 Welcome back MechanicalEI, did you know that torsion is what makes your car move and keeps your head from turning 360 degrees? This makes us wonder, what is torsion? Before we jump in, check out the previous part of this series to learn about how shear stress is distributed. Now, torsion is a twisting of an object due to an applied torque. It is expressed in Newtons per square meter Pascals or Pound per square inch PSI. For shafts of uniform cross section, the torsion T is given by the product of torsion constant JT and maximum shear stress tau divided by the distance between the rotational axis and the autosurface R. The maximum shear stress value for a solid shaft of diameter D with torque T applied to it is given by Tmax equals 16T upon pi D cubed. The same value for a hollow shaft of outer diameter D0 and inner diameter DI is given by tau max equals 1.066 into 16T upon pi D0 cubed. From the above equations, we can infer that maximum shear stress is directly proportional to the torque applied and inversely proportional to the outer diameter cubed. The power transferred by a shaft is given by the product of 2 pi NT upon 60 into 10 to the power 3, where N is the speed in rpm, theta here is the angle of twist. If two or more shafts of different material, diameter or basic forms are connected together in such a way that each carries the same torque, then shafts are said to be connected in series and the composite shaft so produced is therefore termed as series connected. Here the equilibrium of the shaft requires that a torque T to be same throughout both parts and is given by GJ theta upon L for each shaft. If two or more shafts are regionally fixed together such that the applied torque is shared between them, then the composite shaft so formed is said to be connected in parallel. For parallel connection, torque T equals T1 plus T2 and the angle of twist for each portion are equal and can be obtained from T1 L1 upon G1 J1 equals T2 L2 upon G2 J2, where G and J are shear modulus and polar moment of inertia respectively. Hence, we first saw what torsion is, then saw how stresses occur in hollow and solid shafts and finally saw how shafts are connected in series and parallel. Like, subscribe and comment with your feedback to help us make better videos. Thanks for watching. Also, thanks a lot for those constructive comments. You help the channel grow. So, here are the top mechanical EIs of our last videos. In the next episode of Mechanical EI, find out what strain energy is.