 Welcome back mechanically, did you know that flinched beams were stronger and a flight weight than the beams of their individual materials? This makes us wonder, what are flinched beams? Before we jump in, check out the previous part of this series to learn about what section modulus and moment of resistance are. Now a flinched beam is a compound beam used in the construction of houses, decks and other primary wood frame structures. Typically, the flinched beam is made up of a vertical steel plate sandwiched between two wood beams, the three layers being held together with bolts. Further, alternating layers of wood and steel can be used to produce an even stronger beam. The metal plates within the beam are known as flinch plates because flinched beams are slightly stronger than wood alone, they require less depth than a wood-only beam of the same strength and are much lighter than a steel-only beam of the same size and can still be nailed to the rest of a wooden structure. Moment of inertia is a tensor quantity, that is, it is rotational and log of mass of an object. Just like mass resists acceleration, moment of inertia is something that resists angular acceleration. As moment of inertia is a tensor quantity, it is expressed in the form of a 3x3 matrix. There is always a coordinate system around which the matrix of the tensor diagonalizes itself. If you have its non-zero components only along the diagonal of the matrix, then that moment of inertia measured is called the principal moment of inertia. The axes of such a coordinate system are called principal axes. Hence, we first saw what flinched beams are and then finally saw what principal moment of inertia is. 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 direct and bending stresses are.