Torsion is when something twists because of a force trying to turn it. This usually happens in round parts, like poles or shafts, used in engineering.

Key Ideas in Torsion:

1. Basic Torsion Equation:
   There's a simple formula that connects torque (the force causing the twist, called $T$), the shape of the object (this is called the polar moment of inertia, or $J$), how the material reacts to stress (called the shear modulus, or $G$), and how much it twists (called the angle of twist, or $\theta$). The equation looks like this:
   $T = J \frac{d\theta}{dz}$
   Here, $z$ means the length of the shaft.

2. Shear Stress in a Shaft:
   Shear stress ($\tau$) happens inside a round shaft when torque is applied. We calculate it using this formula:
   $\tau = \frac{T r}{J}$
   In this, $r$ is the distance from the middle of the shaft to where we’re measuring.

3. Angle of Twist Over Distance:
   To find out how much the shaft twists over a certain length $L$, we can use this formula:
   $\theta = \frac{T L}{J G}$

Where Torsion is Used:

Understanding torsion is super important when designing different parts like drive shafts (which help engines work), beams, and any parts that need to handle twisting forces. It ensures these parts can handle specific twisting forces without breaking.

Recent research shows that when these parts are designed well, they can work safely even when the twisting force is more than 50% of what they can usually handle before failing.