In this video we will explore torsion, which is the twisting of an object caused by a moment. It is a type of deformation. A moment which tends to cause twisting is called torque. Some of the things covered in this video include how circular bars deform under torsion, how we can calculate the angle of twist, and how we can calculate the stresses and strains that are generated in a circular bar as a result of torsion. We will also discuss internal torque diagrams, and why torsional failure is different for brittle and for ductile and materials.