack.us/img339/9807/capturekaz.png

how do I know which gears act on section 3? All of these type questions seem to be unpredictable of which gears act on a particular section.

Why isn't gear C acting on section 3 even though the right hand rule is pointing in the section 3 direction?

Also I would like to know what gears act on for sections for 1, 2 and 4.

Thanks in advance!

Answer 1

It doesn't matter which end of the shaft you start at, but if you start at the motor end, realize that the motor exerts a moment such that the shaft is in equilibrium and not moving. If you work from the free end, you don't have to find the torque exerted by the motor.

The direction you work through the beam determined which gears act on each section. From the free end, for section 3, both gears E and D act on that section. If you go from the motor end, the motor and gears B and C will act on section 3.

Work it from both ways and you'll be pleasantly surprised that you get the same answers.