[MUSIC] Welcome back to mechanics of materials part two. This is module nine, and we've been moving right along in the course. And so we finished the section on thin-walled pressure vessels, and today we start the topic of torsion. So the learning outcomes for today are to define the torsional loading of engineering structures and to give some examples of real world torsional engineering applications. So torsional loading of engineering structures is when we twist the object due to an applied torque for moment and the units for torsion are Newton-meters or foot-pounds. And so, here's a member being twisted with a torque at both ends, and here is the original line on the member, and when we torque it, it turns, and I've exaggerated this turning. You can see this on my demo here. I have this engineering member and if I apply a torque or a moment, you can see how it twists and turns. And so, this is a material that has a very low stiffness and so we can see the deformations very easily. This is a pool noodle. Okay, so let's look at some examples of when we would use torsional loading of engineering structures. One would be torsional bar suspension systems. And here's a race car and you can see here as the suspension system goes up and down, this is a member here that would be loaded with torsion, the same down here. As this is twisted, there would be a torsional load placed on this engineering member. Another example, this is a track vehicle. Again, it's a suspension system. As this roller wheel goes up and down then it's going to produce a torque on this member here that goes back into the body of the track vehicle. Another example would be turbines. Here is an example of a turbine. Through the middle of this turbine there's a shaft and that shaft is exposed to torsional loading. Also wind turbines, there's shafts up here on the wind turbine, which as the wind turbine operates are subjected to torsional loading. And finally, you even see examples of torsion in, for instance, bone spiral fractures in biomechanics. And so, as an example, again, if I have my arm here and this bone, if it gets twisted and breaks, you get a fracture, and that's a bone spiral fracture due to a torsional loading. And then one final real world example is this driveshaft. This is, again, a driveshaft from a mini-baja vehicle, which is a project that we do each year in the mechanical engineering school here at Georgia Tech. The students have a team that put together a mini-baja or kind of a dune buggy vehicle, and this is the driveshaft that was taken out of one of those members and it's subjected to torsional loading. And so those are all good examples, of when you, real world examples, when you would see torsional loading of engineering structures. And we'll go on and do the theory as we start the next module. [SOUND]