Why Do We Spread Or Extend Our Arms While Trying To Stay Balanced?

On many occasions, we tend to come across broken bridges or bad roads across small lakes or even large gutters. 

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To get past this little hindrance or obstruction, we are always left with just one option; turn around and look for another way. But in most cases, some of us go an extra mile to make a second option; we take the risk of climbing and walking on a broken bridge with narrow pathways.  Also, we all must have noticed how it all goes when we do this. By walking on this narrow path, say the width of a rope, a wooden log or even a pipe, we extend our arms to keep ourselves from plummeting into what lies below.   One amazing thing about this little action is that we weren't told to perform it. It naturally just came into our minds without any thought on our part, and in a matter of seconds, it was executed. But why do we do this?   Let's find out.  Moment Of Inertia  When we talk about the moment of Inertia, we mean a quantity expressing a body's tendency to resist angular acceleration, which is the sum of the products of the mass of each particle in the body with the square of its distance from the axis of rotation. The moment of inertia, otherwise known as the angular mass or rotational inertia, of a rigid body, is a tensor that determines the torque needed for a desired angular acceleration about a rotational axis. It depends on the body's mass distribution and the axis chosen, with more significant moments requiring more torque to change the body's rotation.
 

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Photo Credit: Wikipedia

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An illustration of the moment of Inertia is that of a Flywheel. In other words, the moment of Inertia of an object is what helps that object in maintaining its stability around a given axis. 
 How Does Moment Of Inertia Help In Maintaining Balance?   The moment of Inertia helps us in resisting any rotational movement while we walk on the rope or wooden log. By spreading or extending your arms, you decrease the body mass that appears to be concentrated on your feet, which in this case, serves as the pivot. 

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 When individuals spread their arms, their Inertia, which is the opposition to rotational movement along a given axis, is increased, thereby keeping you and your stability in one piece. And now, we understand why Tightrope walkers usually carry a long pole in the hands.  Stay tuned.